The Puerperium & Lactation
Early Embryogenesis &
Maternal Recognition of Pregnancy
Ovulation & Fertilization
Cyclicity
Regulation of
Reproduction
Tract Function
Puberty
Prenatal
Development
Spermatogenesis
Regulat ion of
Reproduction
Tract Function
Puberty
Prenatal
Development
Take Home Message
Gestation is the period of time that a female is pregnant. During gestation, the
placenta forms a major organ of pregnancy that provides an inteJface for metabolic
exchange between the dam and the f etus. Placentas are described mmplwlogically
according to the distribution of villi on the chorionic smface ami the degree of separa..:.
tion between matemal and fetal blood. The placenta is also an endocrine organ that
secretes hormones responsible for: 1) maintenance of pregnancy; 2) stimulation of the
matemal mammmy gland and 3) ensures fetal growth. Parturition is brought about
by secretion of fetal corticoitls and requires removal of the progesterone block. Par-
turition consists of three stages. They are: 1) initiation of myometrial contractions;
2) expulsion ofthe f etus and 3) e.:\:pulsion oftlzefetalmembranes.
The word gestation literally means "the act
of carry ing or being carried". Thus, gestation means
the action or process of carrying or being carried' in
the uterus between conception and birth . · Gest ation
and pregnancy are synonymous and thus, gestation
length means the length of pregnancy. Attachment
of the conceph1s to form an intimate, but temporary,
relationship with the uterus is an evolutionary step that
provides significant advantage to the conceph1s . The
phenomenon of intrauterine development ensures that
the developing conceptus will receive adequate nutri-
tion and protection during its development. In contrast,
lower fon11S of animals lay eggs (oviparous). The
survival of potential offspring of oviparous animals
is jeopardized because the female cannot completely
protect the eggs from environmental and predatmy dan-
ger. Thus, from an evolutionary perspective, eutherian
mammals (mammals with a placenta), are "equipped"
with an in-utero protection mechanism that is highly
successful after the placenta is formed.
The final prepartum steps of
reproduction are:
• formation of a placenta
• acquisition of endocrine function of
the placenta
• initiation of parturition
The term implantation is often used to mean
attachment of the placental membranes to the endo-
metrium in most animals. Achmlly, true implantation
is a phenomenon in humans in which the conceptus
"buries" itself into the uterine endometrium. The con-
ceptus temporarily disappears beneath the surface. In
most other species, the conceph1s does not truly implant,
but rather attaches to the endometrial surface and never
disappears from the luminal compartment.
The placenta is an organ of metabolic inter-
change between the conceph1s and the dam. It is also
an endocrine organ. The placenta is co.
The document summarizes the structure and physiology of the mammalian placenta. It discusses that in viviparous animals, the embryo develops inside the mother's uterus due to insufficient yolk. The embryo attaches to the uterine wall via the placenta to obtain nutrients from the mother's circulation. The placenta allows the exchange of food, oxygen, and waste between the fetus and mother. It then describes different placental structures and classifications in mammals.
USMLE GENERAL EMBRYOLOGY 015 Fetal Membranes-B Fetal Membranes.pdfAHMED ASHOUR
The fetal membranes, also known as the embryonic or fetal membranes, play a crucial role in the development and protection of the embryo/fetus during pregnancy.
Understanding the structure and functions of the fetal membranes is essential for healthcare providers to monitor the health and well-being of both the mother and the developing fetus during pregnancy.
Issues related to the fetal membranes, such as preterm premature rupture of membranes (PPROM), require careful management to
placentation in animals ppt_014943.pptxaatifreyaz5
The document discusses different types of placentation in animals. It begins by describing the basic functions of the placenta in connecting the developing fetus to the uterine wall and facilitating nutrient/gas exchange. There are three main types discussed: 1) choriovitelline placenta, which is a temporary early structure in most mammals formed from yolk sac tissues; 2) chorioallantoic placenta, the definitive placenta of higher mammals formed by attachment of the allantois to the chorion; 3) placentas are further classified as deciduous, non-deciduous, or contra-deciduous based on whether maternal tissues are shed or not during birth. Specific animal examples are
The placenta is a temporary organ that facilitates nutrient and waste exchange between the fetus and mother. It is composed of fetal and maternal tissues. Parturition begins with the fetus triggering hormonal changes that relax the cervix and stimulate contractions. It occurs in three stages: 1) initiation of contractions through decreasing progesterone and increasing prostaglandins and estrogen, 2) expulsion of the fetus aided by hormones like cortisol and relaxin, 3) expulsion of fetal membranes due to villus detachment from maternal tissues. Placentas are classified by villus distribution and layers separating fetal and maternal blood.
Fertilization, implantaion and embryologyobgymgmcri
1. The document summarizes key stages in human development from fertilization through embryonic and fetal development. It describes fertilization, cleavage, implantation, and the formation of the three germ layers and extraembryonic membranes.
2. Implantation of the blastocyst in the endometrium occurs around 7 days after fertilization. The trophoblast erodes into the endometrium and connections are made between embryonic and maternal blood vessels in the placenta.
3. The embryonic phase lasts until 8 weeks when major organ systems have begun to form and it is then called a fetus. By the end of the third month the placenta is functioning to exchange gases, nutrients, and waste
The document discusses the placenta and its functions. It begins by defining the placenta and its origins from Latin. It then discusses:
1) Companies in Japan that produce extracts from human placenta to treat conditions like menopause and hepatitis.
2) The placenta's roles in transporting nutrients, gases, and waste between the mother and fetus. It has endocrine functions and produces hormones to maintain pregnancy and support fetal development.
3) The development of the placenta from the blastocyst stage through implantation and formation of the chorion and villi to facilitate exchanges between mother and fetus.
1. The document discusses the structure and classification of placentas. It describes the different types of placentas found across mammals based on their gross shape, layers between maternal and fetal blood, and histological structure.
2. The major placenta types discussed are epithelio-chorial (found in marsupials and some ungulates), syndesmo-chorial (ruminant ungulates), endothelio-chorial (carnivores), haemochorial (primates and bats), and haemo-endothelial (rodents). Each type involves a different number of layers separating maternal and fetal blood and tissues.
3. Placentas are also classified
The document summarizes the structure and physiology of the mammalian placenta. It discusses that in viviparous animals, the embryo develops inside the mother's uterus due to insufficient yolk. The embryo attaches to the uterine wall via the placenta to obtain nutrients from the mother's circulation. The placenta allows the exchange of food, oxygen, and waste between the fetus and mother. It then describes different placental structures and classifications in mammals.
USMLE GENERAL EMBRYOLOGY 015 Fetal Membranes-B Fetal Membranes.pdfAHMED ASHOUR
The fetal membranes, also known as the embryonic or fetal membranes, play a crucial role in the development and protection of the embryo/fetus during pregnancy.
Understanding the structure and functions of the fetal membranes is essential for healthcare providers to monitor the health and well-being of both the mother and the developing fetus during pregnancy.
Issues related to the fetal membranes, such as preterm premature rupture of membranes (PPROM), require careful management to
placentation in animals ppt_014943.pptxaatifreyaz5
The document discusses different types of placentation in animals. It begins by describing the basic functions of the placenta in connecting the developing fetus to the uterine wall and facilitating nutrient/gas exchange. There are three main types discussed: 1) choriovitelline placenta, which is a temporary early structure in most mammals formed from yolk sac tissues; 2) chorioallantoic placenta, the definitive placenta of higher mammals formed by attachment of the allantois to the chorion; 3) placentas are further classified as deciduous, non-deciduous, or contra-deciduous based on whether maternal tissues are shed or not during birth. Specific animal examples are
The placenta is a temporary organ that facilitates nutrient and waste exchange between the fetus and mother. It is composed of fetal and maternal tissues. Parturition begins with the fetus triggering hormonal changes that relax the cervix and stimulate contractions. It occurs in three stages: 1) initiation of contractions through decreasing progesterone and increasing prostaglandins and estrogen, 2) expulsion of the fetus aided by hormones like cortisol and relaxin, 3) expulsion of fetal membranes due to villus detachment from maternal tissues. Placentas are classified by villus distribution and layers separating fetal and maternal blood.
Fertilization, implantaion and embryologyobgymgmcri
1. The document summarizes key stages in human development from fertilization through embryonic and fetal development. It describes fertilization, cleavage, implantation, and the formation of the three germ layers and extraembryonic membranes.
2. Implantation of the blastocyst in the endometrium occurs around 7 days after fertilization. The trophoblast erodes into the endometrium and connections are made between embryonic and maternal blood vessels in the placenta.
3. The embryonic phase lasts until 8 weeks when major organ systems have begun to form and it is then called a fetus. By the end of the third month the placenta is functioning to exchange gases, nutrients, and waste
The document discusses the placenta and its functions. It begins by defining the placenta and its origins from Latin. It then discusses:
1) Companies in Japan that produce extracts from human placenta to treat conditions like menopause and hepatitis.
2) The placenta's roles in transporting nutrients, gases, and waste between the mother and fetus. It has endocrine functions and produces hormones to maintain pregnancy and support fetal development.
3) The development of the placenta from the blastocyst stage through implantation and formation of the chorion and villi to facilitate exchanges between mother and fetus.
1. The document discusses the structure and classification of placentas. It describes the different types of placentas found across mammals based on their gross shape, layers between maternal and fetal blood, and histological structure.
2. The major placenta types discussed are epithelio-chorial (found in marsupials and some ungulates), syndesmo-chorial (ruminant ungulates), endothelio-chorial (carnivores), haemochorial (primates and bats), and haemo-endothelial (rodents). Each type involves a different number of layers separating maternal and fetal blood and tissues.
3. Placentas are also classified
Review Of Concepts And Intrapartal Handout McnALLEICARG DC
This document provides an overview of maternal and child nursing. It begins by describing the female reproductive anatomy including external organs like the labia and internal organs like the uterus and ovaries. It then discusses the female pelvis and variations in pelvic structure. The document also covers the menstrual cycle and hormonal changes. Finally, it summarizes the stages of fetal development from fertilization through implantation and formation of the placenta and fetal membranes.
The document summarizes the processes of conception, fertilization, implantation, fetal development and the development of organ systems in the fetus. It describes how the ovum and sperm are produced, how fertilization occurs when the sperm meets the ovum, and how the zygote then implants in the uterus. It outlines the stages of development from zygote to embryo to fetus. It also provides details on fetal membranes, the amniotic fluid, umbilical cord and placenta. Finally, it discusses the early development of major organ systems like the cardiovascular, nervous, endocrine, digestive and respiratory systems in the fetus.
Placentation in mammal,classification of placenta and function SoniaBajaj10
The placenta is an organ that develops during pregnancy in mammals to connect the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. It is a discoid, circular organ around 15-20 cm in diameter and 2.5 cm thick that weighs approximately 500g at term. The placenta has both fetal and maternal surfaces, with the fetal surface covered by the amnion and bearing the umbilical cord, and the maternal surface being rough and spongy where it attaches to the uterine wall. The placenta serves critical functions like nutrient, gas and waste exchange between mother and fetus, acting as an endocrine organ and barrier between
Embryology is the study of prenatal development from fertilization through the embryonic and fetal periods. During the embryonic period (first 8 weeks), the three germ layers—ectoderm, mesoderm, and endoderm—develop and give rise to all structures. The fetal period encompasses the remaining 30 weeks of development as structures and organs continue growing and maturing. Fertilization occurs when a sperm fuses with an ovum to form a zygote, which undergoes cleavage, morula, and blastocyst stages over the first week. Around day 6, implantation in the uterus occurs and the blastocyst forms an inner cell mass and trophoblast. The trophoblast develops into the pl
Embryology is the study of prenatal development from fertilization through the embryonic and fetal periods. During the embryonic period (first 8 weeks), the three germ layers—ectoderm, mesoderm, and endoderm—develop and give rise to all structures. The fetal period encompasses the remaining 30 weeks of development as structures and organs continue growing and maturing. Fertilization occurs when a sperm fuses with an ovum to form a zygote, which undergoes cleavage, morula, and blastocyst stages over the first week. Around day 6, implantation in the uterus occurs and the blastocyst forms an inner cell mass and trophoblast. The trophoblast develops into the pl
The placenta facilitates nutrient and gas exchange between maternal and fetal blood. It develops from the fetal trophoblast and maternal endometrium. By the second month, the trophoblast develops into the chorionic villi, which come into contact with maternal blood in the intervillous spaces. The placenta allows for gas exchange, nutrient transport, and provides hormonal support to maintain pregnancy. At term, it is discoid in shape, 15-25 cm in diameter, and weighs 500-600 grams.
The placenta arises from trophoblast tissue and serves as the fetal lungs, kidneys, and gastrointestinal tract throughout pregnancy. It grows equally with the fetus. At term, the placenta is 15-20cm in diameter, 2-3cm thick, and covers half the internal uterus. The placenta establishes circulation between mother and fetus by the 12th day of pregnancy through chorionic villi, allowing nutrients to pass selectively between the maternal and fetal blood while preventing direct exchange. It produces hormones and facilitates gas and nutrient exchange until birth.
Fertilization occurs when an ovum and sperm unite in the fallopian tube. The fertilized egg then undergoes cell division as it travels to the uterus, developing from a morula to a blastocyst. The blastocyst implants in the uterine wall and the placenta begins to form, allowing nutrients to pass from mother to fetus. The placenta, umbilical cord, and amniotic fluid all work to support fetal development in the womb.
1. During the first week after fertilization, the embryo journeys through the fallopian tube undergoing cell division. It then implants in the uterine wall, where the trophoblast cells attach and secrete enzymes to embed the embryo.
2. An elaborate placenta then forms, with intimate apposition of fetal and maternal blood vessels allowing gas exchange, nutrient absorption, and waste excretion for the growing fetus, without actual mixing of blood.
3. Hormonal changes sustain the corpus luteum and uterine lining during pregnancy. The trophoblast secretes hCG to replace LH and stimulate progesterone and estrogen production, initially by the corpus luteum and later directly by the placenta.
The placenta is an organ that develops in mammals during pregnancy to connect the developing fetus to the uterine wall. It allows for nutrient uptake, waste elimination, and gas exchange from the mother's blood supply to nourish the fetus. The placenta has both a fetal component from the chorionic sac and a maternal component from the endometrium. It begins developing upon implantation and grows throughout pregnancy, reaching full development by the end of the first trimester. The placenta plays a vital role in sustaining the fetus during intrauterine development.
Physiology of Fertilization, Implantation, Placental & Fetal DevelopmentEneutron
The document discusses various aspects of human fertilization, implantation, placental and fetal development. It describes the processes of oogenesis and spermatogenesis, how sperm travel through the female reproductive tract and fertilize the egg in the fallopian tubes. It then covers the stages of early embryonic development, implantation in the uterine wall, placental development and formation of the fetal membranes. Key topics include fetal circulation patterns and the roles of the amniotic fluid, umbilical cord and placenta in nutrient/waste exchange between mother and fetus.
18. Pregnancy, Development, and LactationSUNY Ulster
The document describes key processes in pregnancy and lactation including fertilization, implantation, placenta formation, fetal development through the trimesters, parturition, mammary gland development, colostrum production, and lactation. It provides details on the structures and functions of the placenta, umbilical cord, mammary glands, as well as the hormonal factors involved in pregnancy, birth, and nursing.
The document summarizes the female reproductive system. It describes the external and internal reproductive organs, including the ovaries, fallopian tubes, uterus, cervix, and vagina. It discusses the functions of these organs, such as producing eggs and hormones, transporting eggs to the uterus, and providing a site for implantation and childbirth. The document also covers topics like menstruation, the menstrual cycle, and hormones that influence oogenesis and reproduction.
1) The document discusses the embryonic development of the female genital tract. It describes how the müllerian ducts fuse to form the uterus, cervix, and upper vagina while the urogenital sinus forms the lower vagina.
2) Common malformations of the female genital tract include müllerian anomalies like bicornuate or septate uteri, as well as vaginal agenesis where the uterus and vagina are absent.
3) Genital ambiguity in newborns can be due to female pseudohermaphroditism from androgen excess, male pseudohermaphroditism from incomplete androgen development, or true hermaphroditism with
1) This document discusses the embryonic development of the female genital tract. It describes how the müllerian ducts and urogenital sinus form the structures of the female reproductive system between 6-12 weeks of gestation.
2) It also discusses common malformations that can occur when development goes awry, such as vaginal agenesis, uterine anomalies, and ambiguous genitalia in newborns.
3) Genital ambiguity in newborns can be caused by excess androgen exposure leading to pseudohermaphroditism, dysgenetic gonads, or in rare cases true hermaphroditism. The document provides examples of each condition.
The male and female reproductive systems ensure sexual maturation and propagation of future generations. Both systems have gonads that produce gametes and sex hormones, becoming functional at puberty. While similarities exist, including homologous organs developing from similar tissues, differences include males continuously producing sperm after puberty versus females' relatively fixed number of ova released periodically. Fertilization typically occurs in the fallopian tubes when sperm meets an ovum.
The placenta develops from the trophoblast layers of the fertilized egg and connects the developing fetus to the uterine wall. It allows for nutrient and gas exchange between the mother and fetus's blood supply. The placenta grows throughout pregnancy and is fully developed by the end of the first trimester. It has both a maternal and fetal surface and connects to the fetus via the umbilical cord. The placenta functions to provide nutrition, gas exchange, waste removal, hormone production, storage, and protection for the fetus. Abnormalities like placenta accreta, increta, percreta, previa and abruptio placentae can complicate delivery and cause hemorrhaging. The placent
This document provides an introductory lecture on infertility and sterility for veterinary students. It discusses the key reproductive organs and hormones involved in the estrous cycle. It describes how the hypothalamus and pituitary gland regulate reproduction and the roles of the ovaries, uterus, cervix and other female organs. It then covers factors that can influence infertility and sterility, including endocrinological disorders, mismanagement, reproductive diseases, anatomical defects, and environmental defects. Finally, it discusses reproductive efficiency and various reproductive indices used to measure performance.
This document discusses placental classification in mammals. It describes how placentas are classified based on the fetal membranes involved (yolk sac or chorioallantoic), nature of contact with the uterus (indeciduate or deciduate), villi distribution (diffuse, cotyledonary, etc.), and histological intimacy with maternal tissues (epitheliochorial, syndesmochorial, etc.). The formation and development of the placenta from implantation through birth is explained. Various placental structures and types found in different mammalian orders are outlined.
Embryology is the study of prenatal development to understand how anatomical structures form. The major events of the first week include conception, formation of the zygote, cleavage into blastomeres, formation of the morula and blastocyst. The blastocyst undergoes implantation in the endometrium between days 6-7. This involves apposition, adhesion, penetration and invasion. The trophoblast differentiates and the inner cell mass forms the embryo proper. During the embryonic period from weeks 4-8, the three germ layers form and all major structures and organs develop. By the end of the embryonic period at 8 weeks, the embryo has distinct human form and features.
Write a scholarly paper in which you apply the concepts of epide.docxarnoldmeredith47041
This document provides requirements for an epidemiology paper that analyzes a communicable disease. Students must choose a communicable disease, describe it thoroughly including causes, transmission, symptoms, treatment and complications. They must discuss the population most affected by the disease and the determinants of health related to it. Students must also identify the epidemiologic triad of host, agent, and environmental factors for the disease and discuss the role of public health nurses in finding, reporting, collecting, analyzing data, and following up on the disease. The paper requires a minimum of three references and 1250 words in APA format.
Write a S.M.A.R.T. goal to improve the Habit 5 Seek First to .docxarnoldmeredith47041
This document outlines a goal to improve the ability to seek first to understand others rather than be understood according to Habit 5. The author acknowledges they are able to communicate but struggles with listening skills. The goal is to practice actively listening and understanding what people are saying rather than being focused on themselves.
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This document provides an overview of maternal and child nursing. It begins by describing the female reproductive anatomy including external organs like the labia and internal organs like the uterus and ovaries. It then discusses the female pelvis and variations in pelvic structure. The document also covers the menstrual cycle and hormonal changes. Finally, it summarizes the stages of fetal development from fertilization through implantation and formation of the placenta and fetal membranes.
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The placenta is an organ that develops during pregnancy in mammals to connect the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. It is a discoid, circular organ around 15-20 cm in diameter and 2.5 cm thick that weighs approximately 500g at term. The placenta has both fetal and maternal surfaces, with the fetal surface covered by the amnion and bearing the umbilical cord, and the maternal surface being rough and spongy where it attaches to the uterine wall. The placenta serves critical functions like nutrient, gas and waste exchange between mother and fetus, acting as an endocrine organ and barrier between
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Embryology is the study of prenatal development from fertilization through the embryonic and fetal periods. During the embryonic period (first 8 weeks), the three germ layers—ectoderm, mesoderm, and endoderm—develop and give rise to all structures. The fetal period encompasses the remaining 30 weeks of development as structures and organs continue growing and maturing. Fertilization occurs when a sperm fuses with an ovum to form a zygote, which undergoes cleavage, morula, and blastocyst stages over the first week. Around day 6, implantation in the uterus occurs and the blastocyst forms an inner cell mass and trophoblast. The trophoblast develops into the pl
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The placenta arises from trophoblast tissue and serves as the fetal lungs, kidneys, and gastrointestinal tract throughout pregnancy. It grows equally with the fetus. At term, the placenta is 15-20cm in diameter, 2-3cm thick, and covers half the internal uterus. The placenta establishes circulation between mother and fetus by the 12th day of pregnancy through chorionic villi, allowing nutrients to pass selectively between the maternal and fetal blood while preventing direct exchange. It produces hormones and facilitates gas and nutrient exchange until birth.
Fertilization occurs when an ovum and sperm unite in the fallopian tube. The fertilized egg then undergoes cell division as it travels to the uterus, developing from a morula to a blastocyst. The blastocyst implants in the uterine wall and the placenta begins to form, allowing nutrients to pass from mother to fetus. The placenta, umbilical cord, and amniotic fluid all work to support fetal development in the womb.
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2. An elaborate placenta then forms, with intimate apposition of fetal and maternal blood vessels allowing gas exchange, nutrient absorption, and waste excretion for the growing fetus, without actual mixing of blood.
3. Hormonal changes sustain the corpus luteum and uterine lining during pregnancy. The trophoblast secretes hCG to replace LH and stimulate progesterone and estrogen production, initially by the corpus luteum and later directly by the placenta.
The placenta is an organ that develops in mammals during pregnancy to connect the developing fetus to the uterine wall. It allows for nutrient uptake, waste elimination, and gas exchange from the mother's blood supply to nourish the fetus. The placenta has both a fetal component from the chorionic sac and a maternal component from the endometrium. It begins developing upon implantation and grows throughout pregnancy, reaching full development by the end of the first trimester. The placenta plays a vital role in sustaining the fetus during intrauterine development.
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1) The document discusses the embryonic development of the female genital tract. It describes how the müllerian ducts fuse to form the uterus, cervix, and upper vagina while the urogenital sinus forms the lower vagina.
2) Common malformations of the female genital tract include müllerian anomalies like bicornuate or septate uteri, as well as vaginal agenesis where the uterus and vagina are absent.
3) Genital ambiguity in newborns can be due to female pseudohermaphroditism from androgen excess, male pseudohermaphroditism from incomplete androgen development, or true hermaphroditism with
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2) It also discusses common malformations that can occur when development goes awry, such as vaginal agenesis, uterine anomalies, and ambiguous genitalia in newborns.
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The placenta develops from the trophoblast layers of the fertilized egg and connects the developing fetus to the uterine wall. It allows for nutrient and gas exchange between the mother and fetus's blood supply. The placenta grows throughout pregnancy and is fully developed by the end of the first trimester. It has both a maternal and fetal surface and connects to the fetus via the umbilical cord. The placenta functions to provide nutrition, gas exchange, waste removal, hormone production, storage, and protection for the fetus. Abnormalities like placenta accreta, increta, percreta, previa and abruptio placentae can complicate delivery and cause hemorrhaging. The placent
This document provides an introductory lecture on infertility and sterility for veterinary students. It discusses the key reproductive organs and hormones involved in the estrous cycle. It describes how the hypothalamus and pituitary gland regulate reproduction and the roles of the ovaries, uterus, cervix and other female organs. It then covers factors that can influence infertility and sterility, including endocrinological disorders, mismanagement, reproductive diseases, anatomical defects, and environmental defects. Finally, it discusses reproductive efficiency and various reproductive indices used to measure performance.
This document discusses placental classification in mammals. It describes how placentas are classified based on the fetal membranes involved (yolk sac or chorioallantoic), nature of contact with the uterus (indeciduate or deciduate), villi distribution (diffuse, cotyledonary, etc.), and histological intimacy with maternal tissues (epitheliochorial, syndesmochorial, etc.). The formation and development of the placenta from implantation through birth is explained. Various placental structures and types found in different mammalian orders are outlined.
Embryology is the study of prenatal development to understand how anatomical structures form. The major events of the first week include conception, formation of the zygote, cleavage into blastomeres, formation of the morula and blastocyst. The blastocyst undergoes implantation in the endometrium between days 6-7. This involves apposition, adhesion, penetration and invasion. The trophoblast differentiates and the inner cell mass forms the embryo proper. During the embryonic period from weeks 4-8, the three germ layers form and all major structures and organs develop. By the end of the embryonic period at 8 weeks, the embryo has distinct human form and features.
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CONTACT INFO
First and Last Name
City, State (Optional) | Best Phone Number to Reach You | Appropriate Email Address
SUMMARY OF QUALIFICATIONS
· 3-5 sentences describing why you would be a great fit for the position.
· Describe your relevant accomplishments, strengths, knowledge, experience, skillsets, and languages.
· This is the “preview to the movie.” Highlight your best qualifications so they choose to read the rest of the resume.
· Use bullet points to distinguish each sentence if more aesthetically pleasing.
PROFESSIONAL EXPERIENCE
· List jobs you have held in the past 10 years; only list older jobs if they are directly related to desired job.
· Do NOT list a job if you worked at a place of employment for less than 3 months.
· If you have some jobs that are related to your desired position/field and others that are not, only list the related jobs in this section. Create an “Additional Work History” section at the end of the resume for the non-related jobs.
· Use bullet points to list achievements, results, recognitions, and duties for each job.
Company Name - City, State
Job Title
Start Year - End Year or Present
3-5 achievements, results, recognitions, and duties
INTERNSHIP / EXTERNSHIP / CLINICAL EXPERIENCE
· This section should take priority over others unless you have previous work history in exact field.
Company Name - City, State
Title or Role
Month Year - Month Year
2-3 Main Responsibilities/Duties
CERTIFICATIONS and LICENSURES
Name of Certification/License
Issuing Company or Organization
Certification/License Number
Expiration Month Year
EDUCATION
· Only include schools that you received a degree or relevant certifications from, or are currently attending.
· Do NOT include your high school.
School Name - City, State
Major/Area of Study
Degree Earned
Graduation Year/Estimated Graduation Month Year
CORE COMPETENCIES
· List 6-9 competencies, skills, traits, and/or areas of proficiency that directly relate to the job.
· Utilize the job description to find the types of preferred and/or required skills and traits.
· This is a great area to match keywords from the job description that may not otherwise be easily listed in your resume.
· Use bullet points and columns to make this section more aesthetically pleasing and organized.
RELEVANT COURSEWORK
· List the core courses you have already completed and are currently in.
· Use bullet points to list each course.
VOLUNTEER WORK / AFFILIATIONS
Organization
City, State
example of resume
SHARKLY BRUCE, COTA/L
Amity Island, FL | (975) 206-1120 |
[email protected]
SUMMARY OF QUALIFICATIONS
· Certified Occupational Therapy Assistant with two 8-week rotations of Level II OTA fieldwork, as well as 3 years of previous healthcare experience in a hospital setting.
· Extensive direct care experience assisting patients after treatment of traumatic wounds from local wildlife attacks.
· Proven track record o.
Write a resume and cover letter for the following positionOnline.docxarnoldmeredith47041
Write a resume and cover letter for the following position
Online Marketing Strategist
Riverside, CA 92507
Full-time, Contract
Raincross is seeking a full time marketing rockstar to manage client accounts, devise and implement strategies and craft winning content daily. Candidates must be extremely motivated, possess excellent research and writing skills and pay very close attention to detail.
Requirements
Master the art of creating content: blog articles, updates on social sites, press releases, infographics (or at least the concepts behind them for our design team to create) are all part of the ideal candidates daily tasks
Research and analyze the latest data to uncover gaps; stay up to date on the latest trends and be quick enough to jump on them before they pass
Convert through compelling CTA’s: Create copy for signage, newsletters, email campaigns, online promotions, ads, etc to help brand reach their goals
A/B test: Do you know what works and what doesn’t?
Craft brand strategies: Figure out what they’re doing right, what they’re doing wrong and create strategies to implement. Research to include competitor marketing, trends, etc. Come up with creative new ways to help clients grow and become more successful
Social advertising: Run ads on Facebook, Instagram, Twitter, LinkedIn and any other social platform that allows us to
Responsibilities
Bachelors Degree in Communications, Marketing or similar
Excellent written and verbal communication and customer service skills
Must take initiative, possess creativity, be hands on and a team player
Should be open-minded, a fast learner, enthusiastic, and adaptable
Experience in writing, copy-writing, researching trends, analyzing data, a/b testing, brand strategies and running social ads and campaigns a huge plus
.
Write a response to the peers post based on the readings. Origi.docxarnoldmeredith47041
Write a response to the peer's post based on the readings.
Original Prompt:
Compare Carroll's strategies for creating sound in
Jabberwocky
with those used by Swenson in
A Nosty
Fright.
Pay attention to connotative and denotative meanings of the words and how the poet plays with sound.
Edilzon Ramirez
Response to Prompt:
In both poems there is a common element. And that is a wordplay to make nonsense poetry. The effect of this, is that we must think more in depth to figure out the real meaning behind the works of literature. In Jabberwocky, the writer begins by setting up the mood giving us the background of the events that are about to occur. The use of exclamation marks throughout the poem afterwards, are what in my opinion, give it the sound. For example, “O frabjous day! Callooh! Callay!” suggests sort of a proud/relived cry. Which is furthered backed up by the whimsical words that have a positive connation to them due to the slaying of the jabberwocky, who terrorized the people.
While in “A Nosty Fright” another poem with nonsense words or portmanteau the mood is sad, and it only becomes gloomier. Like Miss Brill, the poet describes things together, in the first stanza “roldengod and the soneyhuckle” and jumps to a lonely chipmunk, suggesting that it has lost its companion. There is hope for it when it meets the grasshopper. Ultimately, it comes to an end “Here we part,” said the hassgropper. “Pere we hart,” mipchunk, too”. All hope is lost for the chipmunk and is waiting for the winter to come. This symbolizes death because during the months of October, November, and December many mammals including the chipmunks hibernate and its almost like it wanted to go to sleep permanently remarking things like “Will it ever be morning, Nofember virst”.
Some say, that the chipmunk is a representation of the author and her sexuality. She like the chipmunk, was alone and the typhoon that was mentioned earlier, was her losing her mind. The words and the sounds they make, further makes this evident because it is gibberish written by someone who is broken.
(Your response to your peer should add or extend the point given by your peer.)
.
Write a response to the following prompt.Analyze the characteriz.docxarnoldmeredith47041
Write a response to the following prompt.
Analyze the characterization Shakespeare employed in
Julius Caesar
, paying particular attention to the role of women. (50 pts) Remember, as you write, to use the language of characterization as we have discussed in class.
.
Write a response to a peers post that adds or extends to the discus.docxarnoldmeredith47041
Write a response to a peer's post that adds or extends to the discussion point of your peer by Friday 07/24/2020.
This week's discussion prompt:
Explain how Faith in "Young Goodman Brown," Georgiana in "The Birthmark," and Elizabeth in "The Black Minister's Veil" are use to reveal some truth about the central male characters in each story. Describe the similarities that you see among these women characters.
Peer's Post:
-Emily Seide
In each of the three short stories, the female characters play a large role in the character development of the three male protagonists (Goodman, Aylmer, and Hooper). Throughout each story, the women leave a lasting impact on their significant other’s mentality of the world and perception of others. In “Young Goodman Brown”, Brown is faced with troubling sights that make him alter his point of view on his town and the townspeople. Brown was introduced to the true form of some nasty people, including his wife, Faith. When he returns home the next morning from a place of sinister evil, his encounter with Faith and his townspeople has made him a hardcore skeptic of anyone and everyone around him. Goodman Brown never trusted a soul after that night because he was forced to believe that evil resides in everyone. In “The Birthmark”, Aylmer goes insane trying to remove his wife, Georgiana’s, birthmark. Even after hearing how beautiful and well liked she is, Georgiana agrees to get her birthmark removed. Rather than seeing this as a perfect part of her, Aylmer sees the birthmark as a flaw that gives her an imperfect complexion. Later in the story, as the birthmark fades and she wakes up, she states that he should’ve admired what he had in the first place, then dies. This made Aylmer realize that he took time for granted, and now he lives a life without Georgiana due to his impatience with her already beautiful complexion. And finally, in “The Minister’s Black Veil”, Reverend Hooper consistently wears a black veil that covers the majority of his face. Several people were afraid and intimidated by it, except for his fiancée, Elizabeth. After further questioning, she begins to fear the veil due to what it symbolizes- the sin in all human beings. Hooper’s plea for Elizabeth to stay reveals the extent of which he is willing to sacrifice, and the decision for him to continue to wear the veil reveals great sorrow; “Do not leave me in this miserable obscurity forever!” (Hawthorne, 36). In each of the short stories, each female character, always a love interest, is first skeptical of the main character’s choice of actions, then later comply. In each short story, a life lesson is learned for each male character.
Readings are attached!
.
Write a response mini-essay of at least 150 to 300 words on the dis.docxarnoldmeredith47041
Write a response mini-essay of at least 150 to 300 words on the discussion topic identified below. Take a position and defend it. (Specify a thesis and support it very briefly with evidence)
The response essay should provide one example from the contemporary world to support your
Position. Ideally you have a source reference for your example. You must have a source reference if you
Refer to any material which is neither common knowledge nor personal experience. essay should be typed using
APA style
feature with a title page and list of references if any are used.
Topic:
Technology changes education
Postman argues that television technology substantively changes aspects of culture such as news, politics, religion, and education in ways that suit the technology, not the human culture that uses the technology. It is a point others have made as well, though it is still contested by many other philosophers and social critics. One excellent example of technological change is on-line course delivery. While there are some who say that the new medium does not provide an education, others (such as your instructor) believe they can accomplish a better education in some subject areas. What have you noticed? What differences are there in on-line education that are due to the way it is technologically mediated? What differences do they make in the education you are receiving? Do you think this is a better or worse education? Why might your instructor think it can be better (and not just because he manages the class while in his pajamas)?
.
Write a response for each document.Instructions Your post sho.docxarnoldmeredith47041
Write a response for each document.
Instructions:
Your post should be a thoughtful response and should include outside reference material from the internet or primary literature. That reference should be referred to specifically with an in-text citation (author, year) and your post should have a bibliography with those outside sources you used cited in APA format.
.
write a resonse paper mla styleHAIRHair deeply affects people,.docxarnoldmeredith47041
write a resonse paper mla style
HAIR
Hair deeply affects people, can transfigure or repulse them. Symbolic of life, hair bolts from our head. Like the earth, it can be harvested, but it will rise again. We can change its color and texture when the mood strikes us, but in time it will return to its original form, just as Nature will in time turn our precisely laid-out cities into a weed-way. Giving one's lover a lock of hair to wear in a small locket [3] around his neck used to be a moving and tender gesture, but also a dangerous one, since to spell-casters, magicians, voodoo-ers, and necromancers of all sorts, a tuft of someone's hair could be used to cast a spell against them. In a variation on this theme, a medieval knight wore a lock of his lady's pubic hair into battle. Since one of the arch-tenets of courtly love was secrecy, choosing this tiny memento instead of a lock of hair from her head may have been more of a practical choice than a philosophical one, but it still symbolized her life-force, which he was carrying with him. Ancient male leaders wore long flowing tresses as a sign of virility (in fact,
"kaiser" and "tsar" both mean "long-haired"
). In the biblical story of Samson, the hero's loss of hair brings on his weakness and downfall, just as it did for the hero Gilgamesh before him. In Europe in more recent times, women who collaborated with the enemy in World War II were humiliated by having their hair cut short. Among some orthodox Jews, a young woman must cut off her hair when she marries, lest her husband find her too attractive and wish to have sex with her out of desire rather than for procreation. Rastafarians regard their dreadlocks as "high-tension cables to heaven." These days, to shock the bourgeoisie and establish their own identity, as every generation must, many young men and women wear their hair as freeform sculpture, with lacquered spikes, close-cropped patterns that resemble a formal garden maze, and colors borrowed from an aviary or spray-painted alley. The first time a student walked into my classroom wearing a "blue jay," it did startle me. Royal-blue slabs of hair were brushed and sprayed straight up along the sides of his head, a long jelly roll of white hair fell forward over his eyebrows, and the back was shiny black, brushed straight up and plastered close to the head. I didn't dislike it, it just seemed like a lot to fuss with each day. I'm sure my grandmother felt that way about my mother's "beehive," and I know my mother feels that way about the curly weather system which is my own mane of long thick hair. One's hairstyle can be the badge of a group, as we've always known -- look at the military's crew cut, or the hairstyles worn by some nuns and monks. In the sixties, wearing long hair, especially if you were a man, often fetched a vitriolic outburst from parents, which is why the musical Hair summed up a generation so beautifully. The police, who seemed so clean-cut and cropped then, were succee.
Write a response about the topic in the reading (see attached) and m.docxarnoldmeredith47041
Write a response about the topic in the reading (see attached) and make sure you include the following:
1. Brief summary of the reading
2. What was intersting?
3. The main points highlighted and what do you think of the reading?
( 2 page response)
.
Write a research report based on a hypothetical research study. Con.docxarnoldmeredith47041
Write a research report based on a hypothetical research study. Conducting research and writing a report is common practice for many students and practitioners in any of the behavioral sciences fields.
A research report, which is based on scientific method, is typically composed of the different sections listed below:
Introduction:
The introduction states a specific hypothesis and how that hypothesis was derived by connecting it to previous research.
Methods:
The methods section describes the details of how the hypothesis was tested and clarifies why the study was conducted in that particular way.
Results:
The results section is where the raw uninterpreted data is presented.
Discussion:
The discussion section is where an argument is presented on whether or not the data supports the hypothesis, the possible implications and limitations of the study, as well as possible future directions for this type of research.
Together, these sections should tell the reader what was done, how it was done, and what was learned through the research. You will create a research report based on a
hypothetical
problem, sample, results, and literature review. Organize your data by creating meaningful sections within your report. Make sure that you:
Apply key concepts of inferential hypothesis tests.
Interpret the research findings of the study.
Examine the assumptions and limitations of inferential tests.
Develop a practical application of the research principles covered in this course.
Focus of the Research Report
To begin, create a hypothetical research study (you do not have to carry out the study; you will just have to describe it) that is based on the three pieces of information listed below. Once you have your hypothetical study created, write a three- to four-page research report (excluding title and reference pages) that outlines the study. You are encouraged to be creative with your research study, but be sure to follow the format outlined below and adhere to APA formatting as outlined in the Ashford Writing Center.
Your hypothetical research study should be based on the following information:
Recent research has indicated that eating chocolate can improve memory. Jones and Wilson (2011) found that eating chocolate two hours before taking math tests improved scores significantly. Wong, Hideki, Anderson, and Skaarsgard (2009) found that women are better than men on memory tests after eating chocolate.
There were 50 men and 50 women who were randomly selected from a larger population.
A
t
-test was conducted to compare men and women’s performance on an assessment after eating chocolate. The results showed an independent
t
-test value of
t
.05(99) = 3.43;
p
< .05
Your research study must contain the following:
Title Page
Title of your report
Your name
The course
Instructor
Date
Introduction
Introduce the research topic, explain why it is important, and present the purpose of the paper and the resea.
Write a Research Paper with the topic Pregnancy in the adolesce.docxarnoldmeredith47041
Write a Research Paper with the topic: Pregnancy in the adolescent life.
The conditions are:
APA format
Double space
One inch margin on all sides
All paragraph in the body are indented
The title is centered on the page with your name and school institution
Paragraph 2, 3, and 4 need another inch more
All pages should be numbered and with citation
Apart of the Research paper write the topic sentence (a question or a statement) & the THESIS of the Research Paper. Write 3 citations for your Research Paper.
.
Write a Research Paper with the topic Autism a major problem. T.docxarnoldmeredith47041
Write a Research Paper with the topic: Autism a major problem.
The conditions are:
APA format
Double space
One inch margin on all sides
All paragraph in the body are indented
The title is centered on the page with your name and school institution
Paragraph 2, 3, and 4 need another inch more
All pages should be numbered and with citation
Apart of the Research paper write the topic sentence (a question or a statement) & the THESIS of the Research Paper.
Write 3 citations for your Research Paper.
.
Write a research paper that explains how Information Technology (IT).docxarnoldmeredith47041
Write a research paper that explains how Information Technology (IT) promotes getting people who are affected by policies involved in the policy-making process. Cite specific examples.
1000- 1200 words APA format and
Create a powerpoint presentation using 5 slides on the main points covered in your research paper. You may use a title slide and a reference slide.
Please find the attached text book.
.
Write a research paper outlining possible career paths in the field .docxarnoldmeredith47041
Write a research paper outlining possible career paths in the field of Human Resources Management (HRM) and based upon independent research discuss how different organizations might develop and implement a strategic HRM plan.
Research Paper Instructions:
IMPORTANT!!
Submit your work as an MS WORD ATTACHMENT in either a .doc, .docx, or .rtf format.
Please support your ideas, arguments, and opinions with independent research, include at least three (3) supporting references or sources (NOT Wikipedia, unknown, or anonymous sources), format your work in proper APA format, include a cover page, an abstract, an introduction and a labeled conclusion in accordance with the course rubric, a minimum of 3 FULL pages of written content, and a reference section. Double space all work and cite all listed references properly in text in accordance with the 6th edition of the APA manual, chapters 6 & 7.
.
Write a Research paper on the Legal issues associated with pentestin.docxarnoldmeredith47041
Write a Research paper on the Legal issues associated with pentesting.
Paper Specifics
3000 words (not counting citations)
APA format
Max team size of two
Minimum 5 academic sources
Provides clear summary and introduction to project scope; includes coherent discussion of key concepts, principles, and problem statement; develops clear context between project tasks and performing security testing in a virtual environment
Provides a thorough and concise summary of the project by listing the purpose and results of each test conducted; or research summary; clearly links the results with recommendations/research, which are supported by test data and external references
.
Write a research paper on one of the following topics .docxarnoldmeredith47041
Write a research paper on
one
of the following topics:
1. What are the effects of corruption on capitalism and foreign investment? (Unit II)
Be sure to include at least the following points in your paper:
What are the types of corruption?
What are effects of corruption on MNCs?
How can MNCs deal effectively with these problems?
2. How can MNCs effectively negotiate with local employees, local suppliers, and local governments in the Middle East? (Unit IV)
Be sure to include at least the following points in your paper:
What are some examples of negotiation cases in the Middle East?
How do MNCs use negotiation to solve problems?
What roles do different cultures have in negotiation?
3. Discuss the problems MNCs face when assigning expatriates to an Eastern European country and how they should support the expatriates. (Unit VII)
Be sure to include at least the following points in your paper:
What are problems for international assignments in Eastern Europe?
What are solutions for the problems?
What are strategies MNCs can implement to support their expatriates?
Directions:
The paper should be at least 750 words in length.
You are required to use a minimum of three scholarly sources for the paper.
All sources used must be referenced; paraphrased and quoted material must have accompanying APA citations.
.
Main Java[All of the Base Concepts}.docxadhitya5119
This is part 1 of my Java Learning Journey. This Contains Custom methods, classes, constructors, packages, multithreading , try- catch block, finally block and more.
ISO/IEC 27001, ISO/IEC 42001, and GDPR: Best Practices for Implementation and...PECB
Denis is a dynamic and results-driven Chief Information Officer (CIO) with a distinguished career spanning information systems analysis and technical project management. With a proven track record of spearheading the design and delivery of cutting-edge Information Management solutions, he has consistently elevated business operations, streamlined reporting functions, and maximized process efficiency.
Certified as an ISO/IEC 27001: Information Security Management Systems (ISMS) Lead Implementer, Data Protection Officer, and Cyber Risks Analyst, Denis brings a heightened focus on data security, privacy, and cyber resilience to every endeavor.
His expertise extends across a diverse spectrum of reporting, database, and web development applications, underpinned by an exceptional grasp of data storage and virtualization technologies. His proficiency in application testing, database administration, and data cleansing ensures seamless execution of complex projects.
What sets Denis apart is his comprehensive understanding of Business and Systems Analysis technologies, honed through involvement in all phases of the Software Development Lifecycle (SDLC). From meticulous requirements gathering to precise analysis, innovative design, rigorous development, thorough testing, and successful implementation, he has consistently delivered exceptional results.
Throughout his career, he has taken on multifaceted roles, from leading technical project management teams to owning solutions that drive operational excellence. His conscientious and proactive approach is unwavering, whether he is working independently or collaboratively within a team. His ability to connect with colleagues on a personal level underscores his commitment to fostering a harmonious and productive workplace environment.
Date: May 29, 2024
Tags: Information Security, ISO/IEC 27001, ISO/IEC 42001, Artificial Intelligence, GDPR
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Find out more about ISO training and certification services
Training: ISO/IEC 27001 Information Security Management System - EN | PECB
ISO/IEC 42001 Artificial Intelligence Management System - EN | PECB
General Data Protection Regulation (GDPR) - Training Courses - EN | PECB
Webinars: https://pecb.com/webinars
Article: https://pecb.com/article
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For more information about PECB:
Website: https://pecb.com/
LinkedIn: https://www.linkedin.com/company/pecb/
Facebook: https://www.facebook.com/PECBInternational/
Slideshare: http://www.slideshare.net/PECBCERTIFICATION
Chapter wise All Notes of First year Basic Civil Engineering.pptxDenish Jangid
Chapter wise All Notes of First year Basic Civil Engineering
Syllabus
Chapter-1
Introduction to objective, scope and outcome the subject
Chapter 2
Introduction: Scope and Specialization of Civil Engineering, Role of civil Engineer in Society, Impact of infrastructural development on economy of country.
Chapter 3
Surveying: Object Principles & Types of Surveying; Site Plans, Plans & Maps; Scales & Unit of different Measurements.
Linear Measurements: Instruments used. Linear Measurement by Tape, Ranging out Survey Lines and overcoming Obstructions; Measurements on sloping ground; Tape corrections, conventional symbols. Angular Measurements: Instruments used; Introduction to Compass Surveying, Bearings and Longitude & Latitude of a Line, Introduction to total station.
Levelling: Instrument used Object of levelling, Methods of levelling in brief, and Contour maps.
Chapter 4
Buildings: Selection of site for Buildings, Layout of Building Plan, Types of buildings, Plinth area, carpet area, floor space index, Introduction to building byelaws, concept of sun light & ventilation. Components of Buildings & their functions, Basic concept of R.C.C., Introduction to types of foundation
Chapter 5
Transportation: Introduction to Transportation Engineering; Traffic and Road Safety: Types and Characteristics of Various Modes of Transportation; Various Road Traffic Signs, Causes of Accidents and Road Safety Measures.
Chapter 6
Environmental Engineering: Environmental Pollution, Environmental Acts and Regulations, Functional Concepts of Ecology, Basics of Species, Biodiversity, Ecosystem, Hydrological Cycle; Chemical Cycles: Carbon, Nitrogen & Phosphorus; Energy Flow in Ecosystems.
Water Pollution: Water Quality standards, Introduction to Treatment & Disposal of Waste Water. Reuse and Saving of Water, Rain Water Harvesting. Solid Waste Management: Classification of Solid Waste, Collection, Transportation and Disposal of Solid. Recycling of Solid Waste: Energy Recovery, Sanitary Landfill, On-Site Sanitation. Air & Noise Pollution: Primary and Secondary air pollutants, Harmful effects of Air Pollution, Control of Air Pollution. . Noise Pollution Harmful Effects of noise pollution, control of noise pollution, Global warming & Climate Change, Ozone depletion, Greenhouse effect
Text Books:
1. Palancharmy, Basic Civil Engineering, McGraw Hill publishers.
2. Satheesh Gopi, Basic Civil Engineering, Pearson Publishers.
3. Ketki Rangwala Dalal, Essentials of Civil Engineering, Charotar Publishing House.
4. BCP, Surveying volume 1
Gender and Mental Health - Counselling and Family Therapy Applications and In...PsychoTech Services
A proprietary approach developed by bringing together the best of learning theories from Psychology, design principles from the world of visualization, and pedagogical methods from over a decade of training experience, that enables you to: Learn better, faster!
Beyond Degrees - Empowering the Workforce in the Context of Skills-First.pptxEduSkills OECD
Iván Bornacelly, Policy Analyst at the OECD Centre for Skills, OECD, presents at the webinar 'Tackling job market gaps with a skills-first approach' on 12 June 2024
Strategies for Effective Upskilling is a presentation by Chinwendu Peace in a Your Skill Boost Masterclass organisation by the Excellence Foundation for South Sudan on 08th and 09th June 2024 from 1 PM to 3 PM on each day.
Your Skill Boost Masterclass: Strategies for Effective Upskilling
The Puerperium & Lactation Early Embryogenesis & Materna.docx
1. The Puerperium & Lactation
Early Embryogenesis &
Maternal Recognition of Pregnancy
Ovulation & Fertilization
Cyclicity
Regulation of
Reproduction
Tract Function
Puberty
Prenatal
Development
Spermatogenesis
Regulat ion of
Reproduction
Tract Function
Puberty
Prenatal
Development
Take Home Message
2. Gestation is the period of time that a female is pregnant. During
gestation, the
placenta forms a major organ of pregnancy that provides an
inteJface for metabolic
exchange between the dam and the f etus. Placentas are
described mmplwlogically
according to the distribution of villi on the chorionic smface
ami the degree of separa..:.
tion between matemal and fetal blood. The placenta is also an
endocrine organ that
secretes hormones responsible for: 1) maintenance of
pregnancy; 2) stimulation of the
matemal mammmy gland and 3) ensures fetal growth.
Parturition is brought about
by secretion of fetal corticoitls and requires removal of the
progesterone block. Par-
turition consists of three stages. They are: 1) initiation of
myometrial contractions;
2) expulsion ofthe f etus and 3) e.::pulsion
oftlzefetalmembranes.
The word gestation literally means "the act
of carry ing or being carried". Thus, gestation means
the action or process of carrying or being carried' in
the uterus between conception and birth . · Gest ation
and pregnancy are synonymous and thus, gestation
length means the length of pregnancy. Attachment
of the conceph1s to form an intimate, but temporary,
relationship with the uterus is an evolutionary step that
provides significant advantage to the conceph1s . The
phenomenon of intrauterine development ensures that
the developing conceptus will receive adequate nutri-
tion and protection during its development. In contrast,
lower fon11S of animals lay eggs (oviparous). The
survival of potential offspring of oviparous animals
3. is jeopardized because the female cannot completely
protect the eggs from environmental and predatmy dan-
ger. Thus, from an evolutionary perspective, eutherian
mammals (mammals with a placenta), are "equipped"
with an in-utero protection mechanism that is highly
successful after the placenta is formed.
The final prepartum steps of
reproduction are:
• formation of a placenta
• acquisition of endocrine function of
the placenta
• initiation of parturition
The term implantation is often used to mean
attachment of the placental membranes to the endo-
metrium in most animals. Achmlly, true implantation
is a phenomenon in humans in which the conceptus
"buries" itself into the uterine endometrium. The con-
ceptus temporarily disappears beneath the surface. In
most other species, the conceph1s does not truly implant,
but rather attaches to the endometrial surface and never
disappears from the luminal compartment.
The placenta is an organ of metabolic inter-
change between the conceph1s and the dam. It is also
an endocrine organ. The placenta is composed of a fetal
component derived fi·om the chorion and a maternal
component derived from modifications of the uterine
endometrium. The discrete regions of contact between
the chorion and the endometr ium form specific zones
of metabolic exchange. The placenta also produces
4. a variety of hormones . This endocrine function is
important for the maintenance of pregnancy and the
induction of parh1rition.
Parturition (giving birth to young) is the step
in the reproductive process that immediately precedes
lactation, uterine repair and return to cyclicity. It is
ini tiated by the feh1s and involves a complex cascade
of endocrine events that promote myometrial contrac-
tions, dilation of the cervix, expulsion of the feh1s and
expulsion of the extraembryonic membranes.
Placentas Have Different Distributions
of Chorionic Villi
As you have learned in the previous chapter, the
conceptus consists of the embryo and the extraembry-
onic membranes (amnion, allantois and chorion). The
chorion is the fetal contribution to the placenta. The
functional uni t of the fetal placenta is the chorionic
villus. The chorionic villus is an "exchange apparatus"
and provides increased surface area so that exchange
is maximized. Chorionic villi are small, finger- like
projections that are on the surface of the chorion. These
tiny villi protrude away from the chorion toward the
uterine endometrium. Placentas are classified according
to the distribution of chorionic vill i on their surfaces,
Ve
tB
oo
ks
.ir
5. The Puerperium & Lactation
Early Embryogenesis &
Maternal Recognition of Pregnancy
Ovulation & Fertilization
Cyclicity
Regulation of
Reproduction
Tract Function
Puberty
Prenatal
Development
Spermatogenesis
Regulat ion of
Reproduction
Tract Function
Puberty
Prenatal
Development
Take Home Message
Gestation is the period of time that a female is pregnant. During
gestation, the
placenta forms a major organ of pregnancy that provides an
6. inteJface for metabolic
exchange between the dam and the f etus. Placentas are
described mmplwlogically
according to the distribution of villi on the chorionic smface
ami the degree of separa..:.
tion between matemal and fetal blood. The placenta is also an
endocrine organ that
secretes hormones responsible for: 1) maintenance of
pregnancy; 2) stimulation of the
matemal mammmy gland and 3) ensures fetal growth.
Parturition is brought about
by secretion of fetal corticoitls and requires removal of the
progesterone block. Par-
turition consists of three stages. They are: 1) initiation of
myometrial contractions;
2) expulsion ofthe f etus and 3) e.::pulsion
oftlzefetalmembranes.
The word gestation literally means "the act
of carry ing or being carried". Thus, gestation means
the action or process of carrying or being carried' in
the uterus between conception and birth . · Gest ation
and pregnancy are synonymous and thus, gestation
length means the length of pregnancy. Attachment
of the conceph1s to form an intimate, but temporary,
relationship with the uterus is an evolutionary step that
provides significant advantage to the conceph1s . The
phenomenon of intrauterine development ensures that
the developing conceptus will receive adequate nutri-
tion and protection during its development. In contrast,
lower fon11S of animals lay eggs (oviparous). The
survival of potential offspring of oviparous animals
is jeopardized because the female cannot completely
protect the eggs from environmental and predatmy dan-
ger. Thus, from an evolutionary perspective, eutherian
mammals (mammals with a placenta), are "equipped"
7. with an in-utero protection mechanism that is highly
successful after the placenta is formed.
The final prepartum steps of
reproduction are:
• formation of a placenta
• acquisition of endocrine function of
the placenta
• initiation of parturition
The term implantation is often used to mean
attachment of the placental membranes to the endo-
metrium in most animals. Achmlly, true implantation
is a phenomenon in humans in which the conceptus
"buries" itself into the uterine endometrium. The con-
ceptus temporarily disappears beneath the surface. In
most other species, the conceph1s does not truly implant,
but rather attaches to the endometrial surface and never
disappears from the luminal compartment.
The placenta is an organ of metabolic inter-
change between the conceph1s and the dam. It is also
an endocrine organ. The placenta is composed of a fetal
component derived fi·om the chorion and a maternal
component derived from modifications of the uterine
endometrium. The discrete regions of contact between
the chorion and the endometr ium form specific zones
of metabolic exchange. The placenta also produces
a variety of hormones . This endocrine function is
important for the maintenance of pregnancy and the
induction of parh1rition.
8. Parturition (giving birth to young) is the step
in the reproductive process that immediately precedes
lactation, uterine repair and return to cyclicity. It is
ini tiated by the feh1s and involves a complex cascade
of endocrine events that promote myometrial contrac-
tions, dilation of the cervix, expulsion of the feh1s and
expulsion of the extraembryonic membranes.
Placentas Have Different Distributions
of Chorionic Villi
As you have learned in the previous chapter, the
conceptus consists of the embryo and the extraembry-
onic membranes (amnion, allantois and chorion). The
chorion is the fetal contribution to the placenta. The
functional uni t of the fetal placenta is the chorionic
villus. The chorionic villus is an "exchange apparatus"
and provides increased surface area so that exchange
is maximized. Chorionic villi are small, finger- like
projections that are on the surface of the chorion. These
tiny villi protrude away from the chorion toward the
uterine endometrium. Placentas are classified according
to the distribution of chorionic vill i on their surfaces,
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294 Placentation, Gestation and Parturition
giving each placental type a distinct anatomical appear-
ance. Placentas may also be classified by number of
9. tissue layers separating maternal and fetal blood.
Placentas are classified acc01·ding to the
distribution of chorionic viili. These
classifications are:
• diffuse
• zonary
• discoid
• cotyledonary
The diffi.tse placenta of the pig has a velvet-like
surface with many closely spaced chorionic villi that are
distributed over the entire surface of the chorion (See
Figure 14-1 ). Initial attachment occurs around day 12
and is well established by day 18 to 20 after ovulation
(See Chapter 13).
Diffuse placentas have uniform
distribution of chorionic villi that
cover the swface of the chorion.
Example= pig
The mare placenta is also classified as diffuse,
however it is characterized by having many specialized
"microzones" of chorionic villi known as microcoty-
ledons (See Figure 14-1 ). These microcotyledons are
microscopically discrete regions at the fetal-maternal
interface. As in the pig, they are also distributed over
the entire chorionic surface.
The mare placenta also contains unique tran-
sitory structures known as endometrial cups. These
are discrete areas that range from a few millimeters
to several centimeters in diameter. The endometrial
10. cups are of both trophoblastic and endometrial origin.
There are 5 to I 0 endometrial cups distributed over the
surface of the placenta (See Figure 14-6). Endometrial
cups produce equine chorionic gonadotropin (eCG)
and develop between days 35 and 60 of pregnancy.
Following day 60, the endometrial cups are sloughed
into the uterine lumen and are no longer functional.
Attachment of the conceptus to the endometrium is
initiated at about day 24 and becomes well established
by 36 to 38 days (See Chapter 13).
Zonary placentas have a band-like
zone of chorionic villi.
Example = dogs and cats
The zonary placenta (found in dogs and cats)
includes a prominent region of exchange that fonns
a broad zone around the chorion near the middle of
the conceptus (See F igure 14-2). A second region
consists of a highly pigmented ring at either end of the
central zone. This pigmented zone consists of small
hematomas (blood clots). The pigmented zone is also
refetTed to as the paraplacenta and is thought to be
important in iron transport from the dam to the fehts.
The function of this zone is not well understood. A
third region is the transparent zone on the distal ends
of the chorion that has poor vascularity. This zone may
be involved in absorption of materials directly from the
uterine lumen.
Discoid placentas form a
regionalized disc.
Example = rodents and primates
11. The discoid placenta (See Figure 14-2) is found
in rodents and primates. It is characterized by having
one or two distinct adj acent discs. These discs contain
chorionic vi lli that interface with the endometrium
and provide the region for gas, nutrient and metabolic
waste exchange.
Cotyledonary placentas have nu-
merous, discrete button-like
structures called cotyledons.
Example = ruminants
Ruminants have a cotyledonary placenta (See
Figure 14-3). A cotyledon is defined as a placental
unit of trophoblastic origin cons isting of abundant
blood vessels and connective tissue. In sheep, there
are between 90 and 100 cotyledons distributed across
the surface of the chorion and, in cattle, 70 to 120
cotyledons have been observed. The placentome (point
of interface) in the cotyledonary placenta consists of
a fetal cotyledon contributed by the chorion and a
maternal cotyledon , originating from the caruncular
regions of the u terus. At about day 16 in sheep and
day 25 in cattle the chorion initiates attachment to the
cm·uncles of the uterus. Prior to this time the placenta
is essentially diffi.tse. During the formation of the
placentomes, chorionic v illi protrude into crypts in the
caruncular tissue. This relationship .lli not implantation
but an anatomically specialized forn1 of attachment.
Attachment is well established by day 30 in ewes and
day 40 in cows (See Chapter 13).
In the cow, the placentomes form a convex
structure, whi le in the ewe they are concave (See
Figure 14-3). During gestation, the cotyledons will
12. increase many-fold in diameter. In fact, cotyledons in
the cow near the end of gestation may measure 5 to
6 centimeters in diameter. Such growth provides
enormous surface area to support placental transfer
of nutrients from the dam and metabolic wastes from
the fetus.
Placental Classification by Microscopic
Appearance is Based on the Number of
Placental Layers that Separate the Fetal
Blood from the Maternal Blood
The nomenclature for describing placental in-
timacy is derived by first describing the tissues of the
maternal placenta in the prefix of the word. The tissues
of the fetal placenta constitute the suffix. Exchange can
occur through as many as six tissue layers and as few
as three. The name of the prefix and suffix of each type
of placenta changes depending on the number of tissue
layers that exist.
Prefix =maternal side Suffix =fetal side
"epithelia" "chorial"
epitheliochorial
Placentation, Gestation and Parturition 295
cells originate from trophoblast cells and are thotwht
to be fanned continuously throughout gestation. Bi-
nucleate giant cells constitute around 20% of the fetal
placenta. During development, the binucleate giant
cells migrate from the chorionic epithelium and invade
the endometrial epithelium (See Figure 14-4). The
13. binucleate giant cells are believed to transfer complex
molecules from the fetal to the maternal p lacenta.
There is evidence that they secrete placental lactogen.
Also, these cells secrete pregnancy specific protein
B (PSPB) that are also called pregnancy associated
glycoproteins (PAG). These proteins are unique to
pregnancy in ruminants. The binucleate giant cells
are also important sites of steroidogenesis, secreting
progesterone and estradiol. These cells will no doubt
emerge as increasingly important "players" in the func-
tion of the ruminant placenta with further research.
I Endotheliochorial = 5 layers I
The endotheliochorial placenta is character-
ized as having complete erosion of the endometrial
epithelium and underlying interstitium. T hus, maternal
capillaries are directly exposed to epithelial cells of the
chorion (See Figure 14-5). The chorionic epithelium
packs around the vessels on the maternal side. Note in
Figure 14-5 that this type of placenta is more intimate
I Epitheliochorial 6 layers I than the epitheliochoriat placenta
because the en dome-- _ trial epithelium no longer exists. Dogs
and cats possess ..__ _ _ ____ _ _ _ _____ ____ _.
endotheliochorial placentation.
The epitheliochorial placenta (See Figure
14-5) is the least intimate among the placental types.
In the epitheliochorial placenta, both the endometrial
epithelium (maternal side) and epithelium of the chori-
onic villi are intact. In other words, there is a complete
intact layer of epithelium in both the maternal and fetal
components. The epitheliochorial placenta is found in
the sow and the mare. Recall that the placentas of the
sow and the mare are diffitse and villi occupy a large
14. proportion of the surface area of the chorion.
Ruminants also have an epitheliochorial pla-
centa. However, the endometrial epithelium transiently
erodes and then regrows, causing intennittent exposure
of the maternal capillaries to the chorionic epithelium.
This type of placenta has been tenned syndesmocho-
rial.
In addition to the feature of partial erosion
of the endometrial epithelium, a unique cell type is
found in the ruminant placenta. These cells are called
binucleate giant cells. As their name implies, they are
characterized as being quite large and have two nuclei.
Binucleate giant cells appear at about day 14 in the
sheep and between days 18 and 20 in the cow. These
I Hemochorial = 3 layers I
The hemochorial placenta (See Figure 14-5)
is characterized as having the chorionic epithelium in
direct apposition to maternal pools ofblood. Thus, nu-
trients and gases are exchanged directly from maternal
blood and must move tlu-ough only tlu-ee tissue layers.
This highly intimate relationship is found in primates
and rodents (See Figure 14-5).
The Placenta Regulates the Exchange
Between the Fetus and Dam
Placental exchange involves a number of
mechanisms found in other tissues. These are simple
diffusion, facilitated diffusion and active tr a nsport.
Gases and water pass from high to low concentrations
by simple diffusion. The p lacenta contains act ive
transport pumps for sodium and potassium, as well as
15. calcium. Glucose and other metabolically important
materials such as amino acids are transported by facili-
tated di ffusion uti lizing specific carrier molecules.
141
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294 Placentation, Gestation and Parturition
giving each placental type a distinct anatomical appear-
ance. Placentas may also be classified by number of
tissue layers separating maternal and fetal blood.
Placentas are classified acc01·ding to the
distribution of chorionic viili. These
classifications are:
• diffuse
• zonary
• discoid
• cotyledonary
The diffi.tse placenta of the pig has a velvet-like
surface with many closely spaced chorionic villi that are
distributed over the entire surface of the chorion (See
Figure 14-1 ). Initial attachment occurs around day 12
and is well established by day 18 to 20 after ovulation
(See Chapter 13).
16. Diffuse placentas have uniform
distribution of chorionic villi that
cover the swface of the chorion.
Example= pig
The mare placenta is also classified as diffuse,
however it is characterized by having many specialized
"microzones" of chorionic villi known as microcoty-
ledons (See Figure 14-1 ). These microcotyledons are
microscopically discrete regions at the fetal-maternal
interface. As in the pig, they are also distributed over
the entire chorionic surface.
The mare placenta also contains unique tran-
sitory structures known as endometrial cups. These
are discrete areas that range from a few millimeters
to several centimeters in diameter. The endometrial
cups are of both trophoblastic and endometrial origin.
There are 5 to I 0 endometrial cups distributed over the
surface of the placenta (See Figure 14-6). Endometrial
cups produce equine chorionic gonadotropin (eCG)
and develop between days 35 and 60 of pregnancy.
Following day 60, the endometrial cups are sloughed
into the uterine lumen and are no longer functional.
Attachment of the conceptus to the endometrium is
initiated at about day 24 and becomes well established
by 36 to 38 days (See Chapter 13).
Zonary placentas have a band-like
zone of chorionic villi.
Example = dogs and cats
The zonary placenta (found in dogs and cats)
includes a prominent region of exchange that fonns
17. a broad zone around the chorion near the middle of
the conceptus (See F igure 14-2). A second region
consists of a highly pigmented ring at either end of the
central zone. This pigmented zone consists of small
hematomas (blood clots). The pigmented zone is also
refetTed to as the paraplacenta and is thought to be
important in iron transport from the dam to the fehts.
The function of this zone is not well understood. A
third region is the transparent zone on the distal ends
of the chorion that has poor vascularity. This zone may
be involved in absorption of materials directly from the
uterine lumen.
Discoid placentas form a
regionalized disc.
Example = rodents and primates
The discoid placenta (See Figure 14-2) is found
in rodents and primates. It is characterized by having
one or two distinct adj acent discs. These discs contain
chorionic vi lli that interface with the endometrium
and provide the region for gas, nutrient and metabolic
waste exchange.
Cotyledonary placentas have nu-
merous, discrete button-like
structures called cotyledons.
Example = ruminants
Ruminants have a cotyledonary placenta (See
Figure 14-3). A cotyledon is defined as a placental
unit of trophoblastic origin cons isting of abundant
blood vessels and connective tissue. In sheep, there
are between 90 and 100 cotyledons distributed across
18. the surface of the chorion and, in cattle, 70 to 120
cotyledons have been observed. The placentome (point
of interface) in the cotyledonary placenta consists of
a fetal cotyledon contributed by the chorion and a
maternal cotyledon , originating from the caruncular
regions of the u terus. At about day 16 in sheep and
day 25 in cattle the chorion initiates attachment to the
cm·uncles of the uterus. Prior to this time the placenta
is essentially diffi.tse. During the formation of the
placentomes, chorionic v illi protrude into crypts in the
caruncular tissue. This relationship .lli not implantation
but an anatomically specialized forn1 of attachment.
Attachment is well established by day 30 in ewes and
day 40 in cows (See Chapter 13).
In the cow, the placentomes form a convex
structure, whi le in the ewe they are concave (See
Figure 14-3). During gestation, the cotyledons will
increase many-fold in diameter. In fact, cotyledons in
the cow near the end of gestation may measure 5 to
6 centimeters in diameter. Such growth provides
enormous surface area to support placental transfer
of nutrients from the dam and metabolic wastes from
the fetus.
Placental Classification by Microscopic
Appearance is Based on the Number of
Placental Layers that Separate the Fetal
Blood from the Maternal Blood
The nomenclature for describing placental in-
timacy is derived by first describing the tissues of the
maternal placenta in the prefix of the word. The tissues
of the fetal placenta constitute the suffix. Exchange can
19. occur through as many as six tissue layers and as few
as three. The name of the prefix and suffix of each type
of placenta changes depending on the number of tissue
layers that exist.
Prefix =maternal side Suffix =fetal side
"epithelia" "chorial"
epitheliochorial
Placentation, Gestation and Parturition 295
cells originate from trophoblast cells and are thotwht
to be fanned continuously throughout gestation. Bi-
nucleate giant cells constitute around 20% of the fetal
placenta. During development, the binucleate giant
cells migrate from the chorionic epithelium and invade
the endometrial epithelium (See Figure 14-4). The
binucleate giant cells are believed to transfer complex
molecules from the fetal to the maternal p lacenta.
There is evidence that they secrete placental lactogen.
Also, these cells secrete pregnancy specific protein
B (PSPB) that are also called pregnancy associated
glycoproteins (PAG). These proteins are unique to
pregnancy in ruminants. The binucleate giant cells
are also important sites of steroidogenesis, secreting
progesterone and estradiol. These cells will no doubt
emerge as increasingly important "players" in the func-
tion of the ruminant placenta with further research.
I Endotheliochorial = 5 layers I
The endotheliochorial placenta is character-
ized as having complete erosion of the endometrial
epithelium and underlying interstitium. T hus, maternal
capillaries are directly exposed to epithelial cells of the
20. chorion (See Figure 14-5). The chorionic epithelium
packs around the vessels on the maternal side. Note in
Figure 14-5 that this type of placenta is more intimate
I Epitheliochorial 6 layers I than the epitheliochoriat placenta
because the en dome-- _ trial epithelium no longer exists. Dogs
and cats possess ..__ _ _ ____ _ _ _ _____ ____ _.
endotheliochorial placentation.
The epitheliochorial placenta (See Figure
14-5) is the least intimate among the placental types.
In the epitheliochorial placenta, both the endometrial
epithelium (maternal side) and epithelium of the chori-
onic villi are intact. In other words, there is a complete
intact layer of epithelium in both the maternal and fetal
components. The epitheliochorial placenta is found in
the sow and the mare. Recall that the placentas of the
sow and the mare are diffitse and villi occupy a large
proportion of the surface area of the chorion.
Ruminants also have an epitheliochorial pla-
centa. However, the endometrial epithelium transiently
erodes and then regrows, causing intennittent exposure
of the maternal capillaries to the chorionic epithelium.
This type of placenta has been tenned syndesmocho-
rial.
In addition to the feature of partial erosion
of the endometrial epithelium, a unique cell type is
found in the ruminant placenta. These cells are called
binucleate giant cells. As their name implies, they are
characterized as being quite large and have two nuclei.
Binucleate giant cells appear at about day 14 in the
sheep and between days 18 and 20 in the cow. These
I Hemochorial = 3 layers I
21. The hemochorial placenta (See Figure 14-5)
is characterized as having the chorionic epithelium in
direct apposition to maternal pools ofblood. Thus, nu-
trients and gases are exchanged directly from maternal
blood and must move tlu-ough only tlu-ee tissue layers.
This highly intimate relationship is found in primates
and rodents (See Figure 14-5).
The Placenta Regulates the Exchange
Between the Fetus and Dam
Placental exchange involves a number of
mechanisms found in other tissues. These are simple
diffusion, facilitated diffusion and active tr a nsport.
Gases and water pass from high to low concentrations
by simple diffusion. The p lacenta contains act ive
transport pumps for sodium and potassium, as well as
calcium. Glucose and other metabolically important
materials such as amino acids are transported by facili-
tated di ffusion uti lizing specific carrier molecules.
141
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296 Placentation, Gestation and Parturition
22. Figure 14-1. The Diffuse Placenta
Sow
r
Endometrium
=---
The diffuse placenta of the sow consists of
many chorionic villi distributed over the entire
surface of the chorion. They penetrate into
the endometrium forming the fetal-maternal
interface. Vessels from each chorionic vil-
lus merge and eventually form large vessels
that enter the umbilical cord. A= Allantois,
AC= Allantochorion, AM= Amnionic Cavity,
E= Endometrium, M= Myometrium
Mare
Endometrium
Myometrium
The diffuse placenta of the mare consists
of many microcotyledons distributed over
the entire surface of the chorion. These mi-
crocotyledons are the site of fetal-maternal
exchange. A= Allantois, AC= Allantochorion,
AM= Amnionic Cavity, E= Endometrium,
M= Myometrium, YS= Yolk Sac
Placentation, Gestation and Parturition 297
23. Figure 14-2. The Zonary and Discoid Placentas
AC
YS .....-"'
PZ
Bitch
The zonary placenta consists of three distinct zones;
a transfer zone (TZ), a pigmented zone (PZ) and a
relatively nonvascular zone, the allantochorion (AC).
In the zonary placenta, a band of tissue forms around
the conceptus where nutrient transfer occurs. The
pigmented zone (PZ) or paraplacenta represents local
regions of maternal hemorrhage and necrosis.
A= Allantois, AC= Allantochorion, AM= Amnionic Cavity,
E= Endometrium, M= Myometrium, YS= Yolk Sac
Primates
The discoid placenta consists of a round patch of chori-
onic tissue that forms the fetal-maternal interface. Ves-
sels from the exchange zone merge to form the umbilical
vessels that supply the fetus with blood. The vasculature
of the chorion (within the disc) is immersed in pools of
blood where metabolic exchange takes place.
A= Allantois, AC = Allantochorion,
AM= Amnionic Cavity, E = Endometrium,
EZ = Exchange Zone, M = Myometrium
14
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296 Placentation, Gestation and Parturition
Figure 14-1. The Diffuse Placenta
Sow
r
Endometrium
=---
The diffuse placenta of the sow consists of
many chorionic villi distributed over the entire
surface of the chorion. They penetrate into
the endometrium forming the fetal-maternal
interface. Vessels from each chorionic vil-
lus merge and eventually form large vessels
that enter the umbilical cord. A= Allantois,
AC= Allantochorion, AM= Amnionic Cavity,
E= Endometrium, M= Myometrium
Mare
Endometrium
Myometrium
25. The diffuse placenta of the mare consists
of many microcotyledons distributed over
the entire surface of the chorion. These mi-
crocotyledons are the site of fetal-maternal
exchange. A= Allantois, AC= Allantochorion,
AM= Amnionic Cavity, E= Endometrium,
M= Myometrium, YS= Yolk Sac
Placentation, Gestation and Parturition 297
Figure 14-2. The Zonary and Discoid Placentas
AC
YS .....-"'
PZ
Bitch
The zonary placenta consists of three distinct zones;
a transfer zone (TZ), a pigmented zone (PZ) and a
relatively nonvascular zone, the allantochorion (AC).
In the zonary placenta, a band of tissue forms around
the conceptus where nutrient transfer occurs. The
pigmented zone (PZ) or paraplacenta represents local
regions of maternal hemorrhage and necrosis.
A= Allantois, AC= Allantochorion, AM= Amnionic Cavity,
E= Endometrium, M= Myometrium, YS= Yolk Sac
Primates
The discoid placenta consists of a round patch of chori-
onic tissue that forms the fetal-maternal interface. Ves-
sels from the exchange zone merge to form the umbilical
26. vessels that supply the fetus with blood. The vasculature
of the chorion (within the disc) is immersed in pools of
blood where metabolic exchange takes place.
A= Allantois, AC = Allantochorion,
AM= Amnionic Cavity, E = Endometrium,
EZ = Exchange Zone, M = Myometrium
14
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298 Placentation, Gestation and Parturition
Figure 14-3. The Cotyledonary Placenta
Convex
(cow, giraffe)
In the photograph above, the fetal membranes and
the fetal cotyledons (FC) can be visualized. The
membrane labeled AC is the allantochorion. The
umbilical cord, (UC-arrow) of the fetus receives
blood vessels (BV) from the fetal cotyledons (FC).
Glycogen plaques (GP) can be visualized on the
surface of the chorion and the amnion. These
plaques are localized squamous proliferations
called verrucae.
27. Concave
(sheep, goat)
The cotyledonary placenta is characterized by numerous
"button-like" structures distributed across the surface
of the chorion . These are called fetal cotyledons. When they jo
in with the maternal caruncle they form a
placentome. Aconvex cotyledon becomes covered with the
chorion. Many finger-like villi (red) originating
from the chorionic tissue protrude toward the lumen of the
uterus. In the concave cotyledon, the chorionic
tissue pushes inward, forming a concave interface between the
chorion and the maternal caruncle.
Placentation, Gestation and Parturition 299
Figure 14-3. The Cotyledonary Placenta
The diagram in the upper left illustrates the distribution
of the extraembryonic membranes prior to complete at-
tachment. The extraembryonic membranes consist of the
amnion (blue sac), yolk sac (YS) and the allantois (A).
Even though the fetus is located in one uterine horn, the
chorion invades the contralateral uterine horn and forms
placentomes.
Cow
Some fetal cotyledons (FC) have been partially separated
from maternal cotyledons (MC). The chorion (C) is the
outer fetal membrane. Arrows indicate the border of the
amnion (A). The myometrium (M) is indicated by the ar-
rows. Notice that the fetal cotyledon (FC) is attached to
the surface of the caruncle creating a convex cotyledon.
E= Endometrium
28. Ewe-A
The chorion can be seen entering the placentome (P).
The chorionic stalk (CS) contains the fetal vasculature.
Ewe-8
)
A portion of the chorion has been incised so that the fetal
vasculature can be visualized clearly. The fetal vessels
(arrow) and chorionic tissue "push" into the caruncular
tissue forming a concave cotyledon. A set of arteries (A)
and veins (V) emerge from each cotyledon and eventually
merge in the umbilical cord (UC). P= Placentoma
Ewe-C
A concave placentoma is clearly visible. The chorionic
stalk is draped over the needle holder. Notice the vessels
(arrows) within the chorionic tissue. The reddish-beige
tissue is the maternal cotyledon (MC) that is covered by
the allantochorion. The dark tissue in the center (arrows)
is the fetal component of the placentome.
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298 Placentation, Gestation and Parturition
Figure 14-3. The Cotyledonary Placenta
29. Convex
(cow, giraffe)
In the photograph above, the fetal membranes and
the fetal cotyledons (FC) can be visualized. The
membrane labeled AC is the allantochorion. The
umbilical cord, (UC-arrow) of the fetus receives
blood vessels (BV) from the fetal cotyledons (FC).
Glycogen plaques (GP) can be visualized on the
surface of the chorion and the amnion. These
plaques are localized squamous proliferations
called verrucae.
Concave
(sheep, goat)
The cotyledonary placenta is characterized by numerous
"button-like" structures distributed across the surface
of the chorion . These are called fetal cotyledons. When they jo
in with the maternal caruncle they form a
placentome. Aconvex cotyledon becomes covered with the
chorion. Many finger-like villi (red) originating
from the chorionic tissue protrude toward the lumen of the
uterus. In the concave cotyledon, the chorionic
tissue pushes inward, forming a concave interface between the
chorion and the maternal caruncle.
Placentation, Gestation and Parturition 299
Figure 14-3. The Cotyledonary Placenta
The diagram in the upper left illustrates the distribution
of the extraembryonic membranes prior to complete at-
tachment. The extraembryonic membranes consist of the
amnion (blue sac), yolk sac (YS) and the allantois (A).
30. Even though the fetus is located in one uterine horn, the
chorion invades the contralateral uterine horn and forms
placentomes.
Cow
Some fetal cotyledons (FC) have been partially separated
from maternal cotyledons (MC). The chorion (C) is the
outer fetal membrane. Arrows indicate the border of the
amnion (A). The myometrium (M) is indicated by the ar-
rows. Notice that the fetal cotyledon (FC) is attached to
the surface of the caruncle creating a convex cotyledon.
E= Endometrium
Ewe-A
The chorion can be seen entering the placentome (P).
The chorionic stalk (CS) contains the fetal vasculature.
Ewe-8
)
A portion of the chorion has been incised so that the fetal
vasculature can be visualized clearly. The fetal vessels
(arrow) and chorionic tissue "push" into the caruncular
tissue forming a concave cotyledon. A set of arteries (A)
and veins (V) emerge from each cotyledon and eventually
merge in the umbilical cord (UC). P= Placentoma
Ewe-C
A concave placentoma is clearly visible. The chorionic
stalk is draped over the needle holder. Notice the vessels
(arrows) within the chorionic tissue. The reddish-beige
tissue is the maternal cotyledon (MC) that is covered by
the allantochorion. The dark tissue in the center (arrows)
is the fetal component of the placentome.
31. Ve
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300 Placentation, Gestation and Parturition
Glucose is the major source of energy for the
fetus. The majority of glucose is derived from the ma-
temal circulation. Near the end of gestation, glucose
consumption by the fetus is exceptionally high and
can lead to a metabolic drain of glucose away from the
dam. Such a glucose drain favors the development of
ketosis in the dam. Ketosis results from the metabo-
lism of body fat that generate ketones for energy when
glucose is limited. Periparturient ketosis is common
in dairy cows where postpartum metabolic demands
are exceptionally high because of high milk produc-
tion. Some materials cannot be transported across the
placenta. With the exception of some immunoglobu-
lins, matemal proteins do not cross the placental banier.
Immunoglobulins can be transported from the matemal
to the fetal side in a hemochorial or an endotheliochorial
placenta. However, the fetus synthesizes the majority
of its own proteins from amino acids contributed by
the dam. Nutritionally-based lipids do not cross the
placenta. Instead, the placenta hydrolyzes triglycer-
ides and matemal phospholipids and synthesizes new
lipid materials to be used by the fetus. Large peptide
honnones such as thyroid stimulating hom1one, adrenal
cortical stimulating hormone, growth honnone, insu-
lin and glucagon do not cross the placenta. Smaller
molecular weight hormones such as steroids, thyroid
32. hormone and the catecholamines (epinephrine and
norepinephrine) cross the placenta with relative ease.
Vitamins and minerals are transfened to the fetus at
variable rates. Fat soluble vitamins do not cross the
placenta with ease, while water soluble vitamins (Band
K) pass across the placenta with relative ease. Nutrients
are also transferred by pinocytosis and phagocytosis.
Areolae from the chorion form over the openings of
the uterine glands and are thought to absorb secretions
from these glands.
Of significant importance is the ability of the
placenta to transfer toxic and potentially pathogenic ma-
terials. Many toxic substances easily cross the placental
banier. These include ethyl alcohol, lead, phosphorus
and mercmy. Also, opiate drugs and numerous common
phmmaceuticals such as barbiturates and antibiotics can
cross the placental banier. Some substances may be
highly teratogenic. Teratogenic means inducing ab-
normal development (birth defects). These substances
include LSD, amphetamines, lithium, diethylstilbestrol
and thalidomide. It is well documented that these ma-
terials induce abnormal embtyonic development and
cause serious birth defects.
It is known that a wide range of microorgan-
isms can contaminate the fetus. Viruses can cross the
placental banier with ease and thus many viral diseases
can be transmitted from the dam to the fetus. Such
human diseases as German measles, Herpes virus and
HIV can be transmitted from the pregnant mother to the
fetus. Bacteria such as syphilis can also be transmitted
to the fetus.
Figure 14-4. The Migration of Binucleate Giant Cells
33. in the Ruminant Placenta
r::
Fetal
(chorion)
Maternal
(endometrial
epithelium)
Basement membrane
Maternal circulation
Binucleate giant cells
(BNGC) migrate from
the chorion to the en-
dometrial epithelium
in ruminants. These
cells are thought to se-
crete placental lactogen
and pregnancy specific
protein B.
(www. biotracking. com)
Placentation, Gestation and Parturition 301
Figure 14-5. Placental Classification Based on Separation
Between Fetal and Maternal Blood Supplies
Fetal
(chorion)
Maternal
35. Hemochorial
(primates and rodents)
3. Chorionic capillaries
2. Chorionic interstitium
1. Chorionic epithelium
RBC= Red blood cell
Ve
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300 Placentation, Gestation and Parturition
Glucose is the major source of energy for the
fetus. The majority of glucose is derived from the ma-
temal circulation. Near the end of gestation, glucose
consumption by the fetus is exceptionally high and
can lead to a metabolic drain of glucose away from the
dam. Such a glucose drain favors the development of
ketosis in the dam. Ketosis results from the metabo-
lism of body fat that generate ketones for energy when
glucose is limited. Periparturient ketosis is common
in dairy cows where postpartum metabolic demands
are exceptionally high because of high milk produc-
tion. Some materials cannot be transported across the
placenta. With the exception of some immunoglobu-
lins, matemal proteins do not cross the placental banier.
Immunoglobulins can be transported from the matemal
to the fetal side in a hemochorial or an endotheliochorial
placenta. However, the fetus synthesizes the majority
36. of its own proteins from amino acids contributed by
the dam. Nutritionally-based lipids do not cross the
placenta. Instead, the placenta hydrolyzes triglycer-
ides and matemal phospholipids and synthesizes new
lipid materials to be used by the fetus. Large peptide
honnones such as thyroid stimulating hom1one, adrenal
cortical stimulating hormone, growth honnone, insu-
lin and glucagon do not cross the placenta. Smaller
molecular weight hormones such as steroids, thyroid
hormone and the catecholamines (epinephrine and
norepinephrine) cross the placenta with relative ease.
Vitamins and minerals are transfened to the fetus at
variable rates. Fat soluble vitamins do not cross the
placenta with ease, while water soluble vitamins (Band
K) pass across the placenta with relative ease. Nutrients
are also transferred by pinocytosis and phagocytosis.
Areolae from the chorion form over the openings of
the uterine glands and are thought to absorb secretions
from these glands.
Of significant importance is the ability of the
placenta to transfer toxic and potentially pathogenic ma-
terials. Many toxic substances easily cross the placental
banier. These include ethyl alcohol, lead, phosphorus
and mercmy. Also, opiate drugs and numerous common
phmmaceuticals such as barbiturates and antibiotics can
cross the placental banier. Some substances may be
highly teratogenic. Teratogenic means inducing ab-
normal development (birth defects). These substances
include LSD, amphetamines, lithium, diethylstilbestrol
and thalidomide. It is well documented that these ma-
terials induce abnormal embtyonic development and
cause serious birth defects.
It is known that a wide range of microorgan-
37. isms can contaminate the fetus. Viruses can cross the
placental banier with ease and thus many viral diseases
can be transmitted from the dam to the fetus. Such
human diseases as German measles, Herpes virus and
HIV can be transmitted from the pregnant mother to the
fetus. Bacteria such as syphilis can also be transmitted
to the fetus.
Figure 14-4. The Migration of Binucleate Giant Cells
in the Ruminant Placenta
r::
Fetal
(chorion)
Maternal
(endometrial
epithelium)
Basement membrane
Maternal circulation
Binucleate giant cells
(BNGC) migrate from
the chorion to the en-
dometrial epithelium
in ruminants. These
cells are thought to se-
crete placental lactogen
and pregnancy specific
protein B.
(www. biotracking. com)
38. Placentation, Gestation and Parturition 301
Figure 14-5. Placental Classification Based on Separation
Between Fetal and Maternal Blood Supplies
Fetal
(chorion)
Maternal
(endometrial
epithelium)
Fetal
(chori on)
Fetal
(chorion)
Maternal
(endometrium)
Epitheliochorial
Endotheliochorial
Hemochorial
Epithel iochorial
(pigs, horses and ruminants)
6. Chorionic capillaries
5. Chorionic interstitium
4. Chorionic epithelium
3. Endometrial epithelium
2. Endometrial interstitium
1. Endometrial capillaries
39. Endotheliochorial
(dogs and cats)
5. Chorionic capillaries
4. Chorionic interstitium
3. Chorionic epithelium
2. Endometrial interstitium
1. Endometrial capillaries
Hemochorial
(primates and rodents)
3. Chorionic capillaries
2. Chorionic interstitium
1. Chorionic epithelium
RBC= Red blood cell
Ve
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302 Placentation, Gestation and Parturition
The Placenta is a Major Endocrine Organ
During Pregnancy
In addition to serving as a metabolic exchange
organ, the placenta serves as a transitory endocrine or-
gan. Hormones from the placenta gain access to both
the fetal and the matemal circulation.
40. The placenta secretes hormones that can:
• stimulate ovarian function
• maintain pregnancy
• influence fetal growth
• stimulate mammary function
• assist in parturition
The placenta of the mare produces a gonado-
tropin called equine chorionic gonadotropin (eCG).
Equine chorionic gonadotropin is also called pregnant
mare's serum gonadotropin (PMSG). Equine cho-
rionic gonadotropin is produced by the endometrial
cups of the placenta. Endomeh·ial cups are a transient
placental endocrine gland. They begin producing eCG
at the time of attachment of the conceptus to the endo-
metrium. The relationship between the fom1ation of
the endometrial cups in the mare and the synthesis of
eCG is presented in Figure 14-6. As you can see, the
production of eCG is closely related to the weight of
the endometrial cups.
Equine chorionic gonadotropin acts as a lu-
teotropin and provides a stimulus for maintenance of the
primary cm·pus luteum. The primary corpus luteum
in the mare is defined as the corpus luteum fom1ed
from the ovulated follicle. In addition, eCG is respon-
sible for controlling the formation and maintenance of
supplementary (accessory) corpora lutca. As eCG
increases, the pregnant mare will often ovulate, thus
generating accessory corpora lutea. The eCG-induced
ovulations occur between days 40 and 70 of preg-
nancy. Luteinization (promoted by eCG) also occurs
in antral follicles that do not ovulate. Thus, eCG has a
significant positive impact on the ability of the ovary
to produce progesterone. Indeed, if one examines the
41. progesterone profile, it can be seen that there is a close
relationship between the concentrations of proges-
terone and the production of accessory corpora lutea
(See Figure 14-7).
In addition to its luteotropic action, eCG has
powerful FSH-like actions when administered to fe-
males of other species. In fact, eCG will cause marked
follicular development in most species. It is used com-
monly to induce superovulation where embryo transfer
is performed (cow, sheep, rabbit). In mares, however,
eCG does not exert significant FSH-like action.
--'E
Db c .._,
l!l u
Cll
Figure 14-6. Production of
Equine Chorionic Gonadotropin
(eGG) is Closely Related to the
Weight of the
Endometrial Cups
(Modified from Ginther,
Reproductive Biologv of the Mare)
175 10
ISO 9
125 I 0
I
I
I 100 I 7
42. I
I
75 I 6 I
I
I
50 I 5
4 25 I ----
40 60 80 100 120 140 160 18 0 200
Days of Gestation
Endometrial cups (EC) are seen here in
a U-shaped configuration. The fetus (F)
is surrounded by the amnion (not visible).
The membrane indicated by arrows is the
allantochorion . This specimen was re-
moved from a mare at 50 days of gestation.
(Photograph courtesy of Dr. O.J. Ginther from Reproductive
Biology of the Mare. 2nd Ed.)
,...,
Ill a.
:I u
iii
'i: ...
Ill
E
0
'C c w ....
0
.....
J:
43. Placentation, Gestation and Parturition 303
Figure 14-7. Luteal Progesterone Output During the First Half
of Gestation in the Mare
(Modified from Ginther, Reproductive Biologv of the Mare)
Progesterone { P4) from the primary corpus
luteum increases rapidly after ovulation and
then decreases (hatched region) . Without
eCG, P4 would continue to decrease {dashed
line) and the pregnancy would terminate.
Ill c
0 -:p
ns
:1.. ns -4J c c
:1.. Cl)
Cl) u
-4J c ns 0 :ru
Cl) Cl)
> c ·.p 0 ns :1..
Q) Cl) -4J cc: Ill Cl)
b.O
0
:1..
Q.
' ,,
Upon stimulation by eCG, the primary CL is
stimulated and P4 in the maternal blood again
44. increases. If eCG were not produced, P4
would continue to decrease (dashed line).
As eCG continues to increase, accessory CL
develop and P4 increases until about day 100.
After day 100, the placenta assumes the
major P4 producing ro le.
0 30 60 90 120 ISO 180 2 10 240 270
Days of Gestation
Figure 14-8. The Production of hCG and Progesterone During
Gestation in the Pregnant Woman
Human chorionic gonadotropin peaks at about 2.5
months of gestation and then declines. This period of
time is critical for maintenance of pregnancy because
the corpus luteum assumes primary responsibility for
progesterone secretion.
Ovarian P4
hCG
2 3 4
At about 2 .5 to 3 months of the placenta
begins to assume the primary responsibility for proges-
terone secretion and continues this role until the time of
parturition . hCG increases slightly between months 6
and 9 because of the increased placental mass.
Parturition
Placental P4
45. 5 6 7 8 9
Months of Gestation
Ve
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302 Placentation, Gestation and Parturition
The Placenta is a Major Endocrine Organ
During Pregnancy
In addition to serving as a metabolic exchange
organ, the placenta serves as a transitory endocrine or-
gan. Hormones from the placenta gain access to both
the fetal and the matemal circulation.
The placenta secretes hormones that can:
• stimulate ovarian function
• maintain pregnancy
• influence fetal growth
• stimulate mammary function
• assist in parturition
The placenta of the mare produces a gonado-
tropin called equine chorionic gonadotropin (eCG).
Equine chorionic gonadotropin is also called pregnant
mare's serum gonadotropin (PMSG). Equine cho-
rionic gonadotropin is produced by the endometrial
cups of the placenta. Endomeh·ial cups are a transient
46. placental endocrine gland. They begin producing eCG
at the time of attachment of the conceptus to the endo-
metrium. The relationship between the fom1ation of
the endometrial cups in the mare and the synthesis of
eCG is presented in Figure 14-6. As you can see, the
production of eCG is closely related to the weight of
the endometrial cups.
Equine chorionic gonadotropin acts as a lu-
teotropin and provides a stimulus for maintenance of the
primary cm·pus luteum. The primary corpus luteum
in the mare is defined as the corpus luteum fom1ed
from the ovulated follicle. In addition, eCG is respon-
sible for controlling the formation and maintenance of
supplementary (accessory) corpora lutca. As eCG
increases, the pregnant mare will often ovulate, thus
generating accessory corpora lutea. The eCG-induced
ovulations occur between days 40 and 70 of preg-
nancy. Luteinization (promoted by eCG) also occurs
in antral follicles that do not ovulate. Thus, eCG has a
significant positive impact on the ability of the ovary
to produce progesterone. Indeed, if one examines the
progesterone profile, it can be seen that there is a close
relationship between the concentrations of proges-
terone and the production of accessory corpora lutea
(See Figure 14-7).
In addition to its luteotropic action, eCG has
powerful FSH-like actions when administered to fe-
males of other species. In fact, eCG will cause marked
follicular development in most species. It is used com-
monly to induce superovulation where embryo transfer
is performed (cow, sheep, rabbit). In mares, however,
eCG does not exert significant FSH-like action.
--'E
47. Db c .._,
l!l u
Cll
Figure 14-6. Production of
Equine Chorionic Gonadotropin
(eGG) is Closely Related to the
Weight of the
Endometrial Cups
(Modified from Ginther,
Reproductive Biologv of the Mare)
175 10
ISO 9
125 I 0
I
I
I 100 I 7
I
I
75 I 6 I
I
I
50 I 5
4 25 I ----
40 60 80 100 120 140 160 18 0 200
Days of Gestation
48. Endometrial cups (EC) are seen here in
a U-shaped configuration. The fetus (F)
is surrounded by the amnion (not visible).
The membrane indicated by arrows is the
allantochorion . This specimen was re-
moved from a mare at 50 days of gestation.
(Photograph courtesy of Dr. O.J. Ginther from Reproductive
Biology of the Mare. 2nd Ed.)
,...,
Ill a.
:I u
iii
'i: ...
Ill
E
0
'C c w ....
0
.....
J:
Placentation, Gestation and Parturition 303
Figure 14-7. Luteal Progesterone Output During the First Half
of Gestation in the Mare
(Modified from Ginther, Reproductive Biologv of the Mare)
Progesterone { P4) from the primary corpus
luteum increases rapidly after ovulation and
then decreases (hatched region) . Without
eCG, P4 would continue to decrease {dashed
line) and the pregnancy would terminate.
Ill c
49. 0 -:p
ns
:1.. ns -4J c c
:1.. Cl)
Cl) u
-4J c ns 0 :ru
Cl) Cl)
> c ·.p 0 ns :1..
Q) Cl) -4J cc: Ill Cl)
b.O
0
:1..
Q.
' ,,
Upon stimulation by eCG, the primary CL is
stimulated and P4 in the maternal blood again
increases. If eCG were not produced, P4
would continue to decrease (dashed line).
As eCG continues to increase, accessory CL
develop and P4 increases until about day 100.
After day 100, the placenta assumes the
major P4 producing ro le.
0 30 60 90 120 ISO 180 2 10 240 270
Days of Gestation
Figure 14-8. The Production of hCG and Progesterone During
Gestation in the Pregnant Woman
50. Human chorionic gonadotropin peaks at about 2.5
months of gestation and then declines. This period of
time is critical for maintenance of pregnancy because
the corpus luteum assumes primary responsibility for
progesterone secretion.
Ovarian P4
hCG
2 3 4
At about 2 .5 to 3 months of the placenta
begins to assume the primary responsibility for proges-
terone secretion and continues this role until the time of
parturition . hCG increases slightly between months 6
and 9 because of the increased placental mass.
Parturition
Placental P4
5 6 7 8 9
Months of Gestation
Ve
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14
51. 304 Placentation, Gestation and Parturition
The second major gonadotropin of placental
origin is human chorionic gonadotropin (hCG). This
hormone is not only found in the human but in many
other primates. Often hCG (and eCG) may simply be
referred to as "CG". It originates from the trophoblas-
tic cells of the chorion and is secreted as soon as the
blastocyst hatches from the zona pellucida. Human
chorionic gonadotropin can be detected in the blood
and urine of the pregnant woman as early as days 8 to
1 0 of gestation. It increases rapidly in the urine of the
pregnant woman, reaching a maximum value at about
2.5 months (See Figure 14-8). Its presence in the urine
constitutes the basis for over-the-counter pregnancy
diagnosis kits.
The primary role of hCG during early preg-
nancy is to provide a luteotropic stimulus for the
ovulatory corpus luteum as it transitions into the CL of
pregnancy. Luteal LH receptors also bind hCG resulting
in sustained progesterone production. Administration
of hCG to non-primate females can cause ovulation.
In fact, hCG is used commonly to induce ovulation in
superovulation protocols.
The Placenta Secretes Progesterone
and Estrogens
Progesterone is obligatory for early embry-
onic development because it provides the stimulus for
elevated secretion by the endometrial glands. High
progesterone is also responsible for the so-called "pro-
gesterone block" that inhibits myometrial contractions.
Progesterone increases in the blood of the pregnant
female and peaks at different stages of gestation for
52. different species. The absolute levels of progesterone
also vary significantly among species (See Figure 14-9).
While progesterone is always produced by the corpus
luteum in early pregnancy, the role of the corpus luteum
in maintenance of pregnancy varies among species. In
some species (ewe, mare and woman), the corpus luteum
is not needed for the entire gestational period because
the placenta takes over production of progesterone. For
example, in the ewe the corpus 1uteum is responsible
for initial production of progesterone, but the placenta
assumes responsibility for its production after only 50
days of gestation (See Table 14-1 ). In other species
(sow or rabbit), lutectomy (surgical removal of corpora
lutea) will terminate pregnancy regardless of when this
occurs during gestation. Lutectomy in the cow up to
8 months of gestation will result in abortion. It should
be pointed out that even though the placenta takes over
for the corpus luteum of pregnancy, the corpus luteum
secretes progesterone throughout gestation.
In addition to progesterone, estradiol also is an
important product of the placenta, particularly during
the last part of gestation. In fact, the peak of estradiol
in most species signals the early preparttu·ient period.
The profiles of estradiol during gestation are presented
in the subsequent section on parhrrition.
Cea·tain Placental Hormones
Stimulate Mammaa·y Function of the Dam
and Fetal Growth
The placenta is known to produce a polypep-
tide hom1one known as placental lactogen that is also
called somatomammotropin. Placental lactogens
have been found in rats, mice, sheep, cows and humans.
53. They are believed to be similar to growth hormone, thus
promoting the growth of the fehts. Placental lactogen
also stimulates the mammary gland (lactogenic) of the
dam. The degree to which fetal somatotropic (growth)
versus lactogenic effects occur depends on the species
(See Figure 14-10). For example, in the ewe ovine
placental lactogen (oPL) has a more potent lactogenic
activity than somatotropic activity. A similar condition
exists in humans, but not in the cow. Placentallactogens
have been shtdied most intensely in the ewe. They are
produced and secreted by the binucleate giant cells of
the placenta. The secretory products of the binucleate
cells are transferred into the maternal circulation.
It is hypothesized that the sire may have an
effect on the degree to which the fehts can produce
placental lactogen. Such an effect could cause elevated
concentrations of placental lactogen by the ferns. In-
creased placental lactogen secretion would cause
enhanced stimulation of the maternal manunary gland
and thus promote elevated milk production. This theory
suggests that it might be possible for the sire to influence
fetal placental lactogen and enhance milk production in
the dam. This sire-on-fetus-hypothesis has not been
tested critically, but could hold promise for the genetic
improvement in dairy, beef cattle and goats.
Placental relaxin is secreted in humans, mares,
cats, dogs, pigs, rabbits and monkeys. Its function is to
cause softening and "relaxation" ofthe pelvic ligaments
to facilitate expulsion of the ferns. The stimulus for
relaxin secretion is not known. Relaxin is not present
in the bovine placenta during any stage of gestation. It
is likely (with the exception of the rabbit) that relaxin,
during the time of parrnrition, originates from both the
ovary and the placenta. The role of relaxin is therefore
54. questionable in the cow. Maternal blood relaxin levels
are the basis for a commercial pregnancy diagnostic test
at about 30 days of gestation in the bitch.
Placentation, Gestation and Parturition 305
Figure 14-9. Progesterone Profiles in Various Pregnant Females
so (P = Parturition) -E 40 -..
00
1: 30 -
"C 20
0
0
iil 10
t e 2 3 4 Months of Gestation
"1 - 100 E -..
00
1: - 20
"C
0
..5!
al 10
®
t e 2 4 6 Months of Gestation 8 10 II
14-1. Length and Time of Placental Takeover for Progesterone
Production in
Vanous Spec1es
56. 11.4 mo (none)
2mo (none)
12.3 mo (none)
6-8 mo
50 days
5 mo (none)
11.3 mo (none)
70 days
2 mo (none)
1 mo (none)
3.8 mo (none)
60-70 days
14
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304 Placentation, Gestation and Parturition
The second major gonadotropin of placental
origin is human chorionic gonadotropin (hCG). This
hormone is not only found in the human but in many
57. other primates. Often hCG (and eCG) may simply be
referred to as "CG". It originates from the trophoblas-
tic cells of the chorion and is secreted as soon as the
blastocyst hatches from the zona pellucida. Human
chorionic gonadotropin can be detected in the blood
and urine of the pregnant woman as early as days 8 to
1 0 of gestation. It increases rapidly in the urine of the
pregnant woman, reaching a maximum value at about
2.5 months (See Figure 14-8). Its presence in the urine
constitutes the basis for over-the-counter pregnancy
diagnosis kits.
The primary role of hCG during early preg-
nancy is to provide a luteotropic stimulus for the
ovulatory corpus luteum as it transitions into the CL of
pregnancy. Luteal LH receptors also bind hCG resulting
in sustained progesterone production. Administration
of hCG to non-primate females can cause ovulation.
In fact, hCG is used commonly to induce ovulation in
superovulation protocols.
The Placenta Secretes Progesterone
and Estrogens
Progesterone is obligatory for early embry-
onic development because it provides the stimulus for
elevated secretion by the endometrial glands. High
progesterone is also responsible for the so-called "pro-
gesterone block" that inhibits myometrial contractions.
Progesterone increases in the blood of the pregnant
female and peaks at different stages of gestation for
different species. The absolute levels of progesterone
also vary significantly among species (See Figure 14-9).
While progesterone is always produced by the corpus
luteum in early pregnancy, the role of the corpus luteum
in maintenance of pregnancy varies among species. In
58. some species (ewe, mare and woman), the corpus luteum
is not needed for the entire gestational period because
the placenta takes over production of progesterone. For
example, in the ewe the corpus 1uteum is responsible
for initial production of progesterone, but the placenta
assumes responsibility for its production after only 50
days of gestation (See Table 14-1 ). In other species
(sow or rabbit), lutectomy (surgical removal of corpora
lutea) will terminate pregnancy regardless of when this
occurs during gestation. Lutectomy in the cow up to
8 months of gestation will result in abortion. It should
be pointed out that even though the placenta takes over
for the corpus luteum of pregnancy, the corpus luteum
secretes progesterone throughout gestation.
In addition to progesterone, estradiol also is an
important product of the placenta, particularly during
the last part of gestation. In fact, the peak of estradiol
in most species signals the early preparttu·ient period.
The profiles of estradiol during gestation are presented
in the subsequent section on parhrrition.
Cea·tain Placental Hormones
Stimulate Mammaa·y Function of the Dam
and Fetal Growth
The placenta is known to produce a polypep-
tide hom1one known as placental lactogen that is also
called somatomammotropin. Placental lactogens
have been found in rats, mice, sheep, cows and humans.
They are believed to be similar to growth hormone, thus
promoting the growth of the fehts. Placental lactogen
also stimulates the mammary gland (lactogenic) of the
dam. The degree to which fetal somatotropic (growth)
versus lactogenic effects occur depends on the species
59. (See Figure 14-10). For example, in the ewe ovine
placental lactogen (oPL) has a more potent lactogenic
activity than somatotropic activity. A similar condition
exists in humans, but not in the cow. Placentallactogens
have been shtdied most intensely in the ewe. They are
produced and secreted by the binucleate giant cells of
the placenta. The secretory products of the binucleate
cells are transferred into the maternal circulation.
It is hypothesized that the sire may have an
effect on the degree to which the fehts can produce
placental lactogen. Such an effect could cause elevated
concentrations of placental lactogen by the ferns. In-
creased placental lactogen secretion would cause
enhanced stimulation of the maternal manunary gland
and thus promote elevated milk production. This theory
suggests that it might be possible for the sire to influence
fetal placental lactogen and enhance milk production in
the dam. This sire-on-fetus-hypothesis has not been
tested critically, but could hold promise for the genetic
improvement in dairy, beef cattle and goats.
Placental relaxin is secreted in humans, mares,
cats, dogs, pigs, rabbits and monkeys. Its function is to
cause softening and "relaxation" ofthe pelvic ligaments
to facilitate expulsion of the ferns. The stimulus for
relaxin secretion is not known. Relaxin is not present
in the bovine placenta during any stage of gestation. It
is likely (with the exception of the rabbit) that relaxin,
during the time of parrnrition, originates from both the
ovary and the placenta. The role of relaxin is therefore
questionable in the cow. Maternal blood relaxin levels
are the basis for a commercial pregnancy diagnostic test
at about 30 days of gestation in the bitch.
Placentation, Gestation and Parturition 305
60. Figure 14-9. Progesterone Profiles in Various Pregnant Females
so (P = Parturition) -E 40 -..
00
1: 30 -
"C 20
0
0
iil 10
t e 2 3 4 Months of Gestation
"1 - 100 E -..
00
1: - 20
"C
0
..5!
al 10
®
t e 2 4 6 Months of Gestation 8 10 II
14-1. Length and Time of Placental Takeover for Progesterone
Production in
Vanous Spec1es
SPECIES
Alpaca
Bitch
Camel
62. 6-8 mo
50 days
5 mo (none)
11.3 mo (none)
70 days
2 mo (none)
1 mo (none)
3.8 mo (none)
60-70 days
14
Ve
tB
oo
ks
.ir
306 Placentation, Gestation and Parturition
Figure 14-10. Placental Lactogen in Blood Near
Termination of Gestation
(From Martal in Reproduction in Man and Mammals)
Woman
4000_1
'5:b c - 600 c
CIJ
63. Q
Ewe
0 Somatotropic activity
0 Lactogenic activity
!)0
0 .... u
Ill
...J
iii .... c
CIJ u
Ill
0::
500
400
300
200
100 Cow
0
270 120 ISO 270
Day of Gestation
Parturition is a Complex Cascade of
Physiologic Events
Rat
12
64. The fetus triggers the onset of parh1rition by
initiating a cascade of complex endocrine/biochemical
events. The fetal hypothalamo-pihlitary-adrenal axis is
obligatory for the initiation of parturition. During the
conclusion of gestation, fetal mass approaches the in-
herent space limitations of the uterus. This space limita-
tion has been considered by some to be the stimulus that
causes adrenal corticotropin (ACTH) to be secreted
by the fetal pih1itary. The fetal pituitary then stimulates
secretion of adrenal corticoids from the fetal adrenal
cortex. The elevation of fetal corticoids initiates a
cascade of events that cause dramatic changes in the
endocrine condition of the dam. These endocrine
changes cause two major events to occur: 1) removal of
the myometrial "progesterone block," enabling myome-
trial contractions to begin and 2) increased reproductive
tract secretions, particularly by the cervix.
The three stages of parturition are:
• I: initiation of myometrial
contractions (removal ofprogesterone
block)
• II: expulsion of the fetus
• III: expulsion of the fetal mebranes
Placental lactogen has both
lactogenic actions and soma-
totrophic actions. The lac-
togenic activity of placental
lactogen promotes mammary
function in the dam, while
the somatotropic activity
promotes fetal growth.
65. Removal of the "progesterone block" occurs
because fetal cortisol promotes the synthesis of three
enzymes that convert progesterone to estradiol. The
conversion pathway is illustrated in Figure 14-11.
Progesterone, that is high at the placental interface,
is converted to 17a-hydroxyprogesterone by the en-
zyme !?a-hydroxylase. Fetal cortisol also triggers
the enzyme 17-20 desmolase to convert 17a-hydroxy-
progesterone to androstenedione. Androstenedione is
converted to estrogen by activation of an aromatase
enzyme. This involves aromatization of the A ring of
the steroid and removal of the 19 carbon. The conver-
sion of progesterone to estradiol accounts, at least in
part, for the dramatic drop in progesterone and dramatic
elevation of estradiol. The relationship between pro-
gesterone and estradiol during gestation is presented
in Figure 14-12.
In addition to converting progesterone to es-
h·adiol, fetal corticoids also cause the placenta to syn-
thesize PGF2a.. The synthesis of PGF 2a helps abolish
the "progesterone block." As both estradiol and prosta-
glandin become elevated, the myometrium becomes in-
creasingly more active and begins to display noticeable
contractions. Also, PGF 2a causes the CL of pregnancy
to regress, facilitating the decline in progesterone. The
drop in progesterone in some species is brought about
both by the conversion of progesterone into estradiol
and by the luteolytic process brought about by PGF2a·
Endocrine events associated with parhrrition are sum-
marized in Figures 14-13 and 14-14.
The fetus initiates Stage I of parturition.
Figure 14-11. Conversion of
66. Progesterone to Estradiol as
Parturition Nears
Corticoids from the fetus activate 17 a-hydroxylase,
17-20 desmolase and aromatase that convert
progesterone to estradio l. This conversion
removes the "progesterone block" to myometrial
activity.
17 a Hydroxyprogesterone
Androstenedione
CHJ
I
)
JJ-SD
CH1
I
· ' 1'
0
117: 20 I
l I Aromotase I
o)D'"
OH
. As the pressure inside the uterus continues to
mcrease, the feh1s in the cow, mare and ewe rotates so
the fi·ont feet and head are positioned to the poste-
67. of the dam (See Figure 14-15). Such a rotation is
tmportant to insure a proper delivery. If the fetus fails
to position itself correctly, dystocia (difficult birth)
may occur.
. As the levels of estradiol increase, coupled
With the e l_evation in levels of PGF2a , the contracting
begms to push the fetus toward the cervix, ap-
plymg pressure to the cervix. The endocrine events
that pro?1ote the firs t stage of parturition (dilation of
the cervtx and entry of the feh1s into the cervical canal)
are summarized in Figure 14-14.
Pressure ?n the cervix brought about by in-
myometnal contractions activates pressure-
sensttl_ve neurons located in the cervix that synapse in
the spmal cord and evenhmlly synapse with oxytocin
Ill c
0
'.P
1.': ...,
c
Q) v c
0 u
N w
"'C c
Rl
Placentation, Gestation and Parturition 307
68. Figure 14-12. Estradiol and
Progesterone Profiles During
Gestation in the Mare, Cow,
Woman, Ewe and Sow
(P = Parturition)
Mare
I Woman I
p
I Sow I
t 10 20 30 40 so e Weel<s of Gestation
Ve
tB
oo
ks
.ir
306 Placentation, Gestation and Parturition
Figure 14-10. Placental Lactogen in Blood Near
Termination of Gestation
(From Martal in Reproduction in Man and Mammals)
Woman
4000_1
'5:b c - 600 c
69. CIJ
Q
Ewe
0 Somatotropic activity
0 Lactogenic activity
!)0
0 .... u
Ill
...J
iii .... c
CIJ u
Ill
0::
500
400
300
200
100 Cow
0
270 120 ISO 270
Day of Gestation
Parturition is a Complex Cascade of
Physiologic Events
Rat
12
70. The fetus triggers the onset of parh1rition by
initiating a cascade of complex endocrine/biochemical
events. The fetal hypothalamo-pihlitary-adrenal axis is
obligatory for the initiation of parturition. During the
conclusion of gestation, fetal mass approaches the in-
herent space limitations of the uterus. This space limita-
tion has been considered by some to be the stimulus that
causes adrenal corticotropin (ACTH) to be secreted
by the fetal pih1itary. The fetal pituitary then stimulates
secretion of adrenal corticoids from the fetal adrenal
cortex. The elevation of fetal corticoids initiates a
cascade of events that cause dramatic changes in the
endocrine condition of the dam. These endocrine
changes cause two major events to occur: 1) removal of
the myometrial "progesterone block," enabling myome-
trial contractions to begin and 2) increased reproductive
tract secretions, particularly by the cervix.
The three stages of parturition are:
• I: initiation of myometrial
contractions (removal ofprogesterone
block)
• II: expulsion of the fetus
• III: expulsion of the fetal mebranes
Placental lactogen has both
lactogenic actions and soma-
totrophic actions. The lac-
togenic activity of placental
lactogen promotes mammary
function in the dam, while
the somatotropic activity
71. promotes fetal growth.
Removal of the "progesterone block" occurs
because fetal cortisol promotes the synthesis of three
enzymes that convert progesterone to estradiol. The
conversion pathway is illustrated in Figure 14-11.
Progesterone, that is high at the placental interface,
is converted to 17a-hydroxyprogesterone by the en-
zyme !?a-hydroxylase. Fetal cortisol also triggers
the enzyme 17-20 desmolase to convert 17a-hydroxy-
progesterone to androstenedione. Androstenedione is
converted to estrogen by activation of an aromatase
enzyme. This involves aromatization of the A ring of
the steroid and removal of the 19 carbon. The conver-
sion of progesterone to estradiol accounts, at least in
part, for the dramatic drop in progesterone and dramatic
elevation of estradiol. The relationship between pro-
gesterone and estradiol during gestation is presented
in Figure 14-12.
In addition to converting progesterone to es-
h·adiol, fetal corticoids also cause the placenta to syn-
thesize PGF2a.. The synthesis of PGF 2a helps abolish
the "progesterone block." As both estradiol and prosta-
glandin become elevated, the myometrium becomes in-
creasingly more active and begins to display noticeable
contractions. Also, PGF 2a causes the CL of pregnancy
to regress, facilitating the decline in progesterone. The
drop in progesterone in some species is brought about
both by the conversion of progesterone into estradiol
and by the luteolytic process brought about by PGF2a·
Endocrine events associated with parhrrition are sum-
marized in Figures 14-13 and 14-14.
The fetus initiates Stage I of parturition.
72. Figure 14-11. Conversion of
Progesterone to Estradiol as
Parturition Nears
Corticoids from the fetus activate 17 a-hydroxylase,
17-20 desmolase and aromatase that convert
progesterone to estradio l. This conversion
removes the "progesterone block" to myometrial
activity.
17 a Hydroxyprogesterone
Androstenedione
CHJ
I
)
JJ-SD
CH1
I
· ' 1'
0
117: 20 I
l I Aromotase I
o)D'"
OH
. As the pressure inside the uterus continues to
mcrease, the feh1s in the cow, mare and ewe rotates so
73. the fi·ont feet and head are positioned to the poste-
of the dam (See Figure 14-15). Such a rotation is
tmportant to insure a proper delivery. If the fetus fails
to position itself correctly, dystocia (difficult birth)
may occur.
. As the levels of estradiol increase, coupled
With the e l_evation in levels of PGF2a , the contracting
begms to push the fetus toward the cervix, ap-
plymg pressure to the cervix. The endocrine events
that pro?1ote the firs t stage of parturition (dilation of
the cervtx and entry of the feh1s into the cervical canal)
are summarized in Figure 14-14.
Pressure ?n the cervix brought about by in-
myometnal contractions activates pressure-
sensttl_ve neurons located in the cervix that synapse in
the spmal cord and evenhmlly synapse with oxytocin
Ill c
0
'.P
1.': ...,
c
Q) v c
0 u
N w
"'C c
Rl
Placentation, Gestation and Parturition 307
74. Figure 14-12. Estradiol and
Progesterone Profiles During
Gestation in the Mare, Cow,
Woman, Ewe and Sow
(P = Parturition)
Mare
I Woman I
p
I Sow I
t 10 20 30 40 so e Weel<s of Gestation
Ve
tB
oo
ks
.ir
14
308 Placentation, Gestation and Parturition
producing neurons in the hypothalamus (See Figure
14- I 5). Oxytocin, released into the systemic circula-
tion, acts to facilitate the myomeh·ial contractility
initiated by estradiol and by PGF2u· As the pressure
against the cervix continues to increase, so does the
oxytocin secretion, and thus the force of conh·action of
75. the myometrial smooth muscle begins to peak. When
this occurs, the fetus enters the cervical canal and the
first stage of parturition is complete.
Expulsion of fetus (Stage II) requires
strong myometrial and abdominal
muscle contractions.
Another important hormone involved in suc-
cessful parhrrition is relaxin. Relaxin is a glycopro-
tein that is produced by either the corpus luteum or the
placenta, depending upon the species. The synthesis
of relaxin is stimulated by PGF2a · Relaxin causes a
softening of the connective tissue in the cervix and
promotes elasticity of the pelvic ligaments. Thus,
this hormone prepares the birth canal by loosening
the supportive tissues so that passage of the fehts can
occur with relative ease.
One of the dramatic effects of estradiol
elevation prior to parturition is that it initiates secre-
tory activity of the reproductive tract in general and
particularly the cervix. As estradiol increases, the
cervix and vagina begin to produce mucus. This
mucus washes out the cervical seal of pregnancy
and thoroughly lubricates the cervical canal and the
vagina. Mucus reduces friction and enables the fetus
to exit the reproductive tract with relative ease. As
myometrial contractions continue to increase, the
feet and head of the fehts begin to put pressure on the
fetal membranes. When the pressure reaches a certain
level, the membranes rupture, with subsequent loss of
amniotic and allantoic fluid. This fluid also serves to
lubricate the birth canal. As the fetus enters the birth
canal, it becomes hypoxic (deprived of adequate levels
76. of oxygen). This hypoxia promotes fetal movement
that, in tum, promotes further myometrial contrac-
tion. This positive feedback system creates a set of
conditions where the time of parhtrition is reduced
because an increased strength of contraction follows
fetal movement. In a sense, the fehts is controlling
its exit from the uterus. The uterine contractions are
accompanied by abdominal muscle contractions of the
dam that further aid in expulsion of the fetus.
VI
1:
0
"" "'"' 1:
Ql u
1:
0 u
Ql
1:
0
E
"" 0 :r:
Ql >
1i r:x:
Figure 14-13. Relative
Hormone Profiles in the Cow
During the Periparturient Period
Estrogens
I Prostaglandin
77. -I 0 -B -6 -4 -3 -2 -I 0 I 2 3 4 5
t Parturition
Days
Note that as fetal
cortisol levels rise,
P4 levels fall.
In most species, expulsion of the fetal mem-
branes quickly follows expulsion of the fetus. Expulsion
of the fetal membranes requires that the chorionic villi
become dislodged from the crypts of the matemal side
of the placenta. This release of the chorionic villi is
believed to be brought about by powerful vasoconstric-
tion of arteries in the villi. Vasoconstriction reduces
pressure and thus allows the villi to be released from
the crypts. Obviously in some fonns of placentation,
there must be some maternal vasoconsh·iction. For ex-
ample, in animals that have hemochorial placentation,
matemal blood is adjacent to the fetal placenta. Thus,
if vasoconstriction does not occur on the matemal side,
hemorrhage is likely.
The duration of parhlrition is variable among
species and this variation is summarized in Table 14-2.
Extension beyond what is considered to be the normal
upper-end duration of parturition constitutes a difficult
birth (dystocia). Such prolonged parturition can result
in serious complications to both the fetus and the dam.
Placentation, Gestation and Parturition 309
Figure 14-14. Cascade of Events Prompted by Fetal Cortisol
f t FETAL ACTH
78. f /I Fetal cortisol j
Placental P4 Relaxin enzymes [!iJ I PGF2a I ...,.I
.-----------. t / t ....._____+ -l
I Luteolysis t Secretion by
<;;?tract
Lubrication
t Myometrial
contractions
I+ Pressure
f
t Cervical
stimulation
t Oxytocin
t
Maximum
pressure
Pelvic
ligament
stretching
Ve
tB
oo
ks
.ir
79. 14
308 Placentation, Gestation and Parturition
producing neurons in the hypothalamus (See Figure
14- I 5). Oxytocin, released into the systemic circula-
tion, acts to facilitate the myomeh·ial contractility
initiated by estradiol and by PGF2u· As the pressure
against the cervix continues to increase, so does the
oxytocin secretion, and thus the force of conh·action of
the myometrial smooth muscle begins to peak. When
this occurs, the fetus enters the cervical canal and the
first stage of parturition is complete.
Expulsion of fetus (Stage II) requires
strong myometrial and abdominal
muscle contractions.
Another important hormone involved in suc-
cessful parhrrition is relaxin. Relaxin is a glycopro-
tein that is produced by either the corpus luteum or the
placenta, depending upon the species. The synthesis
of relaxin is stimulated by PGF2a · Relaxin causes a
softening of the connective tissue in the cervix and
promotes elasticity of the pelvic ligaments. Thus,
this hormone prepares the birth canal by loosening
the supportive tissues so that passage of the fehts can
occur with relative ease.
One of the dramatic effects of estradiol
elevation prior to parturition is that it initiates secre-
tory activity of the reproductive tract in general and
particularly the cervix. As estradiol increases, the
cervix and vagina begin to produce mucus. This
80. mucus washes out the cervical seal of pregnancy
and thoroughly lubricates the cervical canal and the
vagina. Mucus reduces friction and enables the fetus
to exit the reproductive tract with relative ease. As
myometrial contractions continue to increase, the
feet and head of the fehts begin to put pressure on the
fetal membranes. When the pressure reaches a certain
level, the membranes rupture, with subsequent loss of
amniotic and allantoic fluid. This fluid also serves to
lubricate the birth canal. As the fetus enters the birth
canal, it becomes hypoxic (deprived of adequate levels
of oxygen). This hypoxia promotes fetal movement
that, in tum, promotes further myometrial contrac-
tion. This positive feedback system creates a set of
conditions where the time of parhtrition is reduced
because an increased strength of contraction follows
fetal movement. In a sense, the fehts is controlling
its exit from the uterus. The uterine contractions are
accompanied by abdominal muscle contractions of the
dam that further aid in expulsion of the fetus.
VI
1:
0
"" "'"' 1:
Ql u
1:
0 u
Ql
1:
0
E
"" 0 :r:
Ql >
81. 1i r:x:
Figure 14-13. Relative
Hormone Profiles in the Cow
During the Periparturient Period
Estrogens
I Prostaglandin
-I 0 -B -6 -4 -3 -2 -I 0 I 2 3 4 5
t Parturition
Days
Note that as fetal
cortisol levels rise,
P4 levels fall.
In most species, expulsion of the fetal mem-
branes quickly follows expulsion of the fetus. Expulsion
of the fetal membranes requires that the chorionic villi
become dislodged from the crypts of the matemal side
of the placenta. This release of the chorionic villi is
believed to be brought about by powerful vasoconstric-
tion of arteries in the villi. Vasoconstriction reduces
pressure and thus allows the villi to be released from
the crypts. Obviously in some fonns of placentation,
there must be some maternal vasoconsh·iction. For ex-
ample, in animals that have hemochorial placentation,
matemal blood is adjacent to the fetal placenta. Thus,
if vasoconstriction does not occur on the matemal side,
hemorrhage is likely.
The duration of parhlrition is variable among
82. species and this variation is summarized in Table 14-2.
Extension beyond what is considered to be the normal
upper-end duration of parturition constitutes a difficult
birth (dystocia). Such prolonged parturition can result
in serious complications to both the fetus and the dam.
Placentation, Gestation and Parturition 309
Figure 14-14. Cascade of Events Prompted by Fetal Cortisol
f t FETAL ACTH
f /I Fetal cortisol j
Placental P4 Relaxin enzymes [!iJ I PGF2a I ...,.I
.-----------. t / t ....._____+ -l
I Luteolysis t Secretion by
<;;?tract
Lubrication
t Myometrial
contractions
I+ Pressure
f
t Cervical
stimulation
t Oxytocin
t
Maximum
pressure
83. Pelvic
ligament
stretching
Ve
tB
oo
ks
.ir
31 0 Placentation, Gestation and Parturition
Figure Pressure on the Cervix Causes Oxytocin Release and
Subsequent Myometrial Contractions
As the fetus moves through the
birth canal , elevated pressure
on the cervix stimulates sensory
neurons. A neural pathway ter-
minates in the paraventricular nu-
cleus (PVN) and causes
to be secreted from the postenor
pituitary lobe. Oxytocin
contraction of the myometnum.
Afferent
neurons
Hypothalamus
Difficulties in parturi tion usually occur in the second
stage (expulsion of the fetus). One cause of dystocia
is excessive size of the fetus. Fetal size is controlled
by both the dam and the sire. In primiparous dams, it
84. is always advisable to breed females to a male of small
body size so that fetal size does not exceed the ability
of the female to give birth successfully.
A second cause of dystocia is failure of proper
fetal rotation. About 5% of all births in cattle are char-
acterized by abnormal positioning of the fetus during
parturition. Such abnormal positioning results in dif-
ficult births and sometimes impossible presentations/
positions that require caesarean section.
A third cause of dystocia is multiple births in
monotocous species. Twins generally cause dystocia.
This is because: 1) both twins may be presented simul-
taneously, 2) the first fetus is positioned abnommlly and
therefore blocks the second or 3) the uterus becomes
fatigued by difficult and sustained contractions. A dis-
cussion of obstetrical procedures used to correct these
problems is beyond the scope of this book, but c .... atfbe
researched by consulting the appropriate references at
the conclusion of this chapter.
Placentation, Gestation and Parturition 311
Expulsion of fetal membranes
(Stage III) requires myometrial
contractions.
Myometrial contractions continue after expul-
sion of the fetus although they are not as strong. These
contractions are responsible for expelling the placenta.
The time required for expulsion of the placenta varies
significantly among species. This variation is presented
in Table 14-2. Retention of the fetal membranes (also
referred to as "retained placenta"), is not uncommon in
85. ruminants, especially dairy cows. This condition will
occur in 5-15% of parturitions in healthy dairy cows.
The underlying cause of retained placenta appears to
be that placental connective tissue is not enzymatically
degraded by cotyledonary proteolytic enzymes. Thus,
fetal cotyledons remain attached to matemal cotyledons.
Retained placenta is rare is mares, sows, bitches and
queens.
Table 14-2. Stages and Duration of Parturition Among Various
Species
Stage I Stage II Stage III
(Mllometrial Contractions/ (Fetal (Fetal Membrane
Cervical Dilation)
Alpaca 2 to 6h 5 to 90 min 45 to 180 min
Bitch 6 to 12h 6h (24h in large litters) most placentas pass with
neonate or within 15 min
of birth
Camel 3 to 48h 5 to 45 min 40 min
Cow 2 to 6h 30 to 60 min 6 to 12h
Ewe 2 to 6h 30 to 120 min 5 to 8h
Llama 2 to 6h 5 to 90 min 45 to 180 min
Mare 1 to 4h 12 to 30 min 1h
Sow 2 to 12h 150 to 180 min 1 to 4h
Queen 4 to 42h 4 kittens/litter, most placentas pass with
86. 30-60 min/kitten neonate
Woman 8+h 2h 1h or less
14
Ve
tB
oo
ks
.ir
31 0 Placentation, Gestation and Parturition
Figure Pressure on the Cervix Causes Oxytocin Release and
Subsequent Myometrial Contractions
As the fetus moves through the
birth canal , elevated pressure
on the cervix stimulates sensory
neurons. A neural pathway ter-
minates in the paraventricular nu-
cleus (PVN) and causes
to be secreted from the postenor
pituitary lobe. Oxytocin
contraction of the myometnum.
Afferent
neurons
Hypothalamus
Difficulties in parturi tion usually occur in the second
stage (expulsion of the fetus). One cause of dystocia
87. is excessive size of the fetus. Fetal size is controlled
by both the dam and the sire. In primiparous dams, it
is always advisable to breed females to a male of small
body size so that fetal size does not exceed the ability
of the female to give birth successfully.
A second cause of dystocia is failure of proper
fetal rotation. About 5% of all births in cattle are char-
acterized by abnormal positioning of the fetus during
parturition. Such abnormal positioning results in dif-
ficult births and sometimes impossible presentations/
positions that require caesarean section.
A third cause of dystocia is multiple births in
monotocous species. Twins generally cause dystocia.
This is because: 1) both twins may be presented simul-
taneously, 2) the first fetus is positioned abnommlly and
therefore blocks the second or 3) the uterus becomes
fatigued by difficult and sustained contractions. A dis-
cussion of obstetrical procedures used to correct these
problems is beyond the scope of this book, but c .... atfbe
researched by consulting the appropriate references at
the conclusion of this chapter.
Placentation, Gestation and Parturition 311
Expulsion of fetal membranes
(Stage III) requires myometrial
contractions.
Myometrial contractions continue after expul-
sion of the fetus although they are not as strong. These
contractions are responsible for expelling the placenta.
The time required for expulsion of the placenta varies
significantly among species. This variation is presented
88. in Table 14-2. Retention of the fetal membranes (also
referred to as "retained placenta"), is not uncommon in
ruminants, especially dairy cows. This condition will
occur in 5-15% of parturitions in healthy dairy cows.
The underlying cause of retained placenta appears to
be that placental connective tissue is not enzymatically
degraded by cotyledonary proteolytic enzymes. Thus,
fetal cotyledons remain attached to matemal cotyledons.
Retained placenta is rare is mares, sows, bitches and
queens.
Table 14-2. Stages and Duration of Parturition Among Various
Species
Stage I Stage II Stage III
(Mllometrial Contractions/ (Fetal (Fetal Membrane
Cervical Dilation)
Alpaca 2 to 6h 5 to 90 min 45 to 180 min
Bitch 6 to 12h 6h (24h in large litters) most placentas pass with
neonate or within 15 min
of birth
Camel 3 to 48h 5 to 45 min 40 min
Cow 2 to 6h 30 to 60 min 6 to 12h
Ewe 2 to 6h 30 to 120 min 5 to 8h
Llama 2 to 6h 5 to 90 min 45 to 180 min
Mare 1 to 4h 12 to 30 min 1h
Sow 2 to 12h 150 to 180 min 1 to 4h
89. Queen 4 to 42h 4 kittens/litter, most placentas pass with
30-60 min/kitten neonate
Woman 8+h 2h 1h or less
14
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14
312 Placentation, Gestation and Parturition
Further
PHENOMENA
for Fertility
The term "caesarean" was derived from the
false notion that Julius Caesar was born by
removing him from his mother through an
incision in the abdominal and uterine wall.
His family name, Caesar was derived from
the belief that Julius' ancestors (centuries
before him) were hom in such a way. The
name Caesar is derived from the Latin word
"caesus" that means "to cut". The name also
fits the way Julius died.
In a number of teleost fishes (fishes with a
more or less ossified skeleton) the female
90. incubates the eggs in her mouth and in some
species the male does the same. The term
"keep your mouth shut" has a special meaning
in this species.
In pipe fishes and sea horses the female lays
her eggs in a brood pouch of the male and he
is responsible for gestation. In fact, several
females may lay eggs in one male's brood
pouch. The brood pouch offers a special
environment for developing offspring and is
under the control of prolactin.
Lampreys (a predatory eel) build nests in
sandy bottomed sh·eams. They assemble rock
walls to slow the water running over the nest.
At spawning, they stir up the sand that sticks
to the eggs. The sand weights the eggs and
prevents them from floating downstream. It
also reduces predation. This is mwtherform
of attachment that enables successful embryo-
genesis.
Infant kangaroos in their mother's pouches
nurse from two nipples, and two babies of
different ages commonly nurse at the same
time. So, the mother kangaroo produces two
kinds of milk- on one side, fully rich for the
younger and 011 the other side, a sort of skim
for the elder.
The most prolific mammal in existence is the
tiny J'Odent known as the multimammate rat.
One female is capable of producing up to 120
offspring a year if conditions are favorable.
This is because she has 24 teats, the most of
91. any female mammal. It is rare that all of them
are used but when they are a multimammate
population explosion catt occur.
The female Egyptian spiny mouse acts as a
midwife to other females. She bites through the
umbilical cord and licks the neonates while the
mother continues to deliver the litter.
The female African elephant has a gestation
period of 1.8 years. The calf weighs about
300 pounds at birth and nurses for about three
years.
Durittg the 19th Century, adultery was so
feared that the chastity belt was invented. Such
belts were devices that were locked around the
genitalia to prevent copulation. It has
been recorded that afaitliful wife locked into a
chastity belt discovered that she was pregnant
some months after her husband had left 011 a
crusade. Her husband had the o11ly key. Her
pregnancy progressed and eventually the vil-
lage blacksmith had to be called in to remove
the chastity belt.
During the Middle Ages, prostitution was
considered to he an honest and essential pro-
fession. This was because prostitution was
considered as a means to prevellt adulte1y,
homosexual behavior and masturbation. The
Church actually condoned prostitution for tlzis
reason.
The Mayans believed in a maize god. Since
92. corn was a nutritional staple for these people,
they revered it and believed that corn was
symbolic of both the male am/female. From a
nutritional perspective they believed that corn
was nurturing like a breast and that
each individual kernel had powerful fertilizing
capabilities like spermatozoa. Once the seeds
were planted in the earth and the mature com
was produced, the cob represented the penis
and the husk represented the vagina. Thus, the
ear of com was also symbolic of copulation.
Kev References
Arthur, G.H., D.E. Noakes, H. Pearson and T.J. Parkin-
son. 1996. Veterinarv Reproduction and Obstetrics.
7th Edition. W.B. Saunders Co. Philadelphia. ISBN
0-7020-1 758-X.
Catchpole, H.R. 1991. "Hormonal mechanisms in
pregnancy and parturition" in Reproduction in Domestic
Animals. 4th Edition. P.T. Cupps, ed., Academic Press,
San Diego. ISBN 0-1 2-196575-9.
Flood, P.F. 199 I. "The development of the conceptus
and its relationship to the uterus" in Reproduction in
Domestic Animals. 4th Edition. P.T. Cupps, ed., Aca-
demic Press, San Diego. ISBN 0-1 2-196575-9.
Fuchs, A.R. and M.J. Fields. 1999. "Parturition, no.!Jhtl-
man mammals" in Encvclopedia o(Reproducilon: Vol.
3 p703-7 I 6. Knobil , E. and J.D . Neill, eds. Academic
Press, San Diego. ISBN 0- 12-227023- 1.
Ginther, OJ . 1992. Reproductive Biology o{the Mare.
2nd Edition. Equiservices, Cross Plains, WI. Library of
93. Congress Catalog No. 9 1-075595.
Johnston, S.D. M.V. Root, Kustritz and P.N.S. Olson.
200 I. Canine and Feline Theriogenologv. W.B. Saun-
ders, Philadelphia. ISBN 0-7216-5607-2.
Morrow, D.A. 1986. Current Therapy in Theriogenol-
2nd Edition. W.B. Saunders Co. Philadelphia.
ISBN 0-7216-6580-2.
Mossman, H.W. 1987. Vertebrate Fetal Membranes.
Rutgers University Press, New Brunsw ick. ISBN
0-8135-1132-1.
Thibault, C., M.C. Levasseur and R.H.F. Hunter.eds.
I 993. Reproduction in Man and Mammals. Ellipses,
Paris. ISBN 2-7298-9354-7.
Placentation, Gestation and Parturition 313
14
Ve
tB
oo
ks
.ir
14
312 Placentation, Gestation and Parturition
Further
94. PHENOMENA
for Fertility
The term "caesarean" was derived from the
false notion that Julius Caesar was born by
removing him from his mother through an
incision in the abdominal and uterine wall.
His family name, Caesar was derived from
the belief that Julius' ancestors (centuries
before him) were hom in such a way. The
name Caesar is derived from the Latin word
"caesus" that means "to cut". The name also
fits the way Julius died.
In a number of teleost fishes (fishes with a
more or less ossified skeleton) the female
incubates the eggs in her mouth and in some
species the male does the same. The term
"keep your mouth shut" has a special meaning
in this species.
In pipe fishes and sea horses the female lays
her eggs in a brood pouch of the male and he
is responsible for gestation. In fact, several
females may lay eggs in one male's brood
pouch. The brood pouch offers a special
environment for developing offspring and is
under the control of prolactin.
Lampreys (a predatory eel) build nests in
sandy bottomed sh·eams. They assemble rock
walls to slow the water running over the nest.
At spawning, they stir up the sand that sticks
to the eggs. The sand weights the eggs and
prevents them from floating downstream. It
also reduces predation. This is mwtherform
of attachment that enables successful embryo-
95. genesis.
Infant kangaroos in their mother's pouches
nurse from two nipples, and two babies of
different ages commonly nurse at the same
time. So, the mother kangaroo produces two
kinds of milk- on one side, fully rich for the
younger and 011 the other side, a sort of skim
for the elder.
The most prolific mammal in existence is the
tiny J'Odent known as the multimammate rat.
One female is capable of producing up to 120
offspring a year if conditions are favorable.
This is because she has 24 teats, the most of
any female mammal. It is rare that all of them
are used but when they are a multimammate
population explosion catt occur.
The female Egyptian spiny mouse acts as a
midwife to other females. She bites through the
umbilical cord and licks the neonates while the
mother continues to deliver the litter.
The female African elephant has a gestation
period of 1.8 years. The calf weighs about
300 pounds at birth and nurses for about three
years.
Durittg the 19th Century, adultery was so
feared that the chastity belt was invented. Such
belts were devices that were locked around the
genitalia to prevent copulation. It has
been recorded that afaitliful wife locked into a
chastity belt discovered that she was pregnant