In haemorrhagic shock, the transcapillary refill mechanism restores plasma volume by:
- A Increased aldosterone-mediated renal sodium retention
- B Reduced capillary hydrostatic pressure causing net fluid absorption from interstitium ✓
- C Increased plasma oncotic pressure due to hepatic synthesis of albumin
- D Vasopressin-mediated aquaporin upregulation in collecting ducts
Correct answer: B. Reduced capillary hydrostatic pressure causing net fluid absorption from interstitium
Explanation
After haemorrhage, arteriolar vasoconstriction reduces capillary hydrostatic pressure. According to Starling forces, when hydrostatic pressure falls below oncotic pressure, net reabsorption of interstitial fluid into the capillary occurs — the 'transcapillary refill' that auto-transfuses up to 500–1000 mL within 30–60 minutes. This is the immediate compensatory mechanism; aldosterone and ADH operate on a slower time scale (hours).
Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.
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