Table 51.1 — Mammalian reproductive hormones (memorize this one)
10 rows| Hormone | Source | Job in the MALE | Job in the FEMALE |
|---|---|---|---|
| GnRH | Hypothalamus | Makes the anterior pituitary release FSH and LH | Same — makes the anterior pituitary release FSH and LH |
| FSH | Anterior pituitary | Stimulates Sertoli cells → supports spermatogenesis | Stimulates follicle growth and estradiol secretion |
| LH | Anterior pituitary | Stimulates Leydig cells → testosterone secretion | Triggers ovulation, converts follicle → corpus luteum, drives its estradiol/progesterone |
| Testosterone | Leydig cells | Maintains secondary sex characteristics, accessory organs, spermatogenesis; inhibits LH and GnRH | — |
| Inhibin | Sertoli cells | Suppresses FSH only | — |
| Estradiol | Granulosa cells, then corpus luteum | — | Female secondary sex characteristics; builds the endometrium each month; triggers the LH surge midcycle |
| Progesterone | Corpus luteum | — | Completes uterine preparation for pregnancy; helps maintain secondary sex characteristics |
| hCG | Embryonic chorion | — | LH-like; maintains the corpus luteum in early pregnancy; detected by pregnancy tests |
| Oxytocin | Posterior pituitary | — | Uterine contraction and milk-ejection reflex |
| Prolactin | Anterior pituitary | — | Milk production |
The 28-day cycle — ovarian and uterine, side by side
5 rows| Days | Ovarian cycle | Uterine cycle | Hormones | Key event |
|---|---|---|---|---|
| 0–5 | Follicular phase begins | Menstruation | Estradiol and progesterone at their lowest; FSH starting to rise | Endometrium sheds with bleeding |
| 5–13 | Follicular phase — dominant follicle → Graafian follicle | Proliferative phase | FSH and LH rise gradually; estradiol climbs and peaks just before day 14 | Primary oocyte completes meiosis I → secondary oocyte + first polar body |
| 14 | Ovulation | Ovulation | LH surge (plus a small FSH bump); estradiol dips | Graafian follicle ruptures; secondary oocyte released, arrested at metaphase II |
| 15–25 | Luteal phase — corpus luteum active | Secretory phase | Progesterone rises sharply; estradiol rises a second time; both now inhibit FSH and LH | Endometrium becomes vascular, glandular, glycogen-rich for implantation |
| 26–28 | Luteal regression | Late secretory → menstruation | Estradiol and progesterone crash | Corpus luteum dies with no LH — unless hCG from an embryo rescues it |
Spermatogenesis vs oogenesis — every difference
10 rows| Feature | Spermatogenesis | Oogenesis |
|---|---|---|
| Gametes per precursor cell | 4 functional sperm | 1 ovum + up to 3 polar bodies |
| Cytokinesis | Equal | Unequal — the oocyte keeps almost all the cytoplasm |
| Timing | Continuous from puberty through most of life | Arrested twice; one oocyte finishes per cycle |
| First arrest | None | Primary oocyte in prophase I from before birth until ovulation |
| Second arrest | None | Secondary oocyte at metaphase II until fertilization |
| Meiosis II trigger | Automatic | Fertilization itself |
| Supply | Spermatogonia self-renew — never runs out | About 1 million follicles present at birth; the supply is fixed |
| Output rate | 100–200 million per day | Normally one egg per 28-day cycle |
| Support cells | Sertoli cells (nurse) and Leydig cells (testosterone) | Granulosa cells (estradiol) |
| Site | Seminiferous tubules of the testis | Ovarian follicles |
Semen — who contributes what
4 rows| Source | Share of volume | What it adds |
|---|---|---|
| Seminal vesicles (paired) | 60% | Fructose-rich fluid — fuel for sperm |
| Prostate gland | 30% | Milky alkaline fluid |
| Bulbourethral (Cowper’s) glands | 10% | Lubricates the urethra and penis tip before intercourse |
| Sperm themselves | ~1% | ~300 million cells in a 2–5 mL ejaculate; under 20 million/mL is considered sterile |
Birth control methods (Table 51.2) — failure = pregnancies per 100 users per year
11 rows| Method | Mechanism | Failure rate | Key drawback |
|---|---|---|---|
| Implant | Hormone capsule under the skin blocks ovulation | 0.05 | Irregular or absent periods; minor surgery to place and remove |
| Sterilization (vasectomy / tubal ligation) | Cuts and ties the vas deferens or Fallopian tubes | Nearly 0 | Reversal is expensive and often unsuccessful; rare spontaneous reconnection |
| IUD | Prevents implantation by irritation (copper or hormonal) | 1 | A third of users get cramps or bleeding; infection risk at insertion |
| Injectable | Hormone shot every 3 months blocks ovulation | 6 | Occasional heavy menstrual bleeding |
| Oral contraceptive | Progesterone analogs ± estrogen suppress FSH/LH → no ovulation | 9 typical, ~1 perfect use | Must be taken daily; risky for smokers over 35 |
| Diaphragm | Rubber cup covers the cervix and holds spermicide | 12 | Needs fitting; can dislodge |
| Condom | Sheath collects semen | 18 (3–20 range) | Needs cooperation and consistent use — but gives STD protection |
| Spermicides (foams, jellies, suppositories) | Chemically kill or block sperm | 10–28 | Must be applied 5–10 min before each act; messy |
| Morning-after pill | ~50× estrogen dose; blocks ovulation, fertilization, or implantation | 1–10% per use | Emergency use only — high dose, severe side effects possible |
| Douching | Rinsing the vagina after intercourse | ~40 | Can push sperm further into the uterus — actively counterproductive |
| Abstinence | No intercourse | 0 in principle | Hardest method to sustain |
Exam traps
11 pairsQuestions get built out of near-misses. If you can state each difference in one sentence, you will not lose those points.
*FSH*vs*LH*
FSH = Follicle growth and Sertoli cells. LH = Leydig cells and the Luteinizing surge that causes ovulation and makes the corpus Luteum. In both sexes FSH builds gametes and LH drives the steroid hormone.
*Ovarian* cyclevs*Uterine* cycle
Two names for the same 28 days seen from two organs. Ovarian = follicular / ovulation / luteal (what the ovary is doing). Uterine = menstrual / proliferative / secretory (what the lining is doing). Follicular pairs with proliferative; luteal pairs with secretory.
*Spermatogenesis*vs*Oogenesis*
Four equal sperm, continuous, never arrests. One egg plus three polar bodies, unequal division, arrested at prophase I until ovulation and again at metaphase II until fertilization.
*Graafian follicle*vs*Corpus luteum*
Same structure, before and after ovulation. Before: a fluid-filled follicle holding the oocyte, driven by FSH, secreting mostly estradiol. After: the ruptured shell converted by LH, secreting estradiol AND progesterone.
Estradiol as *positive* feedbackvsEstradiol as *negative* feedback
Follicular phase: rising estradiol stimulates the pituitary to fire the LH surge. Luteal phase: estradiol plus progesterone together inhibit FSH and LH. Same hormone, opposite sign, different phase — this is the classic exam trap.
*Primary* oocytevs*Secondary* oocyte
Primary = diploid, arrested in prophase I, sits inside the follicle for decades. Secondary = haploid, arrested at metaphase II, and it is the cell that actually gets ovulated. A true "ovum" only exists after fertilization.
*Ovoviviparity*vs*Viviparity*
Both keep the young inside and give live birth. The difference is the food source: ovoviviparity feeds the embryo on yolk; viviparity feeds it from maternal blood through a placenta.
*Estrous* cyclevs*Menstrual* cycle
Estrous mammals reabsorb the lining (no bleeding) and are receptive only around ovulation. Humans and apes shed it with bleeding and can be receptive any time. Proestrus/estrus/metestrus/diestrus map to proliferative/midcycle/secretory/menstrual.
*Protogyny*vs*Protandry*
Protogyny = "first female", so female → male (bluehead wrasse). Protandry = "first male", so male → female. The prefix names what the animal starts as.
*Sertoli* cellsvs*Leydig* cells
Sertoli sit inside the tubule wall, respond to FSH, nurse the sperm, and secrete inhibin. Leydig sit between the tubules (interstitial), respond to LH, and secrete testosterone.
*Vasectomy*vs*Tubal ligation*
Vasectomy cuts the vas deferens — sperm are still made but never enter semen. Tubal ligation cuts the Fallopian tubes — ovulation still happens but the oocyte cannot reach the uterus. Neither removes a gonad and neither changes hormone levels.