🧪 Ovary & Follicular Development
Gross: Paired, almond‑shaped organs (~3 × 1.5 × 1 cm). Cortex houses follicles; medulla contains loose connective tissue and a rich vascular plexus.
Follicle stages (in brief)
- Primordial: primary oocyte (arrested in prophase I) + single layer of flattened granulosa cells.
- Primary: oocyte enlarges; granulosa cells become cuboidal and proliferate; zona pellucida appears.
- Secondary (antral): fluid‑filled spaces coalesce into an antrum; theca interna/externa form.
- Graafian (mature): large antrum; oocyte completes meiosis I (now haploid, 2N DNA) and arrests in metaphase II.
Key hormonal & cellular events
- Theca interna: synthesizes androgens → converted to estradiol by granulosa cells (aromatase).
- Granulosa cells: produce estrogen, inhibin; form gap junctions; secrete zona pellucida.
- LH surge triggers ovulation (around cycle day 14).
- Only ~400 oocytes ovulated; most undergo atresia.
Corpus luteum & luteolysis
- After ovulation, the ruptured follicle collapses → corpus luteum (granulosa lutein + theca lutein cells).
- Secretes progesterone (and estrogen) to maintain the endometrium.
- If no pregnancy: regresses in 10‑14 days → corpus albicans (fibrous scar).
- If pregnancy: hCG from the placenta sustains the corpus luteum for ~6 months.
Ovulation
→
Corpus luteum
→
Progesterone ↑
→
(if no hCG) → corpus albicans
🔬 Oviduct (Fallopian Tube)
Length: ~12 cm. Segments: infundibulum (fimbriae) → ampulla (usual fertilization site) → isthmus → intramural (uterine) portion.
Histology (3 layers)
- Mucosa: simple columnar epithelium (ciliated + secretory cells). Cilia beat toward uterus.
- Muscularis: inner circular + outer longitudinal smooth muscle.
- Serosa: visceral peritoneum.
Functions & transport
- Secretory cells produce nutrient‑rich fluid that activates sperm.
- Combined ciliary action + peristalsis move the ovum/zygote toward uterus.
- In immotile cilia syndrome (Kartagener’s), tubal transport remains normal (muscle compensates).
⚕️ Ectopic pregnancy: implantation in the ampulla (or elsewhere) — thin tubal wall leads to rupture and life‑threatening bleeding.
🏛️ Uterus & Endometrial Dynamics
Pear‑shaped organ: fundus (above oviduct entry), corpus (body), cervix (lower cylinder).
Layers
- Perimetrium (serosa/adventitia)
- Myometrium: smooth muscle bundles (hyperplasia/hypertrophy in pregnancy).
- Endometrium: mucosa with simple tubular glands.
Endometrial zones
- Functional layer (functionalis): sloughed during menstruation; regenerates from basalis.
- Basal layer (basalis): retained; contains stem cells for regeneration.
- Epithelium: ciliated + secretory simple columnar cells.
🌱 Vagina
Wall: mucosa (stratified squamous epithelium, rich in glycogen), muscularis (longitudinal smooth muscle), and adventitia.
- Vaginal mucus originates from cervical glands.
- Glycogen in epithelial cells is metabolized by lactobacilli to maintain acidic pH.
- No glands in the vaginal wall itself.
🤱 Mammary Glands
Alveoli (terminal secretory units) proliferate during pregnancy; lactation is driven by prolactin.
- During late pregnancy, plasma cells in the stroma secrete IgA → transferred to neonate (passive immunity).
- Most breast cancers (carcinomas) arise from lactiferous duct epithelium.
🔬 Pearl: Secretory IgA is the main immunoglobulin in breast milk.
⚕️ Clinical Correlates
Urethral & perineal trauma (male anatomy correlate)
- Bulb of penis injury: urine extravasates into superficial perineal space → can spread into scrotum, penis, and anterior abdominal wall (deep to Scarpa’s fascia).
- Often due to saddle injury or catheterization trauma.
Ectopic pregnancy – key facts
- Most common site: ampulla of oviduct.
- Risk factors: previous tubal damage, smoking, IUD, assisted reproduction.
- Presents with abdominal pain, vaginal bleeding; rupture causes hemorrhagic shock.
- Diagnosis: transvaginal ultrasound + β‑hCG.
Follicular atresia & ovarian reserve
- At birth: ~1–2 million follicles; by puberty ~400,000 remain.
- Only ~450 oocytes are ovulated; the rest undergo atresia (apoptosis).
- Anti‑Müllerian hormone (AMH) is a marker of ovarian reserve.
⭐ High‑Yield USMLE Pearls
Ovulation & meiosis
- Oocyte completes meiosis I just before ovulation (follicle → Graafian).
- Arrests in metaphase II until fertilization.
- Meiosis II completes only after sperm entry.
Corpus luteum hormones
- Granulosa lutein → progesterone & estrogen.
- Theca lutein → androstenedione & progesterone.
- Progesterone inhibits new follicle development.
Histology identification tips
- Oviduct: highly folded mucosa with ciliated columnar cells.
- Uterus (proliferative): straight tubular glands; secretory: coiled, tortuous glands.
- Vagina: stratified squamous epithelium with glycogen vacuoles.
- Breast (lactating): abundant alveoli with eosinophilic secretions.
📌 Expand: Follicular development timeline
- Prenatal: oogonia proliferate → enter meiosis I (arrested as primordial follicles).
- Puberty: each cycle several primordial follicles → primary → secondary (antral).
- Mid‑cycle (day 14): LH surge → ovulation of dominant follicle.
- After ovulation → corpus luteum (peak progesterone ~day 21).
🧪 Lab & imaging correlates
- CT abdomen: key landmarks at T11–L4 (aorta, IVC, spleen, stomach, kidneys).
- Barium enema used for colonic evaluation; not directly reproductive but relevant in abdominal imaging.
- Pelvic ultrasound is first‑line for ovarian follicles, endometrial thickness, ectopic pregnancy.