Cerebral blood flow (CBF) is maintained at approximately 50 mL/100g/min over a wide range of mean arterial pressures (50–150 mmHg). The primary mechanism responsible for this autoregulation is:

• A Myogenic response: cerebral arterioles constrict with increased transmural pressure
• B Metabolic response: CO2-mediated vasodilation adjusting for metabolic needs
• C Neurogenic response: sympathetic innervation constrains vasodilation at high pressures
• D Both myogenic and metabolic mechanisms acting simultaneously ✓

Explanation

Cerebral autoregulation involves both myogenic and metabolic mechanisms operating simultaneously. The myogenic response (Bayliss effect) causes smooth muscle contraction in response to increased intraluminal pressure, limiting flow when MAP rises. Metabolically, local CO2 and H+ changes rapidly vasodilate/vasoconstrict arterioles: hypercapnia is the most potent cerebral vasodilator. Together these maintain CBF near 50 mL/100g/min across a MAP range of ~50–150 mmHg. Outside this range (e.g., malignant hypertension), autoregulation fails and CBF becomes pressure-dependent.

Reference: Guyton & Hall, Textbook of Medical Physiology, 14th ed.

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