10.2 Repro_Male gonad_Oogenesis & Female Hypothalamic-Pituitary-Gonadal Axis

MALE GONAD

Testes functions are spermatogenesis and testosterone secretion, requiring a scrotal temperature of ~35–36°C, like a factory that only runs if the room is cooled properly; seminiferous tubules (80%) make sperm, while interstitial tissue (20%) with Leydig cells makes testosterone.

SEMINIFEROUS TUBULES & SERTOLI CELLS

Spermatogonia → primary spermatocytes → spermatids → spermatozoa (haploid), while Sertoli cells form the blood–testis barrier, nourish cells, secrete tubule fluid, phagocytose defects, bind testosterone, and release inhibin to ↓ FSH, like supervisors controlling production and security.

LEYDIG CELLS

Leydig cells secrete testosterone, are active in fetal life, quiet after birth, restart at puberty, and decline with age, like a generator turned back on during adolescence.

OOGENESIS

Females are born with all oocytes arrested in prophase I

follicles contain the oocyte plus follicular/granulosa cells that secrete estrogen, progesterone, inhibin, and relaxin.

FEMALE HPG AXIS

GnRH → FSH & LH, where LH stimulates theca cells to make progesterone and testosterone (converted to estrogen in granulosa cells via aromatase) and FSH stimulates granulosa cells to make estrogen plus inhibin/activin, like a thermostat with feedback.

MENSTRUAL CYCLE CONTROL

Cyclical estrogen and progesterone control ovarian and uterine changes, and menstruation occurs when these hormones fall, like setting and clearing a table each month.