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Female Reproductive System: Functions
Role of male is to produce and deliver sperm. Role of female is
1. Generate and release fertile ova
2. Maintain fertilized ova throughout development
3. Deliver newborn
4. Nourish newborn
Basic Anatomy
Ovarian Cycle
Beginning at puberty and continuing until menopause, ovaries cycle
between two endocrine states every 28 days or so unless
interrupted by pregnancy.
1. Primary follicles in ovary = primary
oocyte in layer of granulosa cells.
2. Granulosa cells proliferate
-> fluid-filled follicle with oocyte
in granulosa cells
3. Follicular cells secrete estrogens
(mainly estradiol) into circulation
and follicular fluid
Ovarian Cycle (continued)
4. One follicle (usually) grows faster than others, becoming a
mature Graafian follicle.
5. At about 14 days into the cycle, it ruptures. This releases
oocyte and estrogen-rich fluid into body cavity at entrance to
oviducts.
6. This is ovulation; it ends the follicular phase.
Ovarian Cycle (continued)
7. End of follicular phase = beginning of luteal phase.
8. Follicular cells that remain on ovarian surface accumulate
precursors of steroids, which makes them yellow. They’re now
called the corpus luteum (= yellow body)
Ovarian Cycle (continued)
9. Corpus luteum secretes two steroid hormones: lots of
progesterone, not so much estradiol.
10. If the ovum isn’t implanted in the uterus, this phase lasts about
14 days, corpus luteum degenerates and a new follicular phase
begins.
Control of Ovarian Cycle
Hypothalamus releases pulses of GnRH, stimulates LH and FSH
1. Ovulation is triggered by surge in plasma LH levels.
2. LH maintains corpus luteum for about 14 days.
Uterine (Menstrual) Cycle Results from Effects on Uterus
To simplify, pretend that uterus consists only of myometrium
(muscle) and endometrium (lining). Estrogens stimulate growth of
both, induces progesterone receptor formation in endometrium
(follicular phase of ovarian cycle).
Endometrium accumulates electrolytes and water, becomes more
vascular, stores lots of glycogen. Progesterone inhibits myometrial
contractions during luteal phase.
Uterine cycle = proliferative phase (starts around day 7 of ovarian
follicular phase) + menstrual phase (starts around day 28 of
ovarian cycle; during luteal phase).
Day 1 of uterine cycle is defined as first day of menstrual flow.
This happens when corpus luteum degeneration sharply reduces
plasma estrogen and progesterone levels.
Endometrium secretes prostaglandins, which constrict
endometrial vessels. Causes degeneration of endometrium and
stimulates myometrial contractions. Menstrual flow is the
expulsion of dead endometrium. Typical volume = about 100 ml.
After 5 to 7 days, follicular secretion of estrogens ends menstrual
flow and initiates proliferative phase. This ends at ovulation.
Fertilization and Pregnancy
Sperm are deposited in the distal part of the vagina, migrate
through the cervix, uterus, into the oviducts. Fertilization usually
occurs in the distal part of the oviduct, occasionally occurs outside
the oviduct.
Notice how far the sperm travel, and how little must go wrong for
fertilization to happen outside the oviduct. A fertilized egg that
implants outside the uterus is an ectopic pregnancy.
The fertilized ovum is propelled through the oviducts into the
uterus, and if it implants in the uterine wall, a pregnancy begins.
Note how many things can prevent a pregnancy from occurring.
When a fertilized egg implants, it induces formation of placenta,
which supports the embryo/fetus until the end of pregnancy.
Placenta
1. Maternal and fetal blood supplies pass close enough to
exchange materials through capillaries. This provides fetus
with nutrients and oxygen and a route for excretion of wastes.
2. Produces chorionic gonadotropin, which maintains pregnancy
conditions in uterus (maintains corpus luteum, thus preventing
endometrial degeneration).
3. HCG has been the basis of pregnancy tests for about 100 years.
4. Produces estrogens and progesterone during third trimester.
5. After delivery of newborn, placenta detaches and is expelled
(“afterbirth”)
Milk Production
High circulating levels of estrogens during pregnancy stimulates
prolactin secretion.
Prolactin plus placenta’s secretion of chorionic gonadotropin
stimulate mammary glands.
After delivery of newborn, prolactin stimulates milk production,
oxytocin stimulates milk expulsion.
Suckling initiates reflexes that cause hypothalamus to secrete PRH,
which promotes prolactin secretion and maintains milk production.
Also stimulates reflexive release of oxytocin from posterior lobe.
All of this can be conditioned to stimuli other than suckling and can
be inhibited by various kinds of stress.