The Female Reproductive System

Female Reproductive System

  • Function: produce offspring, gametes, and hormones.
  • Organs: ovaries, uterine tubes, uterus, vagina, vulva, breasts, mammary glands.

Female Genitalia

  • Internal: ovaries, uterine tubes, uterus, vagina.
  • External: clitoris, labia minora, labia majora, associated glands and erectile tissues (perineum).
  • Primary sex organs: ovaries.
  • Secondary sex organs: other internal and external genitalia.

Ovaries

  • Female gonads that produce egg cells (ova) and sex hormones.
  • Almond-shaped, located in the ovarian fossa of the posterior pelvic wall.
  • Tunica albuginea capsule.
  • Outer cortex: germ cell development.
  • Inner medulla: major arteries and veins.
  • Follicle: fluid-filled sac where each egg develops.
  • Ovulation: follicle bursts, releasing the egg.

Fallopian Tubes

  • Uterine tubes (oviducts): ~10 cm long, from ovary to uterus.
  • Regions:
    • Infundibulum: flared distal end with fimbriae.
    • Ampulla: middle and longest part.
    • Isthmus: narrowed portion near the uterus.
  • Wall is muscular, lined with ciliated and secretory cells; cilia beat toward the uterus.

Uterus

  • Thick, muscular chamber opening into the roof of the vagina.
  • Tilts forward over the urinary bladder.
  • Harbors fetus, provides nutrition, and expels fetus.
  • Regions:
    • Fundus: broad superior curvature.
    • Body: middle portion.
    • Cervix: cylindrical inferior end.
  • Cervical canal connects the lumen of the uterus to the vagina; mucus prevents microorganism spread.

Uterine Wall

  • Perimetrium: outermost, thin serosa.
  • Myometrium: middle muscular layer, produces labor contractions.
  • Endometrium: inner mucosa, functional and basal layers. Functional layer shed during menstruation, basal layer regenerates.

Vagina

  • Distensible muscular tube, ~8-10 cm long.
  • Allows for menstrual fluid discharge, receipt of semen, and birth.
  • Wall: adventitia, muscularis, mucosa.
  • Vaginal rugae: transverse friction ridges.
  • Hymen: mucosal folds across the vaginal opening.
  • Stratified squamous epithelium after puberty; bacteria ferment glycogen to lactic acid, creating an acidic pH.

External Genitalia (Vulva/Pudendum)

  • Mons pubis: mound of fat over pubic symphysis.
  • Labia majora: thick folds of skin and adipose tissue.
  • Labia minora: thin, hairless folds medial to labia majora; form prepuce over clitoris.
  • Clitoris: erectile, sensory organ.
  • Vestibular bulbs: erectile tissue deep to labia majora.
  • Greater & lesser vestibular glands, paraurethral glands: provide lubrication.

Breasts & Mammary Glands

  • Breasts enlarge at puberty.
  • Mammary glands develop during pregnancy and atrophy after nursing ceases.
  • Structure: body, axillary tail, areola (with sensory nerve fibers and areolar glands).
  • During pregnancy, mammary gland exhibits 15-20 lobes around the nipple; lactiferous ducts drain each lobe.

Puberty

  • Begins at age 8-10, triggered by rising levels of gonadotropin-releasing hormone (GnRH).
  • FSH stimulates ovarian follicles to secrete estrogen, progesterone, inhibin, and androgens.
  • Thelarche: onset of breast development.
  • Pubarche: appearance of pubic and axillary hair.
  • Menarche: first menstrual period.
  • Estradiol stimulates vaginal metaplasia, growth of sex organs, increased height and widening of pelvis, fat deposition, and thickening of skin.
  • Progesterone prepares the uterus for possible pregnancy.
  • Hormones are secreted cyclically.

Climacteric & Menopause

  • Climacteric: midlife change in hormone secretion.
  • Menopause: cessation of menstruation.
  • Follicles become less responsive to gonadotropins, reduce estrogen and progesterone secretion.
  • Uterus, vagina, and breasts atrophy; increased risk of vaginal infections, cardiovascular disease, and osteoporosis.

Oogenesis & Sexual Cycle

  • Reproductive cycle: fertilization to birth and return to fertility.
  • Sexual cycle: recurring monthly events when no pregnancy; ovarian and menstrual cycles.
  • Oogenesis: egg production, produces haploid gametes by meiosis.

Oogenesis Timeline

  • Female germ cells arise from yolk sac during embryonic development.
  • Oogonia multiply until the 5th month (~6-7 million), then arrest development.
  • Shortly before birth, oogonia transform into primary oocytes, proceed to early meiosis I.
  • Most undergo degeneration (atresia).
  • By puberty, ~200,000 oocytes remain.
  • FSH stimulates monthly cohorts of oocytes to continue development.
  • Meiosis I completes on ovulation day, producing a secondary oocyte and the first polar body.
  • Secondary oocyte proceeds to metaphase II, arrests until fertilization.
  • If fertilized, completes meiosis II and casts off a second polar body.

Sexual Cycle

  • Rhythmic changes in ovaries and uterus correlate with oogenesis and folliculogenesis; averages 28 days.
  • Hormonal control: hypothalamo-pituitary-ovarian axis.
  • Follicular phase (2 weeks): menstruation occurs, uterus replaces tissue, follicles grow.
  • Ovulation: around day 14, follicle becomes corpus luteum.
  • Luteal phase (2 weeks): corpus luteum stimulates endometrial secretion and thickening.
  • If no pregnancy, endometrium breaks down, menstruation begins again.

Ovarian Cycle

  • Follicular phase (day 1-14): FSH stimulates follicle growth and estradiol secretion.
  • Dominant follicle with richest blood supply.
  • Anterior pituitary produces LH surge, causing formation of the secondary oocyte.
  • Ovulation: rupture of mature follicle and egg release.
  • Luteal phase (day 15-28): corpus luteum forms, stimulated by LH to secrete estrogen and progesterone.
  • If no pregnancy, corpus luteum involutes around day 22, forming corpus albicans.
  • Estrogen and progesterone levels drop, FSH rises to stimulate new follicles.

Menstrual Cycle

  • Concurrent with the ovarian cycle.
  • Four phases: proliferative, secretory, premenstrual, menstrual.
  • Proliferative phase: rebuilding of the endometrium, stimulated by estrogen.
  • Secretory phase: endometrium thickens due to secretion and fluid accumulation, stimulated by progesterone.
  • Premenstrual phase: endometrial degeneration, corpus luteum atrophies, progesterone levels fall, causing ischemia.
  • Menstrual phase: menstrual fluid discharged from the vagina.

Female Sexual Response

  • Excitement: myotonia, vasocongestion, increased heart rate, blood pressure, and respiratory rate.
  • Plateau: uterus is tented, orgasmic platform constricts the penis, clitoris is engorged.
  • Orgasm: intense sensation, orgasmic platform contractions, uterine peristaltic contractions.
  • Resolution: body reverts back to normal.

Pregnancy & Childbirth

  • Gestation: average of 266 days from conception to childbirth.
  • Gestational calendar measured from the first day of the woman’s last menstrual period (LMP).
  • Birth predicted 280 days from LMP.
  • Divided into 3-month trimesters.

Hormones of Pregnancy

  • Estrogens, progesterone, human chorionic gonadotropin (HCG), human chorionic somatomammotropin.
  • Primarily secreted by the placenta, corpus luteum initially important.
  • HCG: secreted by blastocyst and placenta, stimulates corpus luteum.
  • Estrogens: increase to 30x normal, cause tissue growth in fetus and mother; relax pubic symphysis.
  • Progesterone: suppresses FSH/LH secretion, uterine contractions; promotes decidual cell proliferation; stimulates breast acini development.
  • Prolactin: promotes milk synthesis, inhibited by dopamine when not pregnant.