Human Physiology

• Testes: produce sperm (spermatogenesis) and testosterone
• Seminiferous tubules: site of sperm production within testes
• Interstitial (Leydig) cells: produce testosterone (male sex hormone)
• Epididymis: sperm maturation and storage
• Vas deferens: tube carrying sperm from epididymis to urethra
• Prostate gland and seminal vesicles: produce seminal fluid (fructose for energy, alkaline to neutralise vaginal acidity)
• Urethra: shared passage for sperm and urine (but not simultaneously)
• Penis: delivers sperm into female reproductive tract

• Ovaries: produce eggs (oogenesis) and hormones (oestrogen, progesterone)
• Follicles: develop within ovaries; each contains an oocyte (immature egg)
• Oviducts (fallopian tubes): site of fertilisation; cilia and peristalsis move the egg towards the uterus
• Uterus: site of implantation and fetal development; lining (endometrium) thickens each cycle
• Cervix: neck of the uterus; produces mucus
• Vagina: receives sperm; birth canal

Spermatogenesis (in males)

• Occurs in seminiferous tubules of the testes
• Begins at puberty, continues throughout life
• Spermatogonia (2n) → primary spermatocytes → [meiosis I] → secondary spermatocytes → [meiosis II] → spermatids → sperm (n)
• One spermatogonium produces four functional sperm cells
• Controlled by FSH (stimulates spermatogenesis) and testosterone (from Leydig cells, stimulated by LH)

Oogenesis (in females)

• Begins before birth; oocytes arrest in prophase I
• At puberty: each cycle, typically one follicle matures
• Oogonium (2n) → primary oocyte → [meiosis I, completed at ovulation] → secondary oocyte (n) + first polar body → [meiosis II, completed only if fertilised] → ovum + second polar body
• One oogonium produces one functional egg (and 2–3 polar bodies)

The menstrual cycle (~28 days) is controlled by four hormones:

Phases

1. Menstruation (Days 1–5): Low hormone levels; endometrium sheds
2. Follicular phase (Days 1–14): FSH → follicle develops → oestrogen rises → endometrium rebuilds
3. Ovulation (Day ~14): LH surge triggers release of secondary oocyte
4. Luteal phase (Days 14–28): Corpus luteum produces progesterone → maintains endometrium
5. If no fertilisation: corpus luteum degenerates → progesterone drops → endometrium breaks down → menstruation

Feedback Interactions

• Early follicular phase: low oestrogen inhibits FSH and LH (negative feedback)
• Mid-cycle: high oestrogen levels trigger positive feedback → LH surge → ovulation
• Luteal phase: progesterone inhibits FSH and LH (negative feedback) → no new follicle develops

• Fertilisation occurs in the oviduct (fallopian tube)
• Sperm undergo capacitation in the female tract (activation/membrane changes)
• Sperm penetrate the corona radiata and zona pellucida of the egg
• Acrosome reaction: enzymes from the acrosome digest the zona pellucida
• Cortical reaction: after one sperm enters, the egg releases cortical granules → hardens the zona pellucida → prevents polyspermy (blocks other sperm)
• Nuclei of sperm and egg fuse → zygote (2n)

From Fertilisation to Implantation

• Zygote divides by mitosis → 2 cells → 4 → 8 → morula → blastocyst
• Blastocyst travels to uterus (~6-7 days after fertilisation)
• Implantation: blastocyst embeds in the endometrium
• Trophoblast (outer layer) develops into the placenta
• Inner cell mass develops into the embryo

• HCG (human chorionic gonadotropin): produced by the embryo/placenta; maintains the corpus luteum → continued progesterone production → endometrium maintained
• Placenta (fully developed by ~12 weeks): takes over production of oestrogen and progesterone
• Functions of the placenta:
  • Gas exchange (O₂ to fetus, CO₂ from fetus)
  • Nutrient transfer (glucose, amino acids)
  • Waste removal (urea)
  • Hormone production (progesterone, oestrogen, HCG)
  • Acts as a barrier (though some pathogens like rubella, HIV, and Zika can cross)
• Maternal and fetal blood do not mix — exchange occurs across the thin placental membrane by diffusion, osmosis, and active transport

• Controlled by positive feedback involving oxytocin:
  1. Fetal head pushes against cervix
  2. Stretch receptors send signals to the brain
  3. Posterior pituitary releases oxytocin
  4. Oxytocin stimulates uterine muscle contractions
  5. Contractions push baby further against cervix → more oxytocin → stronger contractions
  6. Positive feedback loop continues until delivery
  7. After birth, the stimulus is removed and the loop stops

Question: Explain the roles of FSH and LH in the menstrual cycle. (4 marks)

Solution: FSH (follicle-stimulating hormone) is released by the anterior pituitary gland. It stimulates the development of a follicle in the ovary. The developing follicle produces oestrogen, which causes the endometrium to thicken. LH (luteinising hormone) is also released by the anterior pituitary. A surge in LH around day 14 triggers ovulation — the release of the secondary oocyte from the mature follicle. LH also stimulates the empty follicle to develop into the corpus luteum, which produces progesterone to maintain the endometrium.

• Male system: testes (sperm + testosterone), vas deferens, prostate, penis.
• Female system: ovaries (eggs + oestrogen/progesterone), oviducts, uterus, vagina.
• Spermatogenesis: 4 sperm per meiosis; continuous. Oogenesis: 1 egg per meiosis; cyclical.
• Menstrual cycle: FSH → follicle → oestrogen → LH surge → ovulation → corpus luteum → progesterone → negative feedback.
• Fertilisation: acrosome reaction, cortical reaction prevents polyspermy; zygote → blastocyst → implantation.
• Placenta: gas exchange, nutrients, waste removal, hormones; maternal and fetal blood don't mix.
• Birth: oxytocin positive feedback loop drives increasingly strong contractions.