(a) Describe the anatomy of uterus under the following headings: (i) Gross features (ii) Relations of uterus (iii) Ligaments and…

(a) Anatomy of the uterus

(i) Gross features: pear-shaped, thick-walled muscular organ about 7.5 × 5 × 2.5 cm, weighing 30–40 g. Parts: fundus (above tubal openings), body, isthmus and cervix (supravaginal and vaginal parts). Normally anteverted (about 90° to the vagina) and anteflexed (about 125° at the isthmus). Wall: endometrium, myometrium, perimetrium.

(ii) Relations:

• Anteroinferior (vesical) surface: uterovesical pouch and the bladder.
• Posterosuperior (intestinal) surface: rectouterine pouch (Douglas) with ileum and sigmoid colon, rectum behind.
• Lateral: broad ligament, uterine vessels, and the ureter about 2 cm lateral to the supravaginal cervix.
• Cervix: bladder in front (no peritoneum), rectouterine pouch and rectum behind, vagina below.

(iii) Ligaments and supports:

• Primary (muscular and fibromuscular): pelvic diaphragm and perineal body, transverse cervical (cardinal, Mackenrodt), uterosacral and pubocervical ligaments, and the angle of anteversion.
• Secondary (peritoneal folds): broad ligament, round ligament (maintains anteversion), uterovesical and rectovaginal folds.

(iv) Blood supply: uterine artery (anterior division of internal iliac) runs medially in the base of the broad ligament, crosses above the ureter ("water under the bridge") near the cervix, then ascends tortuously along the side of the uterus and anastomoses with the ovarian artery. Veins form the uterine plexus draining to the internal iliac veins.

(v) Lymphatic drainage:

• Fundus and upper body: para-aortic nodes (with ovarian vessels), and from the cornu along the round ligament to superficial inguinal nodes.
• Lower body: external iliac nodes.
• Cervix: external iliac, internal iliac (including obturator) and sacral nodes.

(vi) Applied aspects: uterine prolapse from weakness of cardinal and uterosacral supports after childbirth, ureteric injury while clamping the uterine artery in hysterectomy, lower-segment caesarean section through the isthmus, retroversion, fibroids, spread of carcinoma cervix to pelvic nodes, and the rectouterine pouch as the site for collection of pus or blood (culdocentesis).

(b) Short-term and long-term regulation of arterial pressure

Short-term (seconds to minutes, mainly neural):

• Baroreceptor reflex: carotid sinus and aortic arch stretch receptors signal via glossopharyngeal and vagus nerves to the nucleus tractus solitarius. A rise in pressure increases vagal and reduces sympathetic outflow, lowering heart rate, contractility and peripheral resistance, and vice versa. It buffers moment-to-moment changes, such as on standing, but resets within days.
• Chemoreceptor reflex: carotid and aortic bodies respond to hypoxia, hypercapnia and acidosis when pressure falls below about 80 mm Hg, raising sympathetic tone.
• CNS ischaemic response: powerful sympathetic vasoconstriction when medullary blood flow falls (Cushing reflex with raised intracranial pressure).
• Others: atrial (Bainbridge) reflexes, catecholamines, stress relaxation and capillary fluid shift.

Long-term (hours to days, mainly renal):

• Renal–body fluid mechanism (pressure natriuresis): a rise in pressure increases sodium and water excretion until volume and pressure return to the set point. This has near-infinite gain and is the dominant long-term controller.
• Renin–angiotensin–aldosterone system: low renal perfusion, sympathetic stimulation or low sodium at the macula densa release renin. Angiotensin II causes vasoconstriction, sodium retention, aldosterone and ADH release and thirst. Aldosterone increases distal sodium reabsorption.
• ADH (vasopressin): water retention and vasoconstriction in haemorrhage.
• Natriuretic peptides (ANP, BNP): natriuresis and vasodilatation when atria are stretched.

(c)(i) Initiation of eukaryotic protein synthesis and inhibitors

Initiation:

1. eIF2-GTP binds Met-tRNAi (not formylated) to form the ternary complex, which joins the 40S subunit with eIF1, eIF1A and eIF3 to form the 43S pre-initiation complex.
2. eIF4F (4E cap-binding, 4G scaffold, 4A helicase) binds the 5′ cap, with poly(A)-binding protein circularising the mRNA, and recruits the 43S complex (48S complex).
3. The complex scans 5′ to 3′ using ATP to the first AUG in a Kozak context.
4. eIF5 triggers GTP hydrolysis on eIF2, factors are released, and eIF5B-GTP joins the 60S subunit to form the 80S initiation complex with Met-tRNAi in the P site. eIF2B recycles eIF2-GDP (a control point via eIF2α phosphorylation).

Inhibitors:

• Cycloheximide: inhibits peptidyl transferase of the 60S subunit (eukaryotes).
• Diphtheria toxin: ADP-ribosylates eEF2, blocking translocation.
• Ricin: removes an adenine from 28S rRNA, inactivating the 60S subunit.
• Puromycin: aminoacyl-tRNA analogue that causes premature chain release (both kingdoms).
• Antibacterial: tetracycline (blocks aminoacyl-tRNA at the 30S A site), chloramphenicol (50S peptidyl transferase), streptomycin (30S, misreading), erythromycin (50S, translocation).

(c)(ii) Radioimmunoassay

Principle: competitive binding. A fixed, limited amount of specific antibody is incubated with a fixed amount of radiolabelled antigen (¹²⁵I or ³H) and the sample containing unlabelled antigen. Both compete for antibody sites, so the more unlabelled antigen, the less labelled antigen is bound. Bound and free fractions are separated (second antibody, charcoal, solid phase), radioactivity is counted, and the concentration is read from a standard curve. It is very sensitive (picogram range) and specific. Applications: hormones (insulin, T3, T4, TSH, cortisol, hCG, growth hormone), drug levels (digoxin), tumour markers (AFP, CEA, PSA), vitamins (B12, folate), viral antigens such as HBsAg, and research. It is now largely replaced by ELISA and chemiluminescence because of radiation hazards and isotope disposal.