Physiology & Biochemistry · single question
All of the following are physiological mechanisms that regulate blood pressure EXCEPT:
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Correct answer: C. Increase in portal vein pressure
Blood pressure is regulated by cardiac output (heart rate × stroke volume), peripheral vascular resistance, the renin-angiotensin-aldosterone system (RAAS), sympathetic nervous system tone, and antidiuretic hormone (ADH). Increased portal vein pressure is a consequence of portal hypertension (e.g., liver cirrhosis) and is not a physiological mechanism for blood pressure regulation. Portal hypertension actually leads to complications like esophageal varices and ascites, not systemic blood pressure control. The other options are all established components of blood pressure homeostasis.
- A. Stroke volume × heart rate = cardiac output, the other direct determinant of arterial pressure. Baroreceptor reflexes adjust both within seconds.
- B. Renin release triggers the renin–angiotensin–aldosterone system: angiotensin II causes vasoconstriction and aldosterone drives sodium and water retention, raising blood pressure. This is the principal long-term regulator.
- C. Peripheral vascular resistance is one of the two direct determinants of arterial pressure (BP = cardiac output × total peripheral resistance). Arteriolar tone is adjusted continuously by sympathetic outflow.
- D. CORRECT as the EXCEPTION. PORTAL VEIN PRESSURE belongs to the hepatic portal circulation, a low-pressure venous system draining the gut to the liver. It is not part of systemic arterial pressure regulation. Portal hypertension is a CONSEQUENCE of hepatic disease (cirrhosis, thrombosis) and produces ascites, varices and splenomegaly — it does not regulate systemic blood pressure.
Note: BP = cardiac output × total peripheral resistance. Short-term control is baroreceptor/sympathetic; long-term control is renal (RAAS and pressure natriuresis). Portal pressure sits entirely outside that loop.
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