The document summarizes the process of oogenesis and the menstrual cycle. It notes that a female is born with around 2 million primordial follicles containing primary oocytes, which decrease to around 400,000 by puberty. During each menstrual cycle, a small number of primary oocytes mature and may be ovulated, while the rest undergo apoptosis. The cycle involves the follicular phase where follicles develop, ovulation of a single oocyte on day 14, and the luteal phase where the corpus luteum forms and secretes progesterone to prepare the uterus for potential implantation. If implantation does not occur, the corpus luteum regresses and menstruation begins.

2.  The germ cells that migrate into the ovaries during early embryonic
development multiply, so that by about 5 months of gestation
(prenatal life) the ovaries contain approximately 6 million to 7 million
oogonia.
 Most of these oogonia die prenatally through a process of apoptosis.
 The production of new oogonia stops at this point and never resumes
again.
 The oogonia begin meiosis toward the end of gestation, at which
time they are called primary oocytes.
 Like spermatogenesis in the prenatal male, oogenesis is arrested at
prophase I of the first meiotic division.
 The primary oocytes are thus still diploid.

3.  Primary oocytes decrease in number throughout a woman’s
life.
 The ovaries of a newborn girl contain about 2 million Primary
oocytes—all she will ever have.
 Each Primary oocyte is contained within its own hollow ball of
single layer of granulosa cells, the Primordial follicle.
 By the time a girl reaches puberty, the number of Primary
oocytes and follicles has been reduced to 400,000.
 Only about 400 of these Primary oocytes will ovulate during
the woman’s reproductive years, and the rest will die by
apoptosis.
 Oogenesis ceases entirely at menopause

5. Definition:
“Monthly rhythmical changes in the secretion of the female
hormones and corresponding physical changes in the ovaries and other
sexual organs”.
Duration: The duration of the cycle averages 28 days. It may be as short as
20 days ar as long as 45 days.
PHASES
 Follicular Phase (Proliferative Phase) (1-14 Day)
• Menstrual Phase (Day 1-5)
• Preovulatory Phase. (Day 6-14)
 Ovulation (Day 14)
 Post Ovulatory Phase (Secretory Phase). (15-28 Day)
• Leuteal Phase (Day 15-26)
• Premenstrual phase. (Last 2 Day)
 Concept of Hypothalamic-Pituitary-ovarian Axis

6.  Primordial Follicle: FSH secretion rises and stimulates 20 to 25 primary
oocytes.
 Primary follicle: The surrounding cells enlarge and become cuboidal; the
follicle is then known as a primary follicle.
 Theca Follciuli : The cuboidal cells multiply and stratify, the follicle as a
whole enlarges, and connective tissue condenses around it to form the
theca folliculi.
• Its outer layer, the theca externa, becomes a fibrous capsule.
• Its inner layer, the theca interna, secretes androgen, which the
granulosa cells convert to estrogen.
 Antral Follicle: the follicular cells begin to secrete an estrogen-rich
follicular fluid, which accumulates in little pools amid the cells. These pools
soon merge and become a fluid-filled cavity, the antrum. The follicle is now
called a secondary (antral) follicle.
 This is the state of development when menstruation ceases around day 5

7.  Overall, the most advanced follicle reduces the FSH supply to other
follicles while at the same time it makes itself more sensitive to the
FSH that remains.
 The less developed, less sensitive follicles undergo atresia, while the
most developed follicle attains a diameter of up to 2.5 cm. This
follicle, called a mature (graafian) follicle, protrudes from the surface
of the ovary like a blister.
 As the follicle matures, the primary oocyte completes meiosis I and
becomes a secondary oocyte.
 This cell begins meiosis II but stops at metaphase II. It is now ready
for ovulation.
 FSH and estrogen also stimulate the maturing follicle to produce LH
receptors, which are important to the next phase of the cycle

8.  The proliferative phase is a time of rebuilding of endometrial tissue lost at the
last menstruation.
 At the end of menstruation, around day 5, the endometrium is about 0.5 mm
thick and consists only of the stratum basalis.
 The stratum functionalis is rebuilt by mitosis from day 6 to day 14.
 The principal processes in this phase are:
• Estrogen from the ovaries stimulates mitosis in the stratum basalis as well as
the prolific regrowth of blood vessels.
• By day 14, the endometrium is about 2 to 3 mm thick.
• Estrogen also stimulates the endometrium to produce progesterone receptors,
thereby preparing it for the progesterone-dominated secretory phase
• Estrogen makes the cervical mucus thin and watery making the cervix easier
for sperms to traverse

10.  The release of an oocyte, typically occurs on day 14, the
midpoint of the average cycle.
 It takes only 2 or 3 minutes.
EVENTS
• In the last day or two of the preovulatory phase, the estrogen level is very
high.
• This estrogen stimulates the anterior pituitary to secrete LH and the
hypothalamus to secrete GnRH. GnRH further induces a surge in FSH and
LH secretion by the pituitary
• The FSH level therefore rises in the last day or two before ovulation, but
the LH level rises even more markedly.

11.  The uterine tube becomes edematous, its fimbriae envelop the ovary and its cilia
create a gentle current in the nearby peritoneal fluid—all in preparation for receiving
the oocyte.
 LH increases blood flow in the follicle.
 More serous fluid filters from the capillaries into the antrum and causes the follicle to
swell rapidly.
 LH also stimulates the theca interna to secrete collagenase, an enzyme that
weakens the ovarian wall over the swelling follicle.
 A nipple like stigma appears on the ovarian surface over the follicle.
 Follicular fluid seeps from the stigma for 1 or 2 minutes, and then the follicle
ruptures.
 The remaining follicular fluid oozes out, carrying the oocyte and the surrounding cells
of the corona radiata
 The oocyte and its attendant cells are normally swept up by the ciliary current and
taken into the uterine tube, although many oocytes fall into the pelvic cavity and die

12. Rise in Basal body temperature
Change in consistency of cervical mucus
Hormonal testing by kits
Twinges of ovarian pain
The most likely time to become pregnant is within 24
hours after the cervical mucus changes consistency and
the basal temperature rises.

13. The postovulatory phase extends from days 15 to 28, from
ovulation to the beginning of menstruation.
This phase of the sexual cycle is the most predictable in
length.
This phase is further subdivided into 2 parts
• Lueteal Phase - first 12
• Premenstrual phase- last 2 days

14.  When the follicle expels the oocyte, it collapses and bleeds into the
antrum.
 As the clotted blood is slowly absorbed, granulosa and theca interna
cells multiply and fill the antrum, and a dense bed of blood capillaries
grows amid them forming Corpus Luteum named for a yellow lipid
that accumulates in the theca interna cells.
 Theca Interna cells are now called lutein cells.
 The anterior pituitary continues to secrete LH, which regulates the
further growth and activity of the corpus luteum. For this reason, LH
is also called luteotropic hormone.
 The lutein cells produce mainly androgen, which the granulosa cells
convert to progesterone and a smaller amount of estrogen.
 Progesterone stimulates developments in the uterus

15.  For a time, the corpus luteum grows and secretes more and more progesterone. But
while progesterone stimulates uterine development, it also seals the fate of the
corpus luteum, because it inhibits the secretion of FSH and LH.
 When the LH level falls critically low, the corpus luteum involutes, or atrophies.
Involution, occurring from days 24 through 26, results in declining progesterone
secretion.
 By day 26 or so, involution is complete and the corpus luteum has become an
inactive scar, the corpus albicans.
 If pregnancy occurs, the corpus luteum remains active for about 3 months.
 Involution of the corpus luteum also ends its negative feedback inhibition of the
hypothalamus.
 The hypothalamus therefore begins to secrete GnRH, the anterior pituitary secretes
FSH in response, and a new crop of follicles begins to develop.

16. The secretory phase is a period of further endometrial
thickening, but this results from secretion and fluid
accumulation rather than mitosis
The principal processes in this phase are:
• Progesterone stimulates the endometrial glands and cells of the stroma
to accumulate glycogen.
• The glands grow wider, longer, and more coiled and secrete a glycogen-
rich fluid into the lumen.
• The lamina propria swells with tissue fluid.
• By the end of the secretory phase, the endometrium is about 5 to 6 mm
thick—a soft, wet, nutritious bed available for embryonic development in
the event of pregnancy.

17.  In the absence of pregnancy, the corpus luteum atrophies and the
progesterone level falls sharply.
 In the absence of progesterone, the spiral arteries of the endometrium
exhibit spasmodic contractions that cause endometrial ischemia
(interrupted blood flow).
 The premenstrual phase is therefore also called the ischemic phase.
 Ischemia leads to tissue necrosis.
 As the endometrial glands, stroma, and blood vessels
 degenerate, pools of blood accumulate in the stratum functionalis.
 Necrotic endometrium falls away from the uterine wall, mixes with blood
in the lumen, and forms the menstrual fluid which discharges out of
cervix and then vagina during menses.(i.e. next 3-5 days)