• If the ovum becomes fertilized, a new sequence
of events called gestation or pregnancy takes
• The fertilized ovum eventually develops into a
• Fertilization of the ovum normally takes place in
the ampulla of one of the fallopian tubes.
• The 23 unpaired chromosomes of the male
pronucleus and the 23 unpaired chromosomes of
the female pronucleus align themselves to re-
form a complete complement of 46
chromosomes (23 pairs) in the fertilized ovum or
WHAT DETERMINES THE SEX OF THE FETUS
THAT IS CREATED?
X chromosome (the female chromosome).
Y chromosome (the male chromosome).
XX combination, a female child will be born.
XY combination, a male child will be born.
EARLY NUTRITION OF THE EMBRYO
ANATOMY AND FUNCTION OF THE PLACENTA:
• The total surface area of all the villi of
the mature placenta is only a few
square meters—many times less than
the area of the pulmonary membrane
in the lungs.
• Nutrients and other substances pass
through this placental membrane
mainly by diffusion in much the same
manner that diffusion occurs through
the alveolar membranes of the lungs
and the capillary membranes
elsewhere in the body.
PLACENTAL PERMEABILITY AND
• The major function of the
placenta is to provide for
diffusion of foodstuffs and
oxygen from the mother’s
blood into the fetus’s blood
and diffusion of excretory
products from the fetus back
into the mother.
• Diffusion of Oxygen Through
the Placental Membrane is:
The same principles for
diffusion of oxygen through
the pulmonary membrane,
which means by simple
• The mean partial pressure of oxygen (PO2) of
the mother’s blood in the placental sinuses is
about 50 mm Hg.
• The mean po2 in the fetal blood after it becomes
oxygenated in the placenta 30 mm Hg.
• The mean pressure gradient for diffusion of
oxygen through the placental membrane is
about 20 mm Hg.
Three reasons why even this low
PO2 is capable of allowing the
fetal blood to transport almost as
much oxygen to the fetal tissues.
1. The hemoglobin of the fetus is
mainly fetal hemoglobin (more
2. The hemoglobin concentration
of fetal blood is about 50
percent greater than that of
3. Double bohr effect: low partial
pressure of carbon dioxide in
fetal blood due to exerted co2
by the fetus will increase the
affinity of o2
HORMONAL FACTORS IN PREGNANCY:
• In pregnancy, the placenta forms especially
1. Human chorionic gonadotropin,
4. Human chorionic
1- Function of Human Chorionic Gonadotropin
• Human chorionic gonadotropin is a glycoprotein having a
molecular weight of about 39,000.
• Function of HCG
• Persistence of the corpus luteum and prevents menstruation.
• Human chorionic gonadotropin stimulates the male fetal testes
to produce testosterone.
• A syncytial trophoblast cells of the placenta.
• Enlargement of the mother’s uterus.
• Enlargement of the mother’s breasts and growth of the breast
ductal structure, enlargement of the mother’s female external
• Relax the pelvic ligaments of the mother.
• Rate of cell reproduction in the early embryo.
• Causes decidual cells to develop in the uterine endometrium. These
cells play an important role in the nutrition of the early embryo.
• Decreases the contractility of the pregnant uterus.
• Contributes to the development of the conceptus even before
• Helps estrogen prepare the mother’s breasts for lactation,
4- HUMAN CHORIONIC
• Often called placental lactogen. It acts like prolactin and growth hormone.
• Enlargement of mammary glands and induces lactation.
• like GH on protein metabolism.
• It reduces the peripheral utilization of glucose in the mother.
• It mobilizes fat from the adipose tissue of the mother
• FETOPLACENTAL UNIT:
• Refers to the interaction between fetus and
placenta in the formation of steroid hormones.
• The interaction between fetus and placenta occurs
because some of the enzymes involved in steroid
synthesis present in fetus are absent in placenta
and those enzymes, which are absent in fetus are
present in placenta.
Other Hormonal Factors in Pregnancy
a) Pituitary Secretion:
• The anterior pituitary gland increases its production
of corticotropin, thyrotropin, and prolactin.
• Pituitary secretion of FSH and LH is almost totally
suppressed as a result of the inhibitory effects of
estrogens and progesterone from the placenta.
b) Increased Corticosteroid Secretion:
• Glucocorticoids is moderately increased.
• Twofold increase in aldosterone secretion (pegnancy
c) Increased Thyroid Gland Secretion:
• Increases its production of thyroxine, and small quantities
of a specific thyroid-stimulating hormone, called human
d) Increased Parathyroid Gland Secretion:
• Enlarge during pregnancy due to insufficiency of Ca in diet.
e) Secretion of “Relaxin” by the Ovaries and Placenta:
• Secreted by the corpus luteum of the ovary and by
• Its secretion is increased by a stimulating effect of human
• Relaxin is a 48–amino acid polypeptide with a molecular
weight of about 9000.
• Cause relaxation of the pelvic ligaments.
Changes in the pregnant woman:
1- Response of the Mother’s Body to Pregnancy:
• The uterus increases from about 50 grams to 1100 grams, and the
breasts approximately double in size.
• The vagina enlarges and the introitus opens more widely.
• The development of edema, acne, and masculine or acromegalic
2- Weight Gain in the Pregnant Woman:
• The average weight gain during pregnancy is about 25 to 35 pounds.
• During pregnancy, a woman often has a greatly increased desire for
3- Metabolism During Pregnancy:
• Secretion of many hormones during pregnancy, including thyroxine,
adrenocortical hormones, and the sex hormones, the basal metabolic
rate of the pregnant woman increases about 15%.
• The extra load she is carrying (fetus), greater amounts of energy than
normal must be expended for muscle activity.
4- Nutrition During Pregnancy:
• Ordinarily, the mother does not absorb sufficient protein,
calcium, phosphates, and iron, Vit D, Vit K from her diet during
the last months of pregnancy to supply these extra needs of the
fetus. To over ride these the mother should take a
5- Changes in the Maternal Circulatory System During Pregnancy:
• Blood flow through the placenta and maternal cardiac output
increase during pregnancy.
• Maternal blood volume increases during pregnancy.
6- Maternal Respiration Increases During Pregnancy:
• the high levels of progesterone and the increased basal
metabolism during pregnancy increase the minute ventilation
7- Maternal Kidney Function During Pregnancy:
• The rate of urine formation by a pregnant woman is usually
slightly increased because of increased fluid intake and
increased load of excretory products.
Amniotic Fluid and Its Formation
• Normally, the volume of amniotic fluid
(the fluid inside the uterus in which the
fetus floats) is between 500 milliliters
and 1 liter.
• A large portion of the fluid is derived
from renal excretion by the fetus.
Preeclampsia and Eclampsia
Preeclamsia toxemia of
1- Increased BP.
Preeclamsia + Convulsion
• Parturition: means birth of the baby.
• Two major categories of effects lead up to the intense
contractions responsible for parturition:
(1) Progressive hormonal changes that cause increased
excitability of the uterine musculature.
(2) Progressive mechanical changes.
• Hormonal Factors That Increase Uterine Contractility:
A. Increased Ratio of Estrogens to Progesterone (estrogens
have a definite tendency to increase the degree of
B. Oxytocin Causes Contraction of the Uterus.
C. Effect of Fetal Hormones on the Uterus (secretion of
oxytosin, fetus’s adrenal glands secrete large quantities
of cortisol ).
• Mechanical Factors That Increase Uterine Contractility:
A. Stretch of the Uterine Musculature (fetal movements,
twins born earlier than single).
B. Stretch or Irritation of the Cervix (obstetricians frequently
induce labor by rupturing the membranes).
• ONSET OF LABOR—A POSITIVE FEEDBACK MECHANISM
FOR ITS INITIATION:
• Braxton Hicks contractions: is the periodic episodes of weak
and slow rhythmical contractions of the uterus. It’s painless.
• Braxton Hicks contractions are triggered by several factors
1. Touching the abdomen
2. Movement of fetus in uterus
3. Physical activity
4. Sexual intercourse
The false labor contractions are believed
to help cervical dilatation.
Remember that for a positive feedback to
continue, each new cycle of the positive
feedback must be stronger than the previous
ABDOMINAL MUSCLE CONTRACTIONS
Once uterine contractions become strong
during labor, pain signals originate both from
the uterus and from the birth canal.
These signals, in addition to causing
elicit neurogenic reflexes in the spinal cord to
the abdominal muscles, causing intense
contractions of these muscles.
STAGES OF PARTURITION:
• First Stage:
• Labor contractions arise from fundus
of uterus and move downwards so that
the head of fetus is pushed against
• Second Stage:
• The fetus is delivered out from uterus
through cervix and vaginal canal. This
stage lasts for about 1 hour.
• Third Stage:
• The placenta is detached from the
decidua and is expelled out from
uterus. It occurs within 10 to 15
minutes after the delivery of the child.
• Involution of the Uterus After
• Endometrial surface autolyzes, causing
a vaginal discharge known as lochia,
which is first bloody and then serous in
nature and continues for a total of
about 10 days
Hormones involved in the
process of parturition
• Maternal Hormones:
• Fetal Hormones
• Placental Hormones
• The breasts begin to develop at
• Estrogens Stimulate Growth of
the Ductal System of the Breasts.
• Growth of the ductal system are
at least four other hormones:
1. Growth hormone.
3. Adrenal glucocorticoids.
• Progesterone Is Required for Full
Development of the Lobule-
PROLACTIN PROMOTES LACTATION
• Prolactin: is secreted by the mother’s anterior pituitary
gland, and its concentration in her blood rises steadily
from the fifth week of pregnancy until birth of the baby.
• The placenta secretes large quantities of human chorionic
somatomammotropin, which probably has lactogenic
• The fluid secreted during the last few days before and the
first few days after parturition is called colostrum; it
contains essentially the same concentrations of proteins
and lactose as milk, but it has almost no fat.
• Growth hormone, cortisol, parathyroid hormone, and
insulin: are necessary to provide the amino acids, fatty
acids, glucose, and calcium required for the formation of
• The Hypothalamus Secretes Prolactin Inhibitory
• The hypothalamus mainly stimulates production of all the
other hormones, but it mainly inhibits prolactin
• The catecholamine dopamine, which is known to be
secreted by the arcuate nuclei of the hypothalamus and
can decrease prolactin secretion as much as 10-fold.
• Suppression of the Female Ovarian Cycles in Nursing
Mothers for Many Months After Delivery:
• Increased prolactin—inhibit secretion of gonadotropin-
releasing hormone by the hypothalamus.
• This inhibition, in turn, suppresses formation of the
pituitary gonadotropic hormones—luteinizing hormone
and follicle-stimulating hormone.
EJECTION (OR “LET-DOWN”) PROCESS
IN MILK SECRETION—FUNCTION OF OXYTOCIN
• Milk is secreted continuously into the alveoli of the
breasts, but it does not flow easily from the alveoli
into the ductal system and, therefore, does not
continually leak from the nipples.
• When the baby suckles, it receives virtually no milk
for the first half minute or so.
• Suckling on one breast causes milk flow not only in
that breast but also in the opposite breast.
• Inhibition of Milk Ejection:
• Many psychogenic factors or even generalized
sympathetic nervous system stimulation throughout
the mother’s body can inhibit oxytocin secretion and
consequently depress milk ejection.
• Antibodies and Other Anti-infectious Agents in
• Multiple types of antibodies and other anti-
infectious agents are secreted in milk along with the
• Several different types of white blood cells are
secreted, including both neutrophils and