Human Reproduction — Formula Sheet

$T_{\text{testes}}$: Temperature of the testes (°C) · $T_{\text{body}}$: Normal internal body temperature (°C)

The testes lie outside the abdominal cavity in the scrotum, which keeps them 2–2.5 °C below normal internal body temperature — needed for spermatogenesis.

Seminiferous tubules are lined by spermatogonia and Sertoli cells. Leydig (interstitial) cells lie outside the tubules and secrete androgens.

Spermatogonia multiply by mitosis; some become primary spermatocytes (2n = 46), which undergo meiosis. Spermatids become sperms by spermiogenesis; release of sperms from the tubules is spermiation.

$N_{\text{sperms}}$: Number of sperms (equal to number of spermatids) · $N_{\text{primary}}$: Number of primary spermatocytes · $N_{\text{secondary}}$: Number of secondary spermatocytes

Each primary spermatocyte gives 4 sperms; each secondary spermatocyte gives 2. Number of spermatids = number of sperms.

GnRH from the hypothalamus makes the anterior pituitary release LH and FSH. Androgens stimulate spermatogenesis; FSH makes Sertoli cells secrete factors that help spermiogenesis.

Both conditions must hold for normal fertility. Seminal plasma comes from the seminal vesicles, prostate and bulbourethral glands.

Both divisions are unequal: the oocyte keeps the bulk of the nutrient-rich cytoplasm. Meiosis I finishes in the tertiary follicle; meiosis II finishes only after a sperm enters.

$N_{\text{ova}}$: Number of ova formed · $N_{\text{primary oocytes}}$: Number of primary oocytes completing oogenesis

One ovum per primary oocyte, compared with four sperms per primary spermatocyte. The extra nuclei go into polar bodies.

Only 60,000–80,000 primary follicles are left in each ovary at puberty. The tertiary follicle has a fluid-filled cavity called the antrum; the secondary oocyte forms the zona pellucida.

NCERT gives the average interval between menstruations as about 28/29 days. One ovum is released in the middle of each cycle. The reproductive cycle of female primates (monkeys, apes, humans) is the menstrual cycle. Menarche is the first menstruation at puberty; menopause is around 50 years of age.

Menstrual flow lasts 3–5 days. The follicular (proliferative) phase regenerates the endometrium; the luteal phase is when the corpus luteum is active. Day numbers are for an idealised 28-day cycle.

The LH surge ruptures the Graafian follicle. Progesterone from the corpus luteum maintains the endometrium. With no fertilisation the corpus luteum degenerates, the endometrium breaks down and menstruation follows.

All ova carry X; half the sperms carry X and half carry Y. So the father's sperm decides the sex, with a 50% chance of each.

Fertilisation happens in the ampullary region of the oviduct. Cleavage (mitosis) starts as the zygote moves through the isthmus towards the uterus.

The trophoblast attaches to the endometrium; the inner cell mass becomes the embryo. Embedding of the blastocyst in the endometrium is implantation, which leads to pregnancy.

Levels of estrogens, progestogens, cortisol, prolactin and thyroxine also rise in maternal blood during pregnancy. Relaxin comes from the ovary, not the placenta.

First movements of the foetus and hair on the head usually appear in the fifth month. By 24 weeks (end of the second trimester) the body has fine hair, eyelids separate and eyelashes form.

The signal comes from the fully developed foetus and the placenta. Oxytocin causes stronger contractions, which cause more oxytocin release — a positive loop until the baby is delivered.