Ovaries

Paired almond-shaped organs (~3 cm long) that serve dual endocrine and reproductive functions. Each ovary contains approximately 1-2 million oocytes at birth, declining to ~300,000-400,000 by puberty. Only about 400-500 will undergo ovulation during a woman's reproductive lifespan. Ovaries produce estradiol, progesterone, and small amounts of testosterone.

• Follicle development begins ~290 days before ovulation (primordial recruitment)
• Antral follicle count (AFC) visible on ultrasound correlates with ovarian reserve
• Blood supply via ovarian arteries (from abdominal aorta) and uterine arteries
• Ovarian volume decreases with age: ~6-7 cm³ in reproductive years to <2 cm³ post-menopause

Fallopian Tubes (Oviducts)

Paired muscular tubes (~10-12 cm) connecting each ovary to the uterus. The fimbriae (finger-like projections) sweep the released oocyte into the tube. Fertilization occurs in the ampulla (widest section), while ciliated epithelial cells and peristaltic contractions transport the embryo toward the uterus over 3-4 days.

• Four anatomical segments: interstitial, isthmus, ampulla, infundibulum
• Cilia beat at ~1,200 strokes/minute to propel the egg
• Tubal factor accounts for 25-35% of female infertility
• Ectopic pregnancy occurs when embryo implants in tube (~2% of pregnancies)

Uterus

Pear-shaped muscular organ (~7 cm long, 4 cm wide) with three layers: perimetrium (outer), myometrium (muscular middle), and endometrium (inner lining). The endometrium undergoes cyclical changes in response to estrogen and progesterone, building a receptive environment for implantation during the secretory phase.

• Endometrial thickness of 7-14 mm is optimal for implantation
• The "window of implantation" opens approximately 6-10 days post-ovulation
• Blood supply via uterine arteries (branches of internal iliac)
• Uterine anomalies (septate, bicornuate) affect 3-5% of women and can impact fertility

Cervix

Lower cylindrical portion of the uterus connecting to the vagina. Produces mucus that varies in consistency across the menstrual cycle. Fertile-quality cervical mucus (clear, stretchy, "egg-white" consistency) facilitates sperm transport and can sustain sperm viability for up to 5 days. Post-ovulatory mucus becomes thick and hostile to sperm.

• Spinnbarkeit (stretchiness) of cervical mucus peaks at ovulation
• Cervical crypts act as sperm reservoirs, releasing sperm in waves
• Cervical mucus filters abnormal sperm, allowing only ~1% to pass
• Cervical factor infertility accounts for ~3-5% of cases

Testes

Paired ovoid organs (~4 cm x 3 cm x 2.5 cm) housed in the scrotum, which maintains temperature 2-4°C below core body temperature—essential for spermatogenesis. Each testis contains ~250 lobules with ~600-1,200 seminiferous tubules where sperm are produced. Leydig cells (interstitial) produce testosterone; Sertoli cells nurture developing sperm.

• Spermatogenesis takes approximately 64-72 days from spermatogonia to mature sperm
• Daily sperm production: ~100-300 million per day in healthy males
• Testosterone production: ~5-7 mg/day, regulated by hypothalamic-pituitary-gonadal axis
• Testicular volume <12 mL is associated with reduced sperm production

Epididymis

Coiled tubular structure (~6 meters uncoiled) attached to each testis. Sperm spend 2-12 days traversing the epididymis, during which they acquire motility and fertilizing capacity. The cauda (tail) serves as a storage reservoir for mature sperm. Epididymal fluid provides nutrients and modifies the sperm surface.

• Three regions: caput (head), corpus (body), cauda (tail)
• Sperm acquire forward motility and zona pellucida binding ability here
• Epididymal obstruction is a correctable cause of obstructive azoospermia
• Sexual abstinence >5-7 days can decrease sperm quality due to prolonged storage

Accessory Glands

Seminal vesicles contribute ~60-70% of semen volume (fructose, prostaglandins, fibrinogen). Prostate gland adds ~20-30% (zinc, citric acid, PSA, proteolytic enzymes). Bulbourethral glands (Cowper's) produce pre-ejaculatory fluid for lubrication and pH buffering. Total ejaculate volume is typically 1.4-5 mL.

• Seminal fructose provides energy substrate for sperm motility
• Prostatic zinc has antibacterial properties and stabilizes chromatin
• Semen pH of 7.2-8.0 neutralizes vaginal acidity (pH 3.5-4.5)
• Initial ejaculate fraction (prostatic) contains highest sperm concentration

Menstrual Phase

Duration: | Days: Days 1-5

Shedding of the endometrial lining due to withdrawal of progesterone from the regressing corpus luteum. FSH begins to rise, initiating recruitment of a cohort of antral follicles (typically 6-12 follicles). This phase marks the beginning of a new cycle.

Follicular Phase

Duration: | Days: Days 6-13

Dominant follicle selection occurs by days 5-7, growing from ~2 mm to ~20 mm at ovulation. Rising estradiol from the dominant follicle triggers negative feedback on FSH (causing atresia of non-dominant follicles) and positive feedback on LH as it approaches 200 pg/mL. Endometrium proliferates (proliferative phase) from ~1 mm to 8-14 mm.

Ovulation

Duration: | Days: Day 14 (variable, range 11-21)

The LH surge triggers completion of meiosis I in the oocyte, cumulus expansion, follicular wall thinning, and stigma formation. Ovulation occurs 36-40 hours after LH surge onset. The oocyte is released with surrounding cumulus cells (corona radiata) into the peritoneal cavity, captured by fimbriae within minutes.

Luteal Phase

Duration: | Days: Days 15-28

The collapsed follicle transforms into the corpus luteum, producing progesterone (peak ~8 days post-ovulation, 10-20 ng/mL) and estradiol. Progesterone converts the endometrium to its secretory phase, developing spiral arteries and glycogen-rich glands essential for implantation. The luteal phase is remarkably consistent at 12-14 days.

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