This chapter is a short review of human reproductive system.

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REPRODUCTIVE SYSTEM
REPRODUCTION:
The process by which plants and animals give rise to offspring and
which fundamentally consists of the segregation of a portion of the parental body by a
sexual or an asexual process and its subsequent growth and differentiation into a new
individual. In animal the process of reproduction is sexual.
Reproduction ensures that life continues and that species do not die
out. Indeed, the ability to reproduce is one of the characteristics of living organisms
Reproductive system:
The reproductive system is a collective of internal and
external organs in both males and female that work together for the purpose of procreating.
The reproductive systems of the male and female have some
basic similarities and some specialized differences. They are the same in that most of the
reproductive organs of both sexes develop from similar embryonic tissue, meaning they
are homologous. Both systems have gonads that produce (sperm and egg or ovum) and sex
organs. And both systems experience maturation of their reproductive organs, which become
functional during puberty as a result of the gonads secreting sex hormones. In short, this is a
known list of sex organs that evolve from the same tissue in a human life
Male reproductive system
The male reproductive anatomy includes internal and external structures. Most of the male
reproductive system is located outside of the man’s abdominal cavity or pelvis. The external
structures of the male reproductive system are the penis, the scrotum and the testicles.
Penis:
The penis is the male organ for sexual intercourse. It has three parts: the root, which
attaches to the wall of the abdomen; the body, or shaft; and the glans, which is the cone-
shaped end of the penis. The glans , which also is called the head of the penis, is covered with

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a loose layer of skin called foreskin.The opening of the urethra, the tube that transports semen
and urine, is at the tip of the glans penis. The penis also contains a number of sensitive nerve
endings.
The body of the penis is cylindrical in shape and consists of three internal chambers.
These chambers are made up of special, sponge-like erectile tissue. This tissue contains
thousands of large spaces that fill with blood when the man is sexually aroused. As the penis
fills with blood, it becomes rigid and erect, which allows for penetration during sexual
intercourse. The skin of the penis is loose and elastic to allow for changes in penis size during
an erection.
Semen, which contains sperm, is expelled through the end of the penis. When the
penis is erect, the flow of urine is blocked from the urethra, allowing only semen to be
ejaculated at orgasm. It is also help in urination.
Figure : Male reproductive system
Scrotum :
The scrotum is the loose pouch-like sac of skin that hangs behind the penis. It
contains the testicles, as well as many nerves and blood vessels. For normal sperm
development, the testes must be at a temperature slightly cooler than the body temperature.
Special muscles in the wall of the scrotum allow it to contract and relax, moving the testicles
closer to the body for warmth and protection or farther away from the body to cool the
temperature.
The scrotum has a protective function and acts as a climate control system for the
testes.

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Testicles (testes):
The testes are oval organs about the size of very large (length:1.5-3
inches) olives that lie in the scrotum, secured at either end by a structure called the spermatic
cord. Most men have two testes.Within the testes are coiled masses of tubes called
seminiferous tubules. These tubules are responsible for producing the sperm cells.
The testes are responsible for making testosterone, the primary male
sex hormone, and for producing sperm.
The internal organs of the male reproductive system, also called accessory organs, include the
following:
Epididymis :
The epididymis is a long (20 feet), coiled tube that rests on the backside of
each testicle.
It functions in the carrying and storage of the sperm cells that are produced
in the testes.
It also is the job of the epididymis to bring the sperm to maturity, since the
sperm that emerge from the testes are immature and incapable of fertilization. During sexual
arousal, contractions force the sperm into the vas deferens.
Vas deferens:
The vas deferens is a long, muscular tube that travels from the epididymis
into the pelvic cavity, to just behind the bladder. The vas deferens transports mature sperm to
the urethra in preparation for ejaculation.
Ejaculatory ducts:
These are formed by the fusion of the vas deferens and the seminal
vesicles. The ejaculatory ducts empty into the urethra.
Urethra:
The urethra is the tube that carries urine from the bladder to outside of the body.
In males, it has the additional function of expelling semen when the man reaches orgasm.
When the penis is erect during sex, the flow of urine is blocked from the urethra, allowing
only semen to be ejaculated at orgasm.

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Seminal vesicles:
The seminal vesicles are sac-like pouches that attach to the vas
deferens near the base of the bladder. The seminal vesicles produce a sugar-rich fluid
(fructose) that provides sperm with a source of energy and helps with the sperms’
motility.The fluid of the seminal vesicles makes up most of the volume of a man’s
ejaculatory fluid, or ejaculate.
Prostate gland:
The prostate gland is a walnut-sized structure that is located below the
urinary bladder in front of the rectum. The prostate gland contributes additional fluid to the
ejaculate. Prostate fluids also help to nourish the sperm. The urethra, which carries the
ejaculate to be expelled during orgasm, runs through the center of the prostate gland.
Bulbourethral glands:
The bulbourethral glands, or Cowper’s glands, are pea-sized
structures located on the sides of the urethra just below the prostate gland. These glands
produce a clear, slippery fluid that empties directly into the urethra. This fluid serves to
lubricate the urethra and to neutralize any acidity that may be present due to residual drops of
urine in the urethra
Testes
The testes (testicles) are the male gonads, that is; they are the primary male reproductive
organs. They fulfil two key functions, the production of gametes (sperm) and the secretion of
hormones, particularly the male hormone testosterone. Other structures in the male
reproductive system, including the male duct system and penis are termed accessory
reproductive organs, because rather than producing gametes, they play an accessory role in
the reproductive cycle, by transporting sperm out of the testes.
Appearance and location:
The testes are firm, mobile organs. A typical man has
two testes approximately 5 cm long, 3 cm wide and 2.5 cm thick. Weighing 10–15 g each, the
testes are suspended outside the body in a fleshy sac called the scrotum. The scrotum attaches
to the body between the base of the penis and anus. The left testis lies slightly lower than the
right.
Structure and function of the testes:
The testes consist of a series of tubules
containing testosterone and sperm-producing cells, which are covered by a multi-layered
tunica. The primary function of the testes is sperm production and the main components of

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the testes which play a role in sperm production are the seminiferous tubules, Sertoli
and Leydig cells.
Tunica:
The multi-layered tunica covers the testes, It facilitate blood supply to the testes and
creates a partition between sperm producing regions of the testes. There are three layers to the
tunica, the tunica vasculosa, tunica albuginea and tunica vaginalis.
Tunica vasculosa
The tunica vasculosa is the inner layer of the tunica and consists of blood
vessels and connective tissue. It is covered by the tunica albuginea and facilitates blood
supply to the testes.
Tunica Albuginea
Tunica albuginea is a dense layer of tissue which encases the testes and
connects to the layers of fibres which surround the epididymis, the first in a series of ducts
which transport sperm out of the testes and into the penis.
The tunica albuginea also extends into the testis, creating partitions between seminiferous
tubules where sperm is produced.
Tunica vaginalis
There are two layers of the tunica vaginalis: the visceral and the parietal.
The visceral layer overlies the tunica albuginea while the parietal layer lines the scrotal
cavity. A thin fluid layer separates the two sections of the tunica vaginalis and reduces
friction between the testes and the scrotum.
Seminiferous tubules:
Seminiferous tubules lie within the testes and are separated
by partitions.They house germ cells (23 chromosomecells which in men replicate to produce
sperm) and are the site of spermatogenesis.Partitions divide the testes into lobules which
contain the seminiferous tubules. Each lobule contains 1–4 seminiferous tubules and each
testis may contain up to 900 of these tubules. The tubules average 50 cm in length and are
tightly coiled within the testis. A typical testis contains up to 800 m of tightly coiled
seminiferous tubules.
Mediastinum:
The mediastinum is a region of tissue which connects to the rete testis.
The mediastinum supports the blood vessels and lymphatic system of the testis and the ducts
within the testis which transport sperm.

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Figure :structure of testes
Straight tubules:
Straight tubules connect seminiferous tubules to the rete testis facilitating
sperm transport. They cross from within partitions which separate seminiferous tubules inside
the testes.
Rete testis:
The seminiferous tubules open into a series of channels called the rete testis.The
rete testis facilitate the transport of sperm from the testes to the sperm transport ducts of the
penis.
Efferent ducts:

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Efferent ducts are located between the rete testes and the epididymis. They
connect the testes to the male ducts and facilitate the transport of sperm from the testes.
Leydig cells (interstitial cells):
In the adult male, the soft connective tissues surrounding the
seminiferous tubules contain interstitial cells of Leydig. These cells are almost non-existent
prior to the commencement of testicular testosterone production at the onset of puberty.
Sertoli cells:
Sertoli cells are also found in the seminiferous tubules; however they do not
play a direct role in sperm or testosterone production.Sertoli cells are thought to influence
the secretion of gonadotrophin releasing hormone (GnRH) from the hypothalamus.Sertoli
cells are linked by tight junctions and form the blood-testes barrier.
Blood-testes barrier:
The blood-testes barrier functions in a similar way to the blood-brain
barrier, separating the testes from the normal circulatory processes of the body. The barrier
prevents blood and other body fluids entering the testes; it allows only secretions from Sertoli
cells to enter the lumen of the seminiferous tubules. In doing so the blood-testes barrier
enables the testes to maintain a fluid balance conducive to sperm development.
Spermatogenesis
The process of male gamete formation including formation of a spermatocyte from
a spermatogonium, meiotic division of the spermatocyte, and transformation of the four
resulting spermatids into spermatozoa.
Spermatogenesis occurs in the wall of the seminiferous tubules, with stem cells at the
periphery of the tube and the spermatozoa at the lumen of the tube. Immediately under the
capsule of the tubule are diploid, undifferentiated cells. These stem cells, called
spermatogonia (singular: spermatagonium), go through mitosis with one offspring going on
to differentiate into a sperm cell, while the other gives rise to the next generation of sperm.

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Spermatogenesis: During spermatogenesis, four sperm result from each primary
spermatocyte, which divides into two haploid secondary spermatocytes; these cells will go
through a second meiotic division to produce four spermatids.
Meiosis begins with a cell called a primary spermatocyte. At the end of the first meiotic
division, a haploid cell is produced called a secondary spermatocyte. This haploid cell must
go through another meiotic cell division. The cell produced at the end of meiosis is called a
spermatid. When it reaches the lumen of the tubule and grows a flagellum (or “tail”), it is
called a sperm cell. Four sperm result from each primary spermatocyte that goes through
meiosis.
Stem cells are deposited during gestation and are present at birth through the beginning of
adolescence, but in an inactive state. During adolescence, gonadotropic hormones from the
anterior pituitary cause the activation of these cells and the production of viable sperm. This
continues into old age.
Disease & disorder of testes
Testicular torsion:
Testicular torsion means that your testicle has rotated in the scrotum. This
can wind up the spermatic cord, cutting off blood supply, nerve function, and sperm transport
to your scrotum

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Orchitis:
Orchitis refers to a swollen or inflamed testicle. Like epididymitis, orchitis often
results from an infection caused by an STI.
Both bacterial and viral infections can cause orchitis. A combination of antibiotics
or antiviral medication, along with nonsteroidal anti-inflammatory drugs or cold packs can
help reduce discomfort and pain. Orchitis usually disappears in 7-10 days.
Hypogonadism:
Hypogonadism happens when one’s body doesn’t make enough
testosterone. It can result from a testicular issue or because your brain doesn’t properly
stimulate hormone production.
One can be born with this condition. It can also happen due to an injury,
infection, or other condition that affects testosterone production.
Hydrocele:
A hydrocele happens when excess fluid builds up in the cavities around one of
your testicles. This is sometimes present at birth, but it can also result from an injury or
inflammation.
Testicular cancer:
Testicular cancer happens when cancerous cells multiply within the
tissue of your testicles. It commonly starts in the tubular testicle structures that help produce
sperm.The cause of testicular cancer isn’t always clear.
Hormonal Control of male Reproduction system
The male reproductive cycles are controlled by the interaction of hormones from the
hypothalamus and anterior pituitary with hormones from reproductive tissues and organs. The
hypothalamus monitors and causes the release of hormones from the pituitary gland.
When the reproductive hormone is required, the hypothalamus sends a gonadotropin-
releasing hormone (GnRH) to the anterior pituitary. This causes the release of follicle
stimulating hormone (FSH) and luteinizing hormone (LH) from the anterior pituitary into
the blood

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At the onset of puberty, the hypothalamus causes the release of FSH and LH into the male
system for the first time. FSH enters the testes and stimulates the Sertoli cells to begin
facilitating spermatogenesis using negative feedback, as illustrated in the figure
LH also enters the testes and stimulates the interstitial cells of Leydig to make and release
testosterone into the testes and the blood.
Testosterone, the hormone responsible for the secondary sexual characteristics that develop
in the male during adolescence, stimulates spermatogenesis. These secondary sex
characteristics include a deepening of the voice, the growth of facial, axillary, and pubic hair,
and the beginnings of the sex drive.
A negative feedback system occurs in the male with rising levels of testosterone acting on the
hypothalamus and anterior pituitary to inhibit the release of GnRH, FSH, and LH. The Sertoli
cells produce the hormone inhibin, which is released into the blood when the sperm count is
too high. This inhibits the release of GnRH and FSH, which will cause spermatogenesis to
slow down. If the sperm count reaches 20 million/ml, the Sertoli cells cease the release of
inhibin, and the sperm count increases.
Female reproductive system
The female reproductive anatomy includes both external and internal structures.
The function of the external female reproductive structures (the genital) is twofold: To enable
sperm to enter the body and to protect the internal genital organs from infectious organisms.

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The main external structures of the female reproductive system include:
Labia majora:
The labia majora (“large lips”) enclose and protect the other external
reproductive organs. During puberty, hair growth occurs and the skin of the labia majora,
which also contain sweat and oil-secreting glands.
Labia minora:
The labia minora (“small lips”) can have a variety of sizes and shapes. They
lie just inside the labia majora, and surround the openings to the vagina (the canal that joins
the lower part of the uterus to the outside of the body) and urethra (the tube that carries urine
from the bladder to the outside of the body). This skin is very delicate and can become easily
irritated and swollen.
Bartholin’s glands:
These glands are located next to the vaginal opening on each side and
produce a fluid (mucus) secretion.
Figure: Female reproductive system

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Clitoris:
The two labia minora meet at the clitoris, a small, sensitive protrusion that is
comparable to the penis in males. The clitoris is covered by a fold of skin, called the prepuce,
which is similar to the foreskin at the end of the penis. Like the penis, the clitoris is very
sensitive to stimulation and can become erect.
The internal reproductive organs include:
Vagina:
The vagina is a canal that joins the cervix (the lower part of uterus) to the outside of
the body. It also is known as the birth canal.
Hymen:
A very thin piece of skin-like tissue called the hymen partly covers the opening of
the vagina. Hymens are often different from person to person. It may be ruptured by sexual
activity or by exercise. It is the traditional symbol of virginity.
Uterus (womb):
The uterus is a hollow, pear-shaped organ that is the home to a developing
fetus. The uterus is divided into two parts: the cervix, which is the lower part that opens into
the vagina, and the main body of the uterus, called the corpus. The corpus can easily expand
to hold a developing baby. A canal through the cervix allows sperm to enter and menstrual
blood to exit.
Ovaries:
The ovaries are small, oval-shaped glands that are located on either side of the
uterus. The ovaries produce eggs and hormones.
Fallopian tubes:
These are narrow tubes that are attached to the upper part of the uterus and
serve as pathways for the ova (egg cells) to travel from the ovaries to the uterus. Fertilization
of an egg by a sperm normally occurs in the fallopian tubes. The fertilized egg then moves to
the uterus, where it implants to the uterine lining.

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Ovary
The female gonads are called the ovaries. The ovaries are paired, oval organs attached to
the posterior surface of the broad ligament of the uterus by the mesovarium.
Structure & function of Ovary:
The ovaries are small, oval-shaped, and grayish in
color, with an uneven surface. The actual size of an ovary depends on a woman’s age and
hormonal status; the ovaries, covered by a modified peritoneum, are approximately 3-5 cm in
length during childbearing years and become much smaller and then atrophic once
menopause occurs. A cross-section of the ovary reveals many cystic structures that vary in
size. These structures represent ovarian follicles at different stages of development and
degeneration
The ovary has 3 components:
 Surface: The surface layer of the ovary is formed by simple cuboidal epithelium, known as
germinal epithelium.
 Cortex: The cortex (outer part) of the ovary is largely comprised of a connective tissue
stroma. It supports thousands of follicles. Each primordial follicle contains an oocyte
surrounded by a single layer of follicular cells.
 Medulla: The medulla (inner part) is composed of supporting stroma and contains a rich
neurovascular network which enters the hilum of ovary from the mesovarium.
Ovarian Ligament:
Several paired ligaments support the ovaries. The ovarian ligament
connects the uterus and ovary. Two peritoneal ligaments attach to the ovary:
 Suspensory ligament of ovary – fold of peritoneum extending from the mesovarium to
the pelvic wall. Contains neurovascular structures.
 Ligament of ovary – extends from the ovary to the fundus of the uterus. It then continues
from the uterus to the connective tissue of the labium majus, as the round ligament of
uterus.
Neurovascular supply:
The main arterial supply to the ovary is via the paired ovarian
arteries. These arise directly from the abdominal aorta (inferior the renal arteries). There is
also a contribution from the uterine arteries.
Venous drainage is achieved by paired ovarian veins. The left ovarian vein drains into the left
renal vein, and the right ovarian vein drains directly into the inferior vena cava.

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The ovaries receive sympathetic and parasympathetic innervation from the ovarian and
uterine (pelvic) plexuses, respectively. The nerves reach the ovaries via the suspensory
ligament of the ovary, to enter the ovary at the hilum.
Figure: ovaries & uterus
Ovarian cycle:
Each month, the ovaries go through a series of stages, depending on stimulation by the
anterior pituitary hormones the follicle stimulating hormone (FSH) and the luteinizing
hormone (LH). A typical female cycle lasts 28 days; however, this can range from 21-35
days.
The ovarian cycle has 2 distinct phases: the follicular phase (days 1-14) and the luteal phase
(days 14-28). The follicular phase is characterized by follicle development and growth, the
goal being that one follicle matures and releases an egg at the time of ovulation, around day
14 of the female cycle. The remaining immature follicles go through stages of degeneration
up until day 28, when the cycle repeats itself. The egg that is released is picked up by the
fimbriae of the uterine tube, and the egg is transported toward the uterus. If fertilization does
not occur, the egg degenerates, and menstruation occurs.
The main functions of the ovaries:
 To produce oocytes (female gametes) in preparation for fertilization
 To produce the sex steroid hormones oestrogen and progesterone, in response to
pituitary gonadotrophins (LH and FSH).
Oogenesis
Oogenesis is the process of development of female gametes or ova or egg that takes place in
ovaries
Oogenesis occurs in the outermost layers of the ovaries. As with sperm production, oogenesis
starts with a germ cell, called an oogonium (plural: oogonia), but this cell undergoes mitosis
to increase in number, eventually resulting in up to one to two million cells in the embryo.

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Oogenesis: The process of oogenesis occurs in the ovary’s outermost layer. A primary oocyte
begins the first meiotic division, but then arrests until later in life when it will finish this
division in a developing follicle. This results in a secondary oocyte, which will complete
meiosis if it is fertilized.
The cell starting meiosis is called a primary oocyte. This cell will begin the first meiotic
division, but be arrested in its progress in the first prophase stage. At the time of birth, all
future eggs are in the prophase stage. At adolescence, anterior pituitary hormones cause the
development of a number of follicles in an ovary. This results in the primary oocyte finishing
the first meiotic division. The cell divides unequally, with most of the cellular material and
organelles going to one cell, called a secondary oocyte, and only one set of chromosomes and
a small amount of cytoplasm going to the other cell. This second cell is called a polar body
and usually dies. A secondary meiotic arrest occurs, this time at the metaphase II stage. At
ovulation, this secondary oocyte will be released and travel toward the uterus through the
oviduct. If the secondary oocyte is fertilized, the cell continues through the meiosis II,
completing meiosis, producing a second polar body and a fertilized egg containing all 46
chromosomes of a human being, half of them coming from the sperm.
Uterus
The uterus is an organ of the female reproductive system. It’s shaped like an upside-down
pear and has thick walls. The uterus’s main function is to house and nourish a fetus until it’s
ready for birth.

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Location:
The uterus sits in the middle of the pelvis, behind the bladder and in front of the
rectum. The actual position of the uterus within the pelvis varies from person to person. Each
position has its own name:
 Anteverted uterus: An anteverted uterus tips slightly forward.
 Retroverted uterus: A retroverted uterus bends slightly backward.
Both of these positions are normal, and the position of the uterus can change throughout a
woman’s life, most frequently after a pregnancy.
Anatomy and function:
Fundus:
The fundus is the upper part of the uterus. It’s broad and curved. The fallopian
tubes attach to the uterus just below the fundus.
Corpus:
The corpus is the main body of the uterus. It’s very muscular and can stretch to
accommodate a developing fetus. During labor, the muscular walls of the corpus contract to
help push the baby through the cervix and vagina.
The corpus is lined by a mucus membrane called the endometrium. This membrane responds
to reproductive hormones by changing its thickness during each menstrual cycle. If an egg is
fertilized, it attaches to the endometrium. If no fertilization occurs, the endometrium sheds its
outer layer of cells, which are released during menstruation.
Isthmus:
The portion of the uterus between the corpus and the cervix is called the isthmus.
This is where the walls of the uterus begin to narrow toward the cervix.
Cervix:
The cervix is the lowest part of the uterus. It’s lined with a smooth mucous
membrane and connects the uterus to the vagina. Glands in the cervical lining usually
produce a thick mucus. However, during ovulation, this becomes thinner to allow sperm to
easily pass into the uterus.
The cervix has three main parts:
 Endocervix: This is the inner part of the cervix that leads to the uterus.
 Cervical canal: The cervical canal links the uterus to the vagina.

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 Exocervix: The exocervix is the outer part of the cervix that protrudes into the vagina.
 During childbirth, the cervix dilates (widens) to allow the baby to pass through the
birth canal.
Hormonal regulation of female reproductive system
The control of reproduction in females is more complex. As with the male, the anterior
pituitary hormones cause the release of the hormones FSH and LH. In addition, estrogens and
progesterone are released from the developing follicles. Estrogen is the reproductive
hormone in females that assists in endometrial regrowth, ovulation, and calcium absorption; it
is also responsible for the secondary sexual characteristics of females. These include breast
development, flaring of the hips, and a shorter period necessary for bone
maturation. Progesterone assists in endometrial re-growth and inhibition of FSH and LH
release.
In females, FSH stimulates development of egg cells, called ova, which develop in structures
called follicles. Follicle cells produce the hormone inhibin, which inhibits FSH production.
LH also plays a role in the development of ova, induction of ovulation, and stimulation of
estradiol and progesterone production by the ovaries. Estradiol and progesterone are steroid
hormones that prepare the body for pregnancy. Estradiol produces secondary sex
characteristics in females, while both estradiol and progesterone regulate the menstrual cycle.
Disease & disorder of Ovaries
Ovarian Cysts:
An ovarian cyst is the enlargement of either ovary beyond 5 cm in size,
which is considered abnormal. Many different types of ovarian cysts exist, each classified as
benign or malignant. The most common benign ovarian cysts in a premenopausal female are
functional cysts, which are typically simple, clear, and nonseptated. The most common
malignant ovarian cysts are epithelial carcinomas. The presence of an ovarian cyst can be
detected on bimanual examination, and the diagnosis can be confirmed by ultrasound
evaluation
Ovarian Torsion:
Ovarian torsion is an ovarian cyst that has grown in size to the point at
which it turns over on itself, twisting the suspensory ligament of the ovary and cutting off
blood supply. The typical presentation of a woman with ovarian torsion is intense, severe,
sudden-onset pain in the right or left lower quadrant. Ultrasound evaluation reveals decreased

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or absent Doppler flow to the ovary on the affected side. The diagnosis of ovarian torsion
warrants emergency surgery to reverse the torsion, hopefully in time to avoid necrosis of the
tissue.
Ovarian Cancer:
Ovarian cancer is detected physically in the same manner as an ovarian
cyst, by bimanual or pelvic examination. Confirmation is then obtained by ultrasound and
further workup as necessary.
Suspicion of an ovarian carcinoma on ultrasound examination includes
characteristics such as complex, multiloculated, septated masses. The tumor marker CA-125
may be tested serologically, and an elevated level may support the diagnosis of ovarian
cancer. This tumor marker is not always helpful, as it can be elevated in noncancerous
conditions such as endometriosis, peritonitis, pregnancy, and liver disease. Ovarian cancer is
an aggressive disease that is often not detected until late stages
Polycystic ovary syndrome:
Polycystic ovary syndrome (PCOS) is a hormonal disorder
common among women of reproductive age. Women with PCOS may have infrequent or
prolonged menstrual periods or excess male hormone (androgen) levels. The ovaries may
develop numerous small collections of fluid (follicles) and fail to regularly release eggs.
The exact cause of PCOS is unknown. Early diagnosis and
treatment along with weight loss may reduce the risk of long-term complications such as type
2 diabetes and heart disease.
Menstrual Cycle
The menstrual cycle is the time from the first day of a woman's period to the day before her
next period The menstrual cycle is the monthly series of changes a woman's body goes
through in preparation for the possibility of pregnancy
The length of the menstrual cycle varies from woman to woman, but the average is to have
periods every 28 days. Regular cycles that are longer or shorter than this, from 21 to 40 days,
are normal.
"Girls can start their periods anywhere from age 10 upwards, but the average is around 12
years," says Belfield. "The average age for the menopause (when periods stop) in this country
is 50 to 55."
Between the ages of 12 and 52, a woman will have around 480 periods, or fewer if she has
any pregnancies.

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To understand the menstrual cycle, it helps to know about the reproductive organs inside a
woman's body. These are:
a. 2 ovaries – where eggs are stored, developed and released
b. the womb (uterus) – where a fertilised egg implants and a baby develops
c. the fallopian tubes – two thin tubes that connect the ovaries to the womb
d. the cervix – the entrance to the womb from the vagina
The menstrual cycle is controlled by hormones. In each cycle, rising levels of the hormone
oestrogen cause the ovary to develop and release an egg (ovulation). The womb lining also
starts to thicken.
General overview of the menstrual cycle: The menstrual cycle includes several phases. The exact
timing of the phases of the cycle is a little bit different for every woman and can change over time.
Cycle days (approximate) Events of the menstrual cycle
Days 1-5 The first day of menstrual bleeding is considered
Day 1 of the cycle.
Your period can last anywhere from 3 to 8 days,
but 5 days is average.
Bleeding is usually heaviest on the first 2 days
Days 6-14 Once the bleeding stops, the uterine lining (also
called the endometrium) begins to prepare for the
possibility of a pregnancy.
The uterine lining becomes thicker and enriched in
blood and nutrients
Day 14-25 Somewhere around day 14, an egg is released
from one of the ovaries and begins its journey
down the fallopian tubes to the uterus.
If sperm are present in the fallopian tube at this
time, fertilization can occur.
In this case the fertilized egg will travel to the
uterus and attempt to implant in the uterine wall
Days 25-28 If the egg was not fertilized or implantation does
not occur, hormonal changes signal the uterus to
prepare to shed its lining, and the egg breaks down
and is shed along with lining.
The cycle begins again on Day 1
menstrual bleeding

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Comprehensive explanation of the menstrual cycle:
The menstrual cycle has three phases:
1. Follicular Phase (Days 1-14):
This phase of the menstrual cycle occurs from
approximately day 1-14. Day 1 is the first day of bright red bleeding, and the end of this
phase is marked by ovulation. While menstrual bleeding does happen in the early part of this
phase, the ovaries are simultaneously preparing to ovulate again. The pituitary gland (located
at the base of the brain) releases a hormone called FSH – follicle stimulating hormone. This

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hormone causes several ‘follicles’ to rise on the surface of the ovary. These fluid filled
“bumps” each contain an egg. Eventually, one of these follicle becomes dominant and within
it develops a single mature egg; the other follicles shrink back. If more than one follicle
reaches maturity, this can lead to twins or more. The maturing follicle produces the hormone
estrogen, which increases over the follicular phase and peaks in the day or two prior to
ovulation. The lining of the uterus (endometrium) becomes thicker and more enriched with
blood in the second part of this phase (after menstruation is over), in response to increasing
levels of estrogen. High levels of estrogen stimulate the production of gonadotropin-releasing
hormone (GnRH), which in turn stimulates the pituitary gland to secrete luteinizing hormone
(LH). On about day 12, surges in LH and FSH cause the egg to be released from the follicle.
The surge in LH also causes a brief surge in testosterone, which increases sex drive, right at
the most fertile time of the cycle.
2. Ovulatory Phase (Day 14):
The release of the mature egg happens on about day
14 as a result of a surge in LH and FSH over the previous day. After release, the egg enters
the fallopian tube where fertilization may take place, if sperm are present. If the egg is not
fertilized, it disintegrates after about 24 hours. Once the egg is released, the follicle seals over
and this is called the corpus luteum.

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3. Luteal Phase (Days 14-28):
After the release of the egg, levels of FSH and LH)
decrease. The corpus luteum produces progesterone. If fertilization has occurred, the corpus
luteum continues to produce progesterone which prevents the endometrial lining from being
shed. If fertilization has not occurred, the corpus luteum disintegrates, which causes
progesterone levels to drop and signals the endometrial lining to begin shedding.
Oestrous cycle
The estrous cycle or oestrus cycle is the recurring physiological changes that are induced
by reproductive hormones in most mammalian therian females. Estrous cycles start after
sexual maturity in females and are interrupted by anestrous phases or by pregnancies.
Typically, estrous cycles continue until death. Some animals may display bloody vaginal
discharge, often mistaken for menstruation.
Phases of the estrous cycle
The following are five periods used to describe the estrous cycle, as developed by Walter
Heape.
 Proestrus:
One or several follicles of the ovary are starting to grow. Their number is
specific for the species. Typically this phase can last as little as one day or as long as 3
weeks, depending on the species. Under the influence of estrogen, the lining in the
uterus (endometrium) starts to develop.
 Estrus:
Estrus refers to the phase when the female is sexually receptive.Under
regulation by gonadotropic hormones, ovarian follicles are maturing and estrogen
secretions exert their biggest influence. The animal exhibits a sexually receptive
behavior, a situation that may be signaled by visible physiologic changes.Ovulation
may occur spontaneously in some species,while in others it is induced by copulation. If
there is no copulation in an induced ovulator, estrus may continue for many days,
followed by interestrus, and the estrus phase starts again until copulation and ovulation
occur.
 Metestrus:
During this phase, the signs of estrogen stimulation subside and the corpus
luteum starts to form. The uterine lining begins to secrete small amounts
of progesterone. This phase typically is brief and may last 1 to 5 days. In some animals
bleeding may be noted due to declining estrogen levels.
 Diestrus:
Diestrus is characterized by the activity of the corpus luteum that produces
progesterone. In the absence of pregnancy, the diestrus phase terminates with the

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regression of the corpus luteum. The lining in the uterus is not shed, but will be
reorganized for the next cycle.
 Anestrus:
Anestrus refers to the phase when the sexual cycle rests. This is typically a
seasonal event and controlled by light exposure through the pineal gland that releases
melatonin. Melatonin is thought to act by regulating hypothalamic pulse activity of
GnRH. Anestrus is induced by time of year, pregnancy, lactation, significant illness,
and possibly age.
Difference between oestrous cycle & menstrual cycle:
Mammals share the
same reproductive system, including the regulatory hypothalamic system that
produces gonadotropin-releasing hormone in pulses, the pituitary gland that secretes follicle-
stimulating hormone and luteinizing hormone, and the ovary itself that releases sex
hormones including estrogensand progesterone.
However, species vary
significantly in the detailed functioning. One difference is that animals that have estrous
cycles resorb the endometrium if conception does not occur during that cycle. Animals that
have menstrual cycles shed the endometrium through menstruation instead. Another
difference is sexual activity. In species with estrous cycles, females are generally only
sexually active during the estrus phase of their cycle. This is also referred to as being "in
heat". In contrast, females of species with menstrual cycles can be sexually active at any time
in their cycle, even when they are not about to ovulate.
Humans have menstrual cycles rather than estrous cycles.They, unlike most other species,
have concealed ovulation, a lack of obvious external signs to signal estral receptivity
at ovulation. There are, however, subtle signs to which human males may favorably respond,
including changes in a woman's scent and facial appearance. Some research also suggests that
women tend to have more sexual thoughts and are more prone to sexual activity right before
ovulation.
PLACENTA
A temporary organ that joins the mother and fetus, transferring oxygen and nutrients from
the mother to the fetus and permitting the release of carbon dioxide and waste products from
the fetus. The placenta is roughly disk-shaped, and at full term it measures about 7 inches in
diameter and slightly less than 2 inches thick. The upper surface of the placenta is smooth,
and the under surface is rough. The placenta is rich in blood vessels. The placenta is expelled
with the fetal membranes during the birth process; together, these structures form the after
birth.

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SRTUCTURE:
Placental mammals, such as humans, have a chorioallantoic placenta that
forms from the chorion and allantois. In humans, the placenta averages 22 cm (9 inch) in
length and 2–2.5 cm (0.8–1 inch) in thickness, with the center being the thickest, and the
edges being the thinnest. It typically weighs approximately 500 grams. It has a dark reddish-
blue or crimson color. It connects to the fetus by an umbilical cord of approximately 55–
60 cm (22–24 inch) in length, which contains two umbilical arteries and one umbilical
vein. The umbilical cord inserts into the chorionic plate. Vessels branch out over the surface
of the placenta and further divide to form a network covered by a thin layer of cells. This
results in the formation of villous tree structures. On the maternal side, these villous tree
structures are grouped into lobules called cotyledons. In humans, the placenta usually has a
disc shape, but size varies vastly between different mammalian species
Figure of placenta
Functions of Placenta:
1. Nutrition:
Food materials pass from the mother’s blood into the foetal blood through the
placenta.

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2. Digestion:
The trophoblast ol the placenta digest protein before passing them into foetal
blood.
3. Respiration:
Through the placenta oxygen passes from the maternal blood to the foetal
blood, and carbon dioxide passes from foetal blood to maternal blood.
4. Excretion:
Nitrogenous wastes such as urea pass from foetal blood into maternal blood
through placenta and are filtered out by the kidneys of the mother.
5. Storage:
The placenta stores glycogen, fat etc. for the foetus before liver is formed.
6. Barrier:
Placenta functions as an efficient barrier (defensive wall) and allows useful: aerials
to pass into the Social blood. Harmful substances such as nicotine from cigarette and
addictive drugs such as heroin can pass through placenta. Therefore, pregnant women should
avoid cigarette and drugs. Viruses and bacteria can pass through placenta.
7. Endocrine function:
Placenta functions as an endocrine gland it secretes hormones such
as oestrogen, progesterone and human chorionic gonadotropin (HCG).
DIAGNOSIS OF PREGNANCY
The diagnosis of pregnancy requires a multifaceted approach using 3 main diagnostic tools:
1.history and physical examination
2. hormonal assays
3.ultrasound (US).
 The diagnosis of pregnancy traditionally has been made from history and physical
examination. Important aspects of the menstrual history must be obtained.

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 Several hormones can be measured and monitored to aid in the diagnosis of
pregnancy. The most commonly used assay tests are for the beta subunit of hCG.
Other hormones that have been utilized include progesterone (P) and early pregnancy
factor (EPF).
 With the advent of transvaginal ultrasound (TVUS), the diagnosis of pregnancy can
be made even earlier than is capable with transabdominal scans. US has long been
used in uncomplicated pregnancies for dating and as a screening exam for fetal
anomalies.
Different types of results in different trimester are given below:
THE FIRST TRIMESTER (0-12 WEEKS)
Symptoms:
 Amenorrhoea: sudden cessation of a previously regular menstruation is the most common
symptom denoting pregnancy. However, pregnancy may occur during lactational
amenorrhoea. On the other hand, bleeding may occur early in pregnancy as in threatened
abortion. Slight bleeding may occur also at the expected time of menstruation in the first 12
weeks of pregnancy but never afterwards due to separation of parts of the decidua vera.
 Morning sickness: nausea with or without vomiting commences in the morning. It
usually appears about 6 weeks after onset of the last menstrual period and usually
disappears 6-12 weeks later.
 Frequency of micturition: due to congestion and pressure on the bladder and
disappear after the first trimester to reappear again near the end of pregnancy when
the foetal head descends into the maternal pelvis.
 Breast symptoms: as enlargement, sensation of fullness, tingling and tenderness.
 Appetite changes and sleepiness.
Signs:
 Breast signs:
o Increase in size and vascularity.
o Increase pigmentation of the nipple and primary areola.
o Appearance of the secondary areola.
o Montgomery’s follicles.
o Expression of colostrum.

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o Breast signs are diagnostic only in primigravidae. In multigravidae, it may be
due to the previous pregnancies.
 Uterine signs:
o The uterus becomes enlarged, globular and soft.
o Palmer's sign: uterine contractions felt during bimanual examination.
o Hegar's sign: during bimanual examination, the two fingers in the anterior
fornix can be approximated to fingers of the abdominal hand behind the uterus
due to softening of the lower part of the uterus and its emptiness. This sign can
be elicited between 6-10weeks but not after as the growing conception will fill
the whole uterine cavity.
 Cervix: soft, hypertrophied and violet.
 Vagina: violet, moist, warm with increased acidity.
Investigations:
Pregnancy tests:
These depend on presence of human chorionic gonadotrophin (hCG) in maternal serum and
urine.
 Urine pregnancy tests:
 Agglutination Test: Latex particles, or sheep erythrocyte (tube) coated with anti-hCG.
 Agglutination Inhibition Tests
 Dip stick
 Rapid and simple tests based on enzyme-labelled monoclonal antibodies assay can
detect low level of hCG in urine
 Causes of false positive results:
 Proteinuria.
 Haematuria.
 At time of ovulation (cross reaction with LH).
 HCG injection for infertility treatment within the previous 30 days.
 Thyrotoxicosis (high TSH).
 Premature menopause (high LH & FSH).
 Early days after delivery or abortion.
 Trophoblastic diseases.
 hCG secreting tumours.

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 Causes of false negative results:
 Missed abortion.
 Ectopic pregnancy.
 Too early pregnancy.
 Urine stored too long in room temperature.
 Interfering medications.
 Serum pregnancy tests:
o Radioimmunoassay of b -subunit of hCG.
o Radio receptor assay.
 Enzyme- linked immunosorbent assay (ELISA).
o can be used for urine and serum.
 Sensitivity of pregnancy tests:
Lowest hCG detectable
(mIU/ml)
Minimum Day post
ovulatory
I- Urine
a- Slide 500-2500 17-26
b- Tube 75-1000 14-22
II- Serum
a-
Radioimmunoassay
300-500 9
b- Radiorecepter 100-200 9
III- ELISA 50 7-10
 Thepregnancy test becomes negative about:
 one week after labour,
 2 weeks after abortion, and
 4 weeks after evacuation of vesicular mole.
 Uses of pregnancy test:
 Diagnosis of pregnancy.
 Diagnosis of foetal death.
 Diagnosis of ectopic pregnancy.
 Diagnosis and follow up of gestational trophoblastic diseases.

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Ultrasonography:
Gestational sac can be detected after 4-5 weeks of amenorrhoea. Foetal heart pulsation can be
detected as early as 7 weeks.
THE SECOND TRIMESTER (13-28 WEEKS)
Symptoms:
 Amenorrhoea.
 Morning sickness and urinary symptoms decrease.
 Quickening: The first sensation of the foetal movement by the mother, occurs at 18-20
weeks in primigravida and at 16-18 weeks in multiparas.
 Abdominal enlargement.
Signs
 Breast signs: become more manifested.
 Skin signs: Cloasma, linea nigra and striae gravidarum appear.
 Uterine signs:
o The uterus is felt abdominally.
o Braxton Hick's contractions: intermittent painless contractions can be felt by
abdominal examination.
 Foetal signs:
o Internal ballottement: can be elicited at 16 weeks by a push to the foetal parts
with the two fingers through the anterior fornix.
o External ballottement: can be elicited at 20 weeks by a push to the foetal parts
with one hand abdominally and the other hand receiving the impulse.
o Palpation of foetal parts and movement: by the obstetrician at 20 weeks.
o Foetal heart sound: can be auscultated at 20-24 weeks by the Pinard's
stethoscope.
o Umbilical (funic) souffle: A murmur with the same rate of FHS due to rush of
blood in the umbilical arteries. It is occasionally detected when a loop of the
cord lies below the stethoscope.
Investigations in doubtful cases:
 Pregnancy tests.
 Ultrasonography.
 X-ray: It shows the foetal skeleton starting from the 16th week of pregnancy. It has
been replaced by ultrasonography due to the following hazards:
o Teratogenic effects particularly before 10 weeks.
o Chromosomal changes in the foetal gonads leading to genetic disorders in the
following generations.
o Subsequent leukaemia in childhood.

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THE THIRD TRIMESTER (29-40 WEEKS)
All signs of pregnancy become more evident. Pregnancy tests are positive, sonar and X-ray
are diagnostic.
Sure Signs of Pregnancy:
 Palpation of foetal parts.
 Palpation of foetal movements.
 Auscultation of foetal heart sounds.
 The occasional auscultation of the umbilical (funic) souffle.
 Detection of foetal skeleton by X-ray.
 Ultrasonographic detection of foetal parts, movements and /or heart movements.
Differential Diagnosis of Pregnancy:
 Early pregnancy:
o Causes of amenorrhoea.
o Causes of symmetrically enlarged uterus:
 Myoma.
 Adenomyosis.
 Pyometra.
 Haematometra.
 Metropathia haemorrhagica.
o Pelvi-abdominal swellings:
 Ovarian swellings.
 Tubal swellings.
 Pelvic haematocele.
 Full bladder.
 Late pregnancy:
o Myomas.
o Ovarian neoplasm.
o Ascitis.
o Pseudocyesis.
o Other causes of pelvi-abdominal mass.
DIFFERENT TYPES OF REPRODUCTIVE HORMONES
A type of hormone involved in fertility and sexuality. Reproductive hormones are usually
made in the ovaries (in females) and testes (in males). Female reproductive hormones include
estrogen and progesterone. They help develop and maintain female sex characteristics and

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play an important role in the menstrual cycle, fertility, and pregnancy. Male reproductive
hormones, such as testosterone, help develop and maintain male sex characteristics and help
make sperm in the testes. Some reproductive hormones may also be made in the laboratory
and used to treat certain medical conditions.
Gonadotropin Releasing Hormone (GnRH)
GnRH is a neuropeptide (a decapeptide) that is produced in the hypothalamic
surge and tonic centres. In the male and the female, the target tissue is the anterior pituitary
gland, specifically Gonadotroph cells. In males and females, secretion of GnRH results in
the release of Follicle Stimulating Hormone (FSH) and Leutinising Hormone (LH) from
the anterior pituitary gland.GnRH-producing neurons are stimulated into production in
response to spontaneous rhythms and by sensory impulses from sensory inputs derived from
the external environment. Alterations in the internal conditions of the body can also result in
altered GnRH production. For example in some species such as the sheep, there is seasonal
sexual activity and the cerebral cortex, hypothalamus, pituitary and testes interact to regulate
functions further along the signalling chain
Luteinising Hormone (LH)
LH is a type of glycoprotein that is produced in the anterior pituitary via gonadotroph cells
and serves to regulate the function of the gonads. In males LH stimulates the production and
secretion of testosterone from the testes via leydig cells. In females LH stimulates the
production of oestrogens and progesterone from the ovary via theca interna cells and luteal
cells. Concentrations of LH increase during ovulation and with the formation of the corpora
lutea with progesterone secretion. The secretion of LH is regulated via the secretion of GnRH
Follicle Stimulating Hormone (FSH)
FSH is a type of glycoprotein that is produced in the anterior pituitary via gonadotroph
cells. FSH secretion is regulated by GnRH from the hypothalamus. The target tissue of FSH
in males are the sertoli cells within the testes and in the female the granulosa cells of the
ovary. FSH stimulates the maturation of germ cells within the testes and ovaries. In the
female it also stimulates follicular development and oestradiol synthesis.
In the male FSH also stimulates the secretion of inhibin which has a negative feedback
directly to the anterior pituitary. Although GnRH is released in a pulsatile fashion and the
other gonadotropic hormone LH is therefore also pulsatile, FSH concentrations do not
fluctuate as much as that of LH. This is because of the added regulatory feedback mechanism
of inhibin within the regulatory pathways for FSH secretion.
The reference range for FSH in adult males is 2 – 12 IU/L and for LH is 2 – 9 IU/L.

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For female:
Phase FSH (IU/L) LH (IU/L)
Early follicular 3 - 10 2 - 8
Mid-cycle peak 4 - 25 10 - 75
Post-menopausal > 20 > 15
Pregnancy < 1 2 - 9
Prolactin (PRL)
Prolactin is a protein that is produced from by the anterior pituitary via lactotroph cells.
This hormone exerts a stimulatory effect on milk synthesis within the mammary glands. It
has also been shown to have some degree of gonadal function in some domestic species and
rodents. In birds increased concentrations of prolactin have been linked with brooding
behaviours and the associated metabolic changes that birds undergo during brooding.
Prolactin secretion is regulated by the hypothalamus which produces several neurohormones
that affect prolactin concentrations. The most important within this is dopamine (or prolactin
inhibitory hormone, PRL-IH) which exerts a totally dominant inhibitory action on prolactin
synthesis. The hypothalamic regulation of prolactin secretion is via signals from the central
nervous system. Prolactin synthesis is increased when the mother is suckling via a reflex
stimulation of the teats. This stimulation reflex reduces the secretion of dopamine and
increases the hormone prolactin releasing hormone(PRL-RH). Once prolactin binds to it's
target receptors within the mammary gland cells, it activates an intracellular tyrosine kinase.
When this occurs in the developing animal this binding can also cause the differentiation of
mammary epithelial cells during pregnancy. The half-life of prolactin is approximately
20mins
Reference ranges are assay-specific so it is recommended to consult the local laboratory for
their reference range. An example of a reference range for prolactin is 50 – 650 mU/L for
adult females and 50 – 450 mU/L for adult males.

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Oxytocin (OT)
OT is a neuropeptide (a octapeptide) which is synthesised in the hypothalamus and stored in
the posterior pituitary. OT is primarily involved in upregulating the activity of smooth muscle
cells in the uterus and the smooth muscles surrounding the alveoli ducts of the mammary
glands. At parturition, OT causes strong contractions from the myometrium. OT is also
essential for 'milk let-down' in most domestic species.OT binds to receptors in the membrane
of target cells which activates phospholipase C. OT facilitates the generation of the driving
pressure behind pushing the milk towards the large excretory ducts and the teats.
Progesterone (P4)
Progesterone is a steroid hormone that along with oestrogens is based on a cholesterol
molecule produced by the corpus luteum and the placenta using cholesterol as the base
molecule. Progesterone is produced by the corpus luteum as well as by the feto-placental unit
and in the zona reticularis of the adrenal cortex (to a lesser extent). More detailed information
regarding corpus luteum formation and regression please use the links. Progesterone prepares
the uterus for reception of fertilized oocytes and is transported via the blood bound to plasma
proteins. Progesterone also prepares the mammary tissues for milk production as well as
inhibiting female reproductive behaviours associated with oestrous.
Effects on reproductive organs:
 Vagina: slight mucous secretion, paleness, exfoliation
 Cervix: closure, formation of the mucous plug
 Uterus: stimulates uterine gland secretions, sensitization of the endometrium to
oxytocin, decreases uterine motility, immunosuppression, inhibition of PGF2a and
PGE2
 Fallopian tube: increased secretion, decreased motility
 Mammary gland: stimulates lobulo-alveolar development
There are no indications, other than fertility investigation in females (in some circumstances),
which requires progesterone measurement in a general practice setting.
Reference range:
Detecting ovulation – measured on day 20 – 23 of a normal 28 day cycle:
The reference range for progesterone in adult males is < 1 nmol/L.
0 – 6 nmol/L ovulation unlikely
7 – 25 nmol/L ovulation possible
> 25 nmol/L ovulation likely

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Testosterone (T)
The male sex hormone is called testosterone and this hormone is required
for spermatogenesis. Testosterone is a steroid hormone that is produced in the leydig cells
within the testes. A relatively high concentration of testosterone is maintained within the
testicular tissue and testosterone is circulated around the body by diffusion of the hormone
from the spermatic cord into the testicular veins and arteries. The primary action of
testosterone is anabolic growth, spermatogenesis promotion and promotion of secretion from
the accessory sex glands. Male sex hormones are regulated by negative feedback systems that
operate at various levels within the male sex hormone system. The starting point for the
production of testosterone (and therefore the production of spermatozoa)is the hypothalamus.
The hypothalamus contains neuroendocrine cells that are capable of secreting a substance
called Gonadotropin-releasing hormone or GnRH. GnRH stimulates basophilic cells in the
adenohypophysis, via the "portal system" to secrete two intermediate hormones within the
male sex hormone cycle; Luteinizing hormone (LH) and Follicle-Stimulating
Hormone (FSH).
The reference range for total testosterone in adult males differs between laboratories. An
approximate range is 8 – 35 nmol/L. If a single early morning testosterone level is clearly
within the reference range (e.g. >15 nmol/L) then no further testing is required
Testosterone reference ranges for females are also assay-specific. An example of an adult
female reference range for total testosterone is 0.5 – 2.5 nmol/L
Inhibin
Inhibin is a type of glycoprotein that is synthesised within the granulosa cells of ovarian
follicles in females and in sertoli cells located in the seminiferous tubules within the testes in
the male. In both males and females the target organ for inhibin is the adenohypophysis,
specifically the gonadotroph cells (basophilic cells). In the male inhibin production is
stimulated via androgens. Inhibin inhibits FSH secretion, which together with decreased
concentrations of LH and testosterone results in decreased spermatogenesis and therefore
decreased sperm output and quality. In females some studies have suggested that inhibin may
also be produced by the placenta. In females inhibin inhibits FSH secretion. It does however
not have any effect on the secretion of LH. When inhibin is secreted, a relatively higher
concentration of LH is secreted from the anterior pituitary gland than FSH. Therefore during
follicle development, the increased LH concentration causes cessation of the recruitment of
further follicles under the effect of FSH. The hormonal changes resulting from the production
of inhibin cause some of the previously recruited follicles to undergo atresia.
Inhibin in the female can also be diminished by GnRH and enhanced by insulin-like growth
factor-1 (IGF-1)

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Human Chorionic Gonadotrophin (hCG)
hCG is a form of glycoprotein that is synthesised within the trophoblast cells of a blastocyst.
hCG is particularly important in primate reproduction where it has a similar effect to LH in
stimulating the continued production of progesterone and oestrogens. This represents part of
the system involved in foetal-maternal communication and pregnancy recognition. Primate
blastocysts therefore produce hCG in relatively high concentrations during the first 3 months
of pregnancy. hCG has also been suggested to play a role in defence of the embryo from the
maternal immune system during the initial stages of pregnancy. In males hCG increases the
growth of the foetal testes. As hCG is only produced by embryonic cells, the presence of this
hormone within maternal blood can be used for pregnancy confirmation
There is a wide range of variability of hCG levels during early pregnancy. The rate of
increase, i.e. doubling time, gives more useful information than the actual levels. Most urine
tests turn positive with hCG levels > 20 – 25 IU/L. Serum hCG < 5 IU/L is considered
negative for pregnancy.
Excessively high hCG levels, e.g. > 100 000 IU/L may be suggestive of gestational
trophoblastic disease, e.g. molar pregnancy
Relaxin
Relaxin is produced mainly by the corpus luteum in most species and in the placenta(main
contributor in the equine) and ovaries throughout pregnancy. During pregnancy relaxin
prevents the initiation of uterine contractions, together with progesterone. Relaxin
accumulates troughtout pregnancy and is released in lare amounts a few days before partus.
Its target organs are the cervix, vagina, pubic symphesis and related structures. Relaxin is
responsible for the softening and relaxation of connective tissues in the cervix, muscles and
ligaments in the pelvis prior to parturition. Estradiol priming is required for this. This
relaxation of tissues via relaxin is performed in conjunction with prostaglandin.
Prostaglandin F2α
Prostaglanin is a C2O fatty acid and is produced within the uterine endometrium and vesicular
glands. Estradiol stimulates prostaglandin synthesis while progesterone inhibits it. The target
tissue in the female is the corpus luteum, uterine myometrium and ovulatory follicles. In the
female PGF2α cause luteolysis and can also cause the induction of tone and contractions
within the uterus. It plays an important role in partuition in ruminants.
If a pregnancy is to remain viable then luteolysis needs to be avoided and this is achieved
where concentrations of PGF2α remain below a threshold level allowing the corpus luteum to
continue to secrete progesterone and thus maintain pregnancy. There are two main factors
involved in the regulation of uterine secretions of PGF2α; oxytocin secretions from the corpus
luteum and molecules secreted by the developing embryo that facilitate the maternal
recognition of pregnancy.

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Prostaglandin (PGE2)
PGE2 is another form of prostaglandin that is produced by the ovary, uterus and embryonic
membranes. This form of prostaglandin also has other important roles including vasodilation,
smooth muscle relaxation, and inhibition of the release of noradrenaline from sympathetic
nerve terminals. In females it's target tissue is the cervix (it is a potent cervical
dilator), corpus luteum and the oviduct where it helps induce ovulation and the secretion of
progesterone from the corpus luteum. PGE2 also plays an important role during labour where
it aids the softening of the cervix in animals with a soft-type cervix(equine and human) and
aids stimulation of uterine contractions. It can thus be used to prepare the tract for parturition
Activin
Activin is a glycoprotein that is produced within granulosa cells in females and sertoli cells in
the male. Activin is thought to play an almost directly opposite role to that of inhibin and is
involved in many physiological functions including stimulation of FSH synthesis and other
roles including cell proliferation, cell differentiation, apoptosis and homeostasis.
The target tissue for activin in the male is the epididymis where it enhances spermatogenesis
via increased FSH secretion. Activin also enhances the effect of LH on the testes.
In the female activin has an effect on the anterior pituitary gland, specifically on gonadotroph
cells, resulting in increased FSH secretion. The increased concentrations of activin results in
increased FSH binding on the female follicle and FSH-induced aromatisation (increased
synthesis of oestrogens). Activin also enhances the action of LH in the ovary.
A further non-reproductive role of activin is it's role in skin lesions where it is thought to
stimulate keratinocytes
Estradiol (E2)
Estradiol (E2) is a steroid hormone and is part of the oestrogens group of hormones and is the
principle oestrogen in females. Estrone and estriol are chemically similar to estradiol but are
found in lower concentrations and have a lower estrogenic activity. Production of oestrogens
occurs in the ovary via granulosa cells, the placenta and the Zona reticularis of the adrenal
cortex. In males in it is produced in sertoli cells found in the testes. Estradiol is synthesised
from cholestrol. Oestrogens have a number of functions related to reproduction and other
areas of physiology. In relation to the reproductive role of oestrogens, they stimulate
follicular growth and maturation, induce the female to begin displaying oestrous behaviour to
facilitate mating, prepare the external genitalia for copulation and create favourable
conditions for the development of fertilised egg cells. Oestrogens also contribute to the

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growth and development of mammary tissue and prepare the uterus for parturition.
Effects on reproductive organs:
 Vagina: slight mucous secretion, hyperaemia, oedema Cervix: relaxation, liquification
of mucous plug (causing the bull string)
 Uterus: stimulates uterine gland development, sensitization of the endometrium to
oxytocin,immune activation (local), leucocyte infiltration, secretion of PGF2a and
PGE2
 Fallopian tube: increased motility and cilia activity
 Mammary gland: stimulates mammary duct development
 Corpus luteum: Luteolytic (bovine and ovine) but luteotrophic (equine and porcine)
The adult female reference range for oestradiol is:
Phase Oestradiol (pmol/L)
Early follicular < 300
Ovulatory surge < 500 - 3000
Luteal surge 100 - 1400
Post-menopausal < 200
The adult male reference range for oestradiol is assay dependent, so it is recommended to
consult the local laboratory. An example of an adult male reference range for oestradiol is 0 –
200 pmol/L.
References:
1. https://my.clevelandclinic.org/health/articles/9117-male-reproductive-system
2. https://www.myvmc.com/anatomy/anatomy-of-the-testes/
3. https://opentextbc.ca/biology/chapter/24-4-hormonal-control-of-human-
reproduction
4. https://emedicine.medscape.com/article/1949171-overview
5. https://www.healthline.com/human-body-maps/uterus
6. https://www.yourperiod.ca/normal-periods/menstrual-cycle-basics/
7. https://en.wikipedia.org/wiki/Estrous_cycle
8. https://www.gfmer.ch/Obstetrics_simplified/Diagnosis_of_pregnancy.htm
9. https://en.wikivet.net/Reproductive_Hormones_Overview_-
_Anatomy_%26_Physiology
10. https://bpac.org.nz/BT/2013/February/02_hormones.aspx