FEMALE

REPRODUCTIVE SYSTEM


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 muscle.
Cat
cat
Monkey
monkey
1) OVARIES
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 and females:


--In males, spermatogonia replenish themselves and therefore men will be able to make gametes for as long as they live. In females. all oogonia have begun oogenesis before birth and therefore there is a maximum number of gametes a woman can produce in her lifetime.
--Oogenesis produces 1 functional gamete while spermatogenesis produces 4 for every cell that begins meiosis.
--In males, spermatogenesis begins and ends in a short period of time while in females it begins before birth and ends only at conception. A woman who has never conceived has technically never made a female gamete (since secondary oocytes, rather than ova are released at ovulation).

Monkey
oviducts
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 cause this.

human model

3) UTERUS
The uterus is divided into three regions: the fundus, body, and cervix.

modeluterus

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 menstruation.

A pap smear examines cells from cervix and vagina in search of the abnormal morphology of cancer cells.

4) VAGINA
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 to break.

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 & sudoriferous glands
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 in intercourse.
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.
pelvis
6) MAMMARY GLANDS

breast
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
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 to suckling).
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.

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 produce estrogens)


MENSTRUAL CYCLE
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)
menstrual phase
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.
ovary
Primordial follicles are depicted below.
follicles
A primary follicle is depicted below.
primary follicle

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
ovary
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.

ovary

follicle

follicle

preovulatory

c) Ovulation; day 14
ovulation
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.

corpus luteum

corpus luteum
The corpus luteum also increases the vascularization of the endometrium which thickens it and builds up tissue fluid.
posovulatory
The progesterone & estrogen secreted by corpus luteum decreases the secretion of GnRH & LH that cause it to degenerate to the corpus albicans.

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 and progesterone.

PREGNANCY

BIRTH CONTROL
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