(a) Describe the prostate under the following headings: (i) Gross features (ii) Lobes (iii) Capsules and ligaments (iv) Blood…

(a) Prostate

Gross features: a chestnut-shaped fibromuscular and glandular organ weighing about 20 g, lying below the bladder, in front of the rectal ampulla and behind the pubic symphysis. It has a base at the bladder neck, an apex resting on the urogenital diaphragm, and anterior, posterior and two inferolateral surfaces. The prostatic urethra passes through it, and the ejaculatory ducts pierce its posterior part. Its posterior surface is palpable on digital rectal examination.

Lobes: anatomically it has five lobes: anterior (isthmus), middle (between the urethra and ejaculatory ducts), posterior, and right and left lateral. McNeal's zones (peripheral, central, transitional, anterior fibromuscular stroma) are used clinically.

Capsules and ligaments: the true capsule is the thin fibrous condensation of the gland itself; the false capsule is the pelvic (visceral) fascia around it, with the prostatic venous plexus between them. Puboprostatic ligaments fix it to the pubis, and the lateral ligaments (of the levator ani) support it.

Blood supply: the inferior vesical artery mainly, plus the middle rectal and internal pudendal arteries. The prostatic venous plexus drains to the internal iliac veins and communicates with the vertebral plexus.

Lymphatic drainage: chiefly to the internal iliac nodes, and also to the external iliac and sacral nodes.

Age changes: it grows at puberty under androgens; after about 50 years the transitional zone enlarges (benign prostatic hyperplasia), whereas carcinoma arises mostly in the peripheral zone, and corpora amylacea and calculi increase.

(b) Ovarian cycle and ovulation tests

The ovarian cycle (28 days) is driven by hypothalamic GnRH, pituitary FSH and LH and ovarian steroids. In the follicular phase (days 1–14), FSH recruits follicles and stimulates granulosa cells to convert thecal androgens (made under LH) into oestradiol. A dominant follicle emerges, and rising oestradiol at first exerts negative feedback on FSH. Sustained high oestradiol (about 36–48 h) turns to positive feedback and triggers the LH surge, which completes meiosis I, ruptures the follicle and causes ovulation about 10–12 h after the LH peak (around day 14). In the luteal phase, the ruptured follicle forms the corpus luteum under LH, secreting mainly progesterone and some oestradiol, which prepare the endometrium and inhibit gonadotrophins. Unless hCG rescues it, the corpus luteum regresses after about 14 days, hormones fall and menstruation follows.

Tests for ovulation: basal body temperature (a rise of 0.3–0.5°C after ovulation); urinary LH kits; serial transvaginal ultrasound follicular tracking; mid-luteal serum progesterone (above about 3 ng/mL, around day 21); and endometrial biopsy showing secretory changes.

(c)(i) Polymerase chain reaction

Principle: in vitro enzymatic amplification of a chosen DNA segment by repeated cycles of heating and cooling, using two primers flanking the target, dNTPs, Mg²⁺ and a heat-stable DNA polymerase (Taq). Steps in each cycle: denaturation (about 94–95°C) separates the strands; annealing (50–65°C) lets primers bind; extension (72°C) lets Taq synthesise new strands. Each cycle doubles the product, so 30 cycles give about 10⁹ copies, detected by gel electrophoresis or by fluorescence in real-time PCR. RNA targets need prior reverse transcription.

Applications: diagnosis of infections such as tuberculosis, HIV viral load and SARS-CoV-2 (RT-PCR); prenatal and genetic diagnosis (for example sickle cell disease, cystic fibrosis); oncology (detecting BCR-ABL and other mutations); forensic and paternity DNA profiling; and HLA typing.

(c)(ii) Vitamin B₆ vitamers

Vitamin B₆ exists as three vitamers, pyridoxine (alcohol), pyridoxal (aldehyde) and pyridoxamine (amine), and their 5′-phosphates. The active coenzyme is pyridoxal phosphate (PLP), which is bound to enzymes through a Schiff base with lysine.

Roles in metabolism: transamination (ALT, AST); decarboxylation to make GABA, serotonin, dopamine, histamine and catecholamines; transsulfuration (cystathionine synthase and lyase); δ-aminolevulinate synthase in haem synthesis; kynureninase in niacin synthesis from tryptophan; glycogen phosphorylase in glycogenolysis; and serine palmitoyltransferase in sphingolipid synthesis.