Reproduction
Human reproduction is sexual: haploid gametes made by meiosis fuse to restore the diploid number and produce a genetically unique individual. The PMDC MDCAT 2026 syllabus restricts this chapter to human reproduction only — the parts of the male and female reproductive systems and the hormones that control them, the menstrual cycle, and the common sexually transmitted diseases with their causative agents. Expect 2-4 MCQs, most of them on hormones.
Human Reproductive System
Both systems are built on the same plan: a pair of gonads that make gametes and sex hormones, a set of ducts that transport the gametes, and accessory glands or organs that support fertilisation and development. Both are controlled by the same hypothalamic-pituitary axis: GnRH from the hypothalamus → FSH and LH from the anterior pituitary → gonadal hormones.
Male reproductive system
- Testes (in the scrotum)
- Paired gonads. Seminiferous tubules carry out spermatogenesis; Sertoli (nurse) cells inside the tubules nourish the developing sperm, form the blood-testis barrier and secrete inhibin; Leydig (interstitial) cells between the tubules secrete testosterone.
- Scrotum
- Sac holding the testes outside the body cavity, keeping them about 2-3°C below core temperature — essential for normal sperm production.
- Epididymis
- Coiled tube on each testis where sperm mature (become motile and fertile) and are stored.
- Vas deferens (ductus deferens)
- Muscular duct that carries sperm from the epididymis to the ejaculatory duct by peristalsis. It is cut and tied in a vasectomy.
- Ejaculatory duct & urethra
- The ejaculatory duct opens into the urethra, which is the common passage for urine and semen in the male and runs through the penis.
- Penis
- Copulatory organ of erectile tissue that deposits semen in the vagina.
- Seminal vesicles — contribute roughly 60% of semen volume: alkaline, viscous fluid rich in fructose (energy for sperm) and prostaglandins (stimulate uterine contractions).
- Prostate gland — about 30% of the volume: thin, milky, alkaline fluid containing citrate and enzymes that help liquefy semen.
- Bulbourethral (Cowper's) glands — a small amount of clear alkaline mucus released before ejaculation; lubricates and neutralises acidic urine residue in the urethra.
The alkalinity matters: it protects sperm from the acidic environment of the vagina (pH ~3.5-4.5). A normal ejaculate is ~2-5 mL containing tens of millions of sperm per mL.
- GnRH (hypothalamus) → stimulates the anterior pituitary.
- FSH → acts on Sertoli cells, supporting spermatogenesis.
- LH (also called ICSH in males) → acts on Leydig cells to secrete testosterone.
- Testosterone → drives spermatogenesis and the secondary sexual characteristics (deep voice, facial and body hair, muscle and bone growth, growth of the reproductive organs); exerts negative feedback on GnRH and LH.
- Inhibin (Sertoli cells) → selectively inhibits FSH, fine-tuning the rate of sperm production.
Unlike the female cycle, male hormone secretion is continuous and non-cyclic, running from puberty into old age.
Female reproductive system
- Ovaries
- Paired gonads in the pelvic cavity. Carry out oogenesis and secrete oestrogen and progesterone. A girl is born with all her primary oocytes already formed and arrested in prophase I.
- Oviducts (fallopian tubes)
- Funnel-shaped fimbriae sweep the released oocyte in; ciliated, muscular tubes then move it towards the uterus. Fertilisation normally occurs in the ampulla (upper third) of the oviduct.
- Blocked or tied tubes (tubal ligation) prevent fertilisation; implantation inside the tube gives a dangerous ectopic pregnancy.
- Uterus (womb)
- Pear-shaped muscular organ where the embryo implants and develops. Wall layers: perimetrium (outer), myometrium (thick smooth muscle that contracts during labour) and endometrium (inner lining that thickens and is shed each cycle).
- Cervix
- Narrow neck of the uterus opening into the vagina; secretes mucus whose thickness changes across the cycle and dilates during childbirth.
- Vagina
- Muscular canal that receives semen, forms the birth canal and passes menstrual flow. Its acidic pH is protective against infection.
- Mammary glands
- Accessory organs that produce milk after childbirth under the control of prolactin (milk synthesis) and oxytocin (milk ejection / let-down).
- GnRH → anterior pituitary releases FSH and LH in a cyclic pattern.
- FSH → stimulates growth of ovarian follicles; the granulosa cells of the growing follicle secrete oestrogen.
- LH → a mid-cycle surge triggers ovulation and converts the ruptured follicle into the corpus luteum.
- Oestrogen → repairs and thickens the endometrium, produces the female secondary sexual characteristics; at high sustained levels it exerts positive feedback that causes the LH surge.
- Progesterone (corpus luteum, later placenta) → maintains and secretes into the endometrium, quietens the myometrium and inhibits FSH and LH so no new follicle develops.
- hCG (from the implanted embryo's chorion) → keeps the corpus luteum alive in early pregnancy; it is the hormone detected by pregnancy tests.
- Oxytocin → uterine contractions during labour and milk let-down; relaxin softens the cervix and pelvic ligaments near term.
Menstrual Cycle
The menstrual (female reproductive) cycle is the monthly series of changes that prepares an oocyte for release and the endometrium for implantation. Average length is 28 days (normal range 21-35). Day 1 is the first day of bleeding. It begins at menarche (~11-15 years) and ends at menopause (~45-55 years). Two cycles run in parallel — one in the ovary, one in the uterus — both driven by the same hormones.
Oestrogen and progesterone are at their lowest because the corpus luteum of the previous cycle has degenerated. Without progesterone support the endometrium breaks down and is shed as menstrual flow (blood, mucus and endometrial tissue, ~30-80 mL). The fall in these hormones removes the brake on the pituitary, so FSH begins to rise.
FSH stimulates several primary follicles; usually one becomes the dominant Graafian follicle. Its granulosa cells secrete increasing amounts of oestrogen, which proliferates (rebuilds and thickens) the endometrium and thins the cervical mucus. This is the phase of variable length — it is what makes some cycles longer than others.
High oestrogen now acts by positive feedback on the pituitary, producing a sharp LH surge (with a smaller FSH peak) around days 12-13. Roughly 24-36 hours later the Graafian follicle ruptures and releases a secondary oocyte, arrested at metaphase II, into the oviduct. Meiosis II is completed only if a sperm penetrates it. The oocyte survives ~24 hours; sperm survive ~3-5 days in the female tract.
Under LH the ruptured follicle becomes the corpus luteum, which secretes mainly progesterone plus some oestrogen. Progesterone makes the endometrium secretory — glandular, glycogen-rich and richly supplied with blood — ready for implantation, and raises basal body temperature by ~0.5°C. It also inhibits FSH and LH, preventing a second ovulation. This phase is fairly fixed at ~14 days.
- No fertilisation: the corpus luteum degenerates by about day 26 into the corpus albicans; progesterone and oestrogen fall; the endometrium is shed and the next cycle begins.
- Fertilisation: the implanted embryo secretes hCG, which rescues the corpus luteum so progesterone stays high, the endometrium is retained and menstruation stops. After ~3 months the placenta takes over hormone production.
| Days | Ovarian phase | Uterine phase | Dominant hormone(s) |
|---|---|---|---|
| 1–5 | Early follicular | Menstrual (shedding) | All ovarian hormones low; FSH rising |
| 6–13 | Follicular (Graafian follicle grows) | Proliferative (endometrium rebuilds) | Oestrogen rising |
| ~14 | Ovulation | Endometrium at full thickness | LH surge (triggered by peak oestrogen) |
| 15–28 | Luteal (corpus luteum) | Secretory (glandular, glycogen-rich) | Progesterone (+ oestrogen) |
Sexually Transmitted Diseases
Sexually transmitted diseases (STDs, also called STIs) spread mainly through sexual contact; several also pass through blood, contaminated needles, or from mother to child during pregnancy or birth. For MDCAT you must be able to match each disease to its causative agent and its main symptoms. Bacterial and protozoal STDs are curable with drugs; viral STDs are not curable, only controlled.
| Disease | Causative agent | Type | Main symptoms |
|---|---|---|---|
| Gonorrhoea | Neisseria gonorrhoeae | Bacterium | Thick yellow-green urethral or vaginal discharge, burning micturition (dysuria); may cause pelvic inflammatory disease (PID), sterility, and eye infection in newborns (ophthalmia neonatorum) |
| Syphilis | Treponema pallidum | Bacterium (spirochaete) | Primary: painless ulcer (chancre) at the site of infection. Secondary: skin rash including palms and soles, fever, swollen lymph nodes. Tertiary (years later): gummas, cardiovascular and nervous system damage; congenital syphilis in babies |
| Chlamydia | Chlamydia trachomatis | Bacterium | Often symptomless ("silent"); otherwise discharge, painful urination, lower abdominal pain; a leading cause of PID, ectopic pregnancy and infertility |
| Trichomoniasis | Trichomonas vaginalis | Protozoan (flagellate) | Frothy, foul-smelling yellow-green vaginal discharge, itching and soreness; often symptomless in males |
| Genital candidiasis (thrush) | Candida albicans | Fungus (yeast) | Thick white curd-like discharge, intense itching and inflammation |
| Genital herpes | Herpes simplex virus (mainly HSV-2) | Virus | Painful fluid-filled blisters and ulcers on the genitals, fever; the virus stays latent in nerve ganglia and recurs |
| Genital warts | Human papillomavirus (HPV) | Virus | Cauliflower-like warts (HPV 6, 11); high-risk types 16 and 18 cause cervical cancer — preventable by HPV vaccination |
| Hepatitis B | Hepatitis B virus (HBV) | Virus | Fatigue, nausea, jaundice, dark urine; chronic infection leads to cirrhosis and liver cancer. Vaccine available — a major public-health issue in Pakistan |
| AIDS | Human immunodeficiency virus (HIV) | Virus (retrovirus) | Destroys CD4 helper T-cells; long asymptomatic period, then fever, weight loss, chronic diarrhoea, swollen lymph nodes and opportunistic infections (tuberculosis, pneumonia, candidiasis) and Kaposi's sarcoma |
- Abstinence or a mutually faithful uninfected partner; barrier protection.
- Screening of blood before transfusion; sterile needles and instruments.
- Vaccination against hepatitis B and HPV.
- Early diagnosis and treating both partners — antibiotics for bacterial STDs, metronidazole for trichomoniasis, antifungals for candidiasis; antiviral therapy (ART for HIV) controls but does not cure viral STDs.
- Screening pregnant women to prevent mother-to-child transmission.
Worked MCQs
Five MCQs that capture the high-yield testing patterns for this chapter.
Q1. Testosterone in the human male is secreted by:
Leydig cells lie in the connective tissue between the seminiferous tubules and secrete testosterone under the influence of LH. Sertoli cells sit inside the tubules, nourish developing sperm and secrete inhibin; spermatogonia are the germ cells; the prostate is an accessory gland, not endocrine in this sense.
Q2. Fructose, the main energy source for sperm in semen, is secreted mainly by the:
The seminal vesicles contribute about 60% of semen volume and their alkaline secretion is rich in fructose and prostaglandins. The prostate adds a milky citrate- and enzyme-containing fluid; the bulbourethral glands add only lubricating mucus; the epididymis stores and matures sperm.
Q3. Ovulation in a normal 28-day menstrual cycle is triggered by a sharp rise in:
Peak oestrogen from the mature Graafian follicle acts by positive feedback on the pituitary, producing an LH surge around days 12-13; ovulation follows about 24-36 hours later, near day 14. FSH only peaks slightly, progesterone rises after ovulation from the corpus luteum, and hCG appears only if implantation occurs.
Q4. The corpus luteum secretes chiefly:
The corpus luteum forms from the ruptured follicle after ovulation and secretes mainly progesterone (with some oestrogen), which maintains the secretory endometrium. If fertilisation does not occur it degenerates into the corpus albicans, progesterone falls, and menstruation follows. hCG is made by the embryo, not the corpus luteum — it is what keeps the corpus luteum alive.
Q5. Syphilis is caused by:
Syphilis is caused by the spirochaete bacterium Treponema pallidum and begins as a painless chancre. Neisseria gonorrhoeae causes gonorrhoea, Trichomonas vaginalis is a protozoan causing trichomoniasis, and HSV-2 causes genital herpes with painful blisters.
Quick Recap
- Male: seminiferous tubules make sperm; Sertoli cells nourish + secrete inhibin; Leydig cells secrete testosterone; epididymis matures and stores sperm.
- Semen: seminal vesicles (~60%, fructose) + prostate (~30%, alkaline milky fluid) + bulbourethral glands (mucus).
- Male hormones: GnRH → FSH (Sertoli, spermatogenesis) and LH (Leydig, testosterone); inhibin inhibits FSH. Secretion is continuous, not cyclic.
- Female: ovaries (oogenesis, oestrogen + progesterone); fertilisation in the ampulla of the oviduct; implantation in the endometrium.
- Cycle phases: menstrual (1-5) → follicular/proliferative (1-13) → ovulation (~14) → luteal/secretory (15-28).
- FSH grows the follicle; oestrogen rebuilds the endometrium; the LH surge (positive feedback from peak oestrogen) causes ovulation; progesterone from the corpus luteum maintains the lining.
- No fertilisation → corpus luteum → corpus albicans → hormones fall → menstruation. Fertilisation → hCG rescues the corpus luteum.
- STDs: gonorrhoea (N. gonorrhoeae), syphilis (T. pallidum), chlamydia (C. trachomatis) — bacterial; trichomoniasis (T. vaginalis) — protozoan; candidiasis (C. albicans) — fungal; herpes (HSV-2), warts (HPV), hepatitis B (HBV), AIDS (HIV) — viral.