Testes: Outside abdominal cavity in scrotal sac (2–2.5°C below body temp for spermatogenesis). Seminiferous tubules → sperm. Leydig cells → testosterone. Sertoli cells → nourish sperm, secrete inhibin.
Spermatogenesis: Spermatogonia (2n) → Primary spermatocyte (2n) [meiosis I] → Secondary spermatocyte (n) [meiosis II] → Spermatids (n) → Spermatozoa (n) by spermiogenesis.
Accessory glands: Seminal vesicle (60% semen volume — fructose for energy), Prostate (alkaline — neutralises vaginal acidity), Bulbourethral/Cowper's gland (lubrication).
Oogenesis: Begins in foetal life. Oogonia → Primary oocyte (2n) — arrested at Prophase I at birth. At puberty, LH surge → completes meiosis I → Secondary oocyte (n) + 1st polar body. Meiosis II completes only after fertilisation → ovum + 2nd polar body.
Fallopian tube: Site of fertilisation (ampullary-isthmic junction). Fimbriae collect the ovum from ovary. Ciliated epithelium moves ovum toward uterus.
Uterus: Pear-shaped, 7.5 cm long. Endometrium (inner lining) is shed during menstruation. Myometrium = muscular layer.
Menstrual phase (Days 1–5): Shedding of endometrium. Low estrogen and progesterone.
Follicular/Proliferative phase (Days 6–13): FSH stimulates follicle growth → rising estrogen → endometrium proliferates → LH surge on Day 13.
Ovulation (Day 14): LH surge → ovulation. Secondary oocyte released. Most fertile period.
Luteal/Secretory phase (Days 15–28): Corpus luteum forms from ruptured follicle → secretes progesterone + estrogen → endometrium thickens. If no fertilisation → corpus luteum degenerates → hormone drop → menstruation.
Menarche: First menstruation (puberty, ~11–13 years). Menopause: cessation (~45–55 years). Cycle absent during pregnancy.
Fertilisation: Occurs in ampullary region of fallopian tube. Acrosomal reaction (enzymes dissolve zona pellucida). Cortical reaction prevents polyspermy.
Cleavage: Mitotic divisions of zygote while moving to uterus. 2 cells → 4 → 8 (morula, 8–16 cells) → blastocyst (hollow ball).
Implantation: Blastocyst implants into endometrium on Day 7 after fertilisation (Day ~21 of menstrual cycle). Trophoblast invades endometrium.
Placenta: Forms from trophoblast + maternal decidua. Functions: Exchange of O₂, nutrients, waste. Secretes hCG (maintains corpus luteum), progesterone, estrogen, relaxin. hCG detected in urine → basis of pregnancy test.
Germ layers: Ectoderm → skin, nervous system, sense organs. Mesoderm → muscles, bones, circulatory system, kidneys, gonads. Endoderm → gut lining, liver, pancreas, respiratory tract.
Gestation: 9 months (266 days from fertilisation / 280 days from LMP). First trimester: organogenesis. Second: rapid growth, sex determination. Third: full term development.
Parturition: Oxytocin triggers uterine contractions. Positive feedback loop — stretch → more oxytocin → more contractions → birth. Relaxin (from corpus luteum/placenta) loosens pelvic ligaments.
Days 6–13: Follicular/Proliferative
Day 13: LH surge begins
Day 14: Ovulation
Days 15–28: Luteal/Secretory
Fertile window: Days 12–16
Detected in urine: basis of home pregnancy test
Maintains corpus luteum until placenta takes over
Peak: ~10 weeks gestation
Placenta secretes: progesterone, estrogen, hPL, relaxin
Secondary oocyte: arrested at Metaphase II (at ovulation)
Meiosis II completes: only after fertilisation
If no fertilisation: secondary oocyte degenerates
hCG (human Chorionic Gonadotropin) is produced by the trophoblast cells of the implanted blastocyst. It appears in urine very early in pregnancy and is the hormone detected by home pregnancy tests.
Oogenesis begins in foetal life. Primary oocytes are formed but arrested at Prophase I (diplotene stage) until puberty. At puberty, each month one primary oocyte resumes meiosis I in response to FSH/LH surge. Secondary oocyte (arrested at Metaphase II) is released at ovulation.
Fertilisation occurs in the ampullary region of the fallopian tube (oviduct), specifically at the ampullary-isthmic junction. The fertilised egg then undergoes cleavage while travelling to the uterus for implantation (takes ~7 days to reach uterus).
Gametogenesis: 1 Q/year
Fertilisation/implantation: 1 Q/year
Expected: Placenta functions, hCG
Watch: Sertoli vs Leydig cell functions