Many structures in the female reproductive system are homologous to
the male structures already studied (homologous means similar in structure,
position, and origin but not necessarily function). The ovaries are
homologous to the testes, labia majora are homologous to the scrotum,
the clitoris is homologous to the penis, the bulb of vestibule is homologous
to the corpora spongiosum & bulb of penis, the paraurethral glands
are homologous to the prostate, and the greater vestibular glands are
homologous to the bulbourethral glands.
Females go through puberty as do males, but there is a distinct nutritional
component to the onset of puberty in females. Nutrition is more important
for puberty in girls than in boys (although puberty is delayed when
either is malnourished) since approximately 140,000 calories are required
to support 9 months of fetal growth and 3 months of lactation. The onset
of puberty correlated with body weight & fat (about 16 kg fat needed
for menarche). Young women athletes, who typically have less adipose,
often experience menarche around age 16. After menarche, extreme weight
loss or rigorous athletic training may lead to absence of menstruation
or amenorrhea. In Europe & U.S., better nutritional standards over
past 200 years have caused average age of menarche to drop from 17 to
13 years; poorly nourished women (New Guinea, !Kung tribeswomen) may
not experience until age 18 and may not conceive until age 25. In females,
growth spurt accompanied by a "fat spurt"; 11 kg fat gained
in female-specific areas: neck, posterior arm, mammary, abdominal, prepubic,
thigh, flank, and calf; some of these deposits completely mask her underlying
The synthesis of the female gametes, the ova, is called oogenesis. Around
the 3rd month (of fetal development, oogonia develop to larger cells
known as primary oocytes; each primary oocytes enter prophase of Meiosis
I where they halt development until puberty. Each primary oocyte is
surrounded by epithelial (follicular) cells known as the primordial
follicle; these nourish the oocyte. Around 7 million potential oocytes
in fetal ovary at 5 months; this is reduced to 1 million at birth and
few hundred thousand at puberty. Each month after menarche, several
primordial follicles respond to FSH causing them to become primary follicles.
In these primary follicles, the primary oocytes complete the first round
of cell division (Meiosis I). This cell divides into to produce a second
oocyte and a 1st polar body which contains little more than discarded
material. The secondary oocyte contains most cytoplasm and remains in
secondary follicle (now several layers of cuboidal and columnar [granulosa]
cells). This cell proceeds to metaphase of Meiosis II and then stops.
At ovulation, the secondary oocyte, the first polar body, and some supporting
cells are discharged and these enter the Fallopian tube.
If fertilization is to occur, the secondary oocyte must encounter sperm
within the first 12-24 hours after ovulation. If fertilized, the secondary
oocyte completes Meiosis II which produces a second polar body and an
ovum (mature egg). The 1st polar body may also divide and all polar
bodies then disintegrate in last part of fallopian tube or uterus (unfertilized
secondary oocytes) disintegrate in the same area).
Thus there are a number of differences in gametogenesis between males
2) FALLOPIAN TUBES (OVIDUCTS)
The oviducts stretch about 4" from the ovary to the uterus. The
first region of the oviduct, the infundibulum, has fingerlike projections
called fimbriae attach to ovary which catch the secondary oocyte at
ovulation and transport it into the tube. Cilia line the cells of the
oviduct and the current they create (plus the muscle contractions from
the wall of the oviduct) help to propel the secondary oocyte). When
infected, as in pelvic inflammatory disease; sterility can result. About
80% of cases are caused by gonorrhea although normal bacteria may also
The uterus is divided into three regions: the fundus, body, and cervix.
Secretory cells of the cervix secrete 20-60 ml of cervical fluid/day.
Near the time of ovulation, this fluid becomes more alkaline and less
viscous, allowing sperm to pass and the mucus protects sperm from vaginal
acid. At other times of the menstrual cycle, it's more viscous, forming
a cervical plug. It produces nourishment for the bacteria which inhabit
the vagina. These bacteria produce acids which protect the vagina infection.
The uterus can be divided into three 3 layers:
a) outer perimetrium
b) myometrium-The myometrium contains 3 layers of smooth muscle. The
contractions of these muscles expell the child in childbirth under the
influence of oxytocin. Their contractions also help to propel sperm
and to discharge the menstrual flow.
c) endometrium--highly vascularized with blood vessels
--The endometrium is organized into 2 layers: the deeper stratum basalis
gives rise to stratum functionalis which is shed every month during
A pap smear examines cells from cervix and vagina in search of the
abnormal morphology of cancer cells.
The vagina attaches to the cervix at the fornix. Initially covered with
a mucus membrane called the hymen that incompletely covers the vaginal
orifice. An imperforate hymen may require surgery to permit menstrual
flow. The hymen is usually torn & destroyed during 1st intercourse
although rough activities such as horse back riding may also cause it
5) VULVA (EXTERNAL GENETALIA)
a) mons pubis: rise above urogenital openings containing adipose &
pubic hair; cushions pelvis during intercourse
b) labia majora: contain a number of glands: apocrine, sebaceous &
c) labia minora: contains sebaceous glands
d) clitoris: erectile tissue that enlarges with tactile stimulation;
plays role in sexual excitement
e) vestibule: cleft between the labia majora which contains openings
to urethra & vagina. Paraurethral glands on either side of the urethra
and greater vestibular glands secrete mucus that functions as lubrication
An episiotomy: surgical cut enlarging the vaginal opening; prevents
a jagged, uncontrolled tear in childbirth. There is some debate today
as to whether this procedure is preformed more often than is necessary.
6) MAMMARY GLANDS
We are mammals-a group of animals which actually get their name from
the mammary glands which produce the nutrition for the young. Mammary
glands are modified sweat glands attached to chest muscles by connective
tissue. Each breast contains 15-20 lobules of mammary glands separated
by adipose. The amount of adipose controls the size and has no relation
to milk production. Milk is transported through secondary tubules to
mammary ducts to lactiferous sinuses (near nipple which may store milk)
to lactiferous ducts to nipple. Between 15 and 20 lactiferous ducts
open onto each nipple. The areola is the pigmented area around these
ducts. Cells of an active mammary gland are depicted below.
Mammary glands develop in females with estrogen & progesterone which
govern duct development, fat deposition, & areolar development.
The hormones prolactin, estrogen, & progesterone are needed for
milk manufacture; oxytocin is needed for ejection (made in response
Hormone changes over the menstrual cycle lead to changes in the breast
and this may cause it to become inflamed. If an inflamed lobule is walled
off with scar tissue, it forms a benign cyst.
One out of 9 American women will have breast cancer at some point in
their lives and it represents the #1 cause of death women aged 35-45.
The following image is of malignant cells in a breast cancer.
The highest rates are known in Causcasian women while Asian & American
Indian rates lowest. Risk factors for breast cancer include: a family
history (mutations in the genes BRCA1, BRCA2, and p53 can be passed
throughout a family), pregnancy after the age of 30, early menarche,
late menopause. Mammography is the best method to detect lumps under
1 cm; most lumps are found in self exams. Once a tumor is larger than
2 cm, the chances of survival decrease rapidly. If no lymph nodes are
involved, chances of 5 year survival 82%; if 4 or more nodes are involved,
21%. Breast cancer may be treated with hormones, chemotherapy, radiation,
lumpectomy, or masectomy. About 35% breast cancers are estrogen dependent
and its continual growth needs estrogen. The removal of ovaries often
causes remission; if cancer recurs, adrenals can be removed (they also
Estrogens at puberty cause the development & maintenance of female
reproductive structures (especially the endometrial lining), female
specific fat distribution, and increased protein production. There really
is no such thing as "male or female hormones" since both genders
have both estrogen and testosterone: estrogens are made from testosterone
and testosterone may be converted to estrogen intracellularly as its
active form. Unlike androgens, estrogens have few effects outside primary
& secondary sexual tissues. Estrogens increase the number of cell
divisions in certain tissues (such as breasts, endometrium); and thus
promotes cancer (the more times a cell divides, the more likely a mistake
is made). Breast, uterine and cervical cancer are more likely in women
with earlier menarche and late menopause since the more cycles, the
more cell divisions and the greater the chance that mutations occur.
Menstrual cycles may last 24-35 days; the average is 28. The menstrual
cycle can be divided into a menstrual phase, preovulatory phase, ovulation,
and a postovulatory phase.
a) Menstrual Phase, days 1-5 (may last 1-7 days)
During the menstrual phase, 50-150 ml blood, tissue fluid, mucus, and
endometrial cells are lost. The low levels of estrogen & progesterone
prior to this causes spiral arteries which feed the functional layer
of the endometrium to constrict and the cells denied of blood supply
begin to die and are sloughed off. The hormone GnRH from the hypothalamus
causes the release of FSH from the pituitary which affects the ovary.
Between 20-25 primordial follicles develop into primary follicles; each
of which begins to make low levels of estrogen. At this rate, few if
any follicles remain 40 years later. In the following image, an ovary
full of primordial follicles is depicted. The corpus albicans is a structure
from the previous menstrual cycle which is in the process of degenerating
as a new cycle begins.
Primordial follicles are depicted below.
A primary follicle is depicted below.
Amenorrhea, or the lack of menstruation may be caused by drastic weight
decrease, severe depression or grief; or even stress (marriage, 1st
affair). Local hormones called prostaglandins may cause cramps; prostaglandin
inhibitors can relieve them.
b) Preovulatory Phase, days 6-13
In the preovulatory phase, about 20 secondary follicles exist which
begin to develop a folicular liquid inside. By day 6, one follicle has
outgrown the others; usually it alone will reach maturity and the others
degenerate. Estrogen secretion inhibits the secretion of FSH which in
turn inhibits the production of more estrogen; only the largest makes
enough estrogen to support itself. The secondary follicle becomes a
vesicular follicle, a blisterlike bulge on the ovarian surface (if more
than one forms, fraternal twins are possible). The endometrial lining
increases from 4 to 6 mm in width under the influence of estrogen.
c) Ovulation; day 14
At ovulation, the vesicular follicle ruptures (15 mm in diameter), releasing
the secondary oocyte. About 20 days have passed since the primordial
follicle began its development toward the end of the previous menstrual
cycle. The first round of metaphase is completed and the cell proceeds
to metaphase the second meiotic division.
Estrogen reaches its peak secretion at which point it initiates positive
feedback on the secretion of GnRH and LH. The surge in the secretion
of LH causes ovulation. After ovulation, the vesicular follicle in the
ovary collapses; a clot is formed and reabsorbed; LH influences the
change of the remaining follicular cells into the corpus luteum that
will secrete estrogen and progesterone. The corpus luteum is an endocrine
organ which survives 12 days in the absence of fertilization.
How can a woman know when she is ovulating? There is no certain way
of knowing for most women, but a few factors can be considered. At ovulation,
the basal temperature increases .4 to .6 degrees Celsius; the following
24 hours represents the optimum time to become pregnant. At ovulation,
estrogen increases the secretion of cervical mucus which becomes clear
and stretchy (forceps can stretch it 12-15 cm). A softening of the cervix
& possible ovarian pain may accompany ovulation.
d) Post-Ovulation; days 15-28
The corpus luteum secretes progesterone that causes the endometrial
glands to grow & coil as they begin to make glycogen. A corpus luteum
is depicted below.
The corpus luteum also increases the vascularization of the endometrium
which thickens it and builds up tissue fluid.
The progesterone & estrogen secreted by corpus luteum decreases
the secretion of GnRH & LH that cause it to degenerate to the corpus
As estrogen & progesterone levels decrease, GnRH & FSH levels
will increase again and another menstrual cycle begins. If fertilization
and implantation occur, human chorionic gonadotropin (hCG) from the
chorion maintains the corpus luteum; the palcenta later secretes estrogen
There are around 8 deaths/100,000 pregnancies; before age 35, any form
of contraception is safer than pregnancy. Over age 35, the risks of
using the pill increase, especially among smokers; smokers should look
for another form of birth control.
a) sterilization: tubal ligation, vasectomy
b) prevent gamete release: birth control pills, norplant, male GnRH
pills soon to be approved
c) prevent gamete fusion: condoms, diaphragm, cervical cap, coitus interruptus,
rhythm method, spermicidal ointments, creams
d) prevent implantation: IUD, morning after pill