Zoology · Ch 7 — Human Reproduction
Summary
Summary
- Male reproductive system: Testes (in scrotum, 2-3 degrees Celsius cooler) house seminiferous tubules for spermatogenesis; Leydig cells secrete testosterone; Sertoli cells nourish sperm. Epididymis stores/matures sperm; vas deferens, ejaculatory duct, urethra form the duct system. Accessory glands (seminal vesicles, prostate, bulbourethral) add seminal fluid — fructose, prostaglandins, clotting enzymes, alkaline buffer.
- Female reproductive system: Ovaries produce ova, secrete estrogen & progesterone. Oviduct (fallopian tube) has infundibulum (fimbriae catch ovum), ampulla (fertilisation site), isthmus. Uterus has perimetrium, myometrium (strong contractions), endometrium (menstrual shedding). Cervix leads to vagina. Mammary glands: alveoli (milk secretion) → lactiferous ducts.
- Gametogenesis: Spermatogenesis (seminiferous tubules) — spermatogonia (2n) → mitosis → primary spermatocytes (2n) → meiosis I → secondary spermatocytes (n) → meiosis II → spermatids (n) → spermiogenesis → spermatozoa. Oogenesis (ovary) — oogonia (2n) → primary oocyte (2n, arrested in prophase I) → at puberty, one per month completes meiosis I → secondary oocyte (n, arrested in metaphase II) + first polar body; fertilisation triggers meiosis II.
- Structure of sperm: Head (acrosome with hydrolytic enzymes, haploid nucleus), neck (mitochondria), middle piece (mitochondrial spiral for energy), tail (flagellum for motility).
- Menstrual cycle (~28 days): Menstrual phase (days 1–5, endometrium sheds), follicular phase (days 6–13, FSH stimulates follicle growth, estrogen rises, endometrium thickens), ovulation (day 14, LH surge releases secondary oocyte), luteal phase (days 15–28, corpus luteum secretes progesterone to maintain endometrium; if no pregnancy, corpus luteum degenerates → progesterone drop → menstruation).
- Fertilisation: Occurs in ampulla of oviduct. Sperm capacitation in female tract; acrosome reaction releases enzymes to penetrate corona radiata & zona pellucida. Cortical reaction prevents polyspermy. Sperm nucleus enters ovum; haploid nuclei fuse (syngamy) → zygote (2n).
- Implantation & pregnancy: Zygote undergoes cleavage (morula → blastocyst). Blastocyst implants in endometrium ~7 days after fertilisation. Trophoblast forms chorion (secretes hCG to maintain corpus luteum); inner cell mass forms embryo. Placenta develops from chorionic villi & uterine tissue — exchanges nutrients, gases, wastes; secretes hCG, hPL, estrogen, progesterone. …