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What mechanism is primarily responsible for the immediate regulation of blood pressure in response to changes in posture?

A.

Baroreceptor reflex

B.

Chemoreceptor reflex

C.

Release of antidiuretic hormone

D.

Renin-angiotensin-aldosterone system

Answer and Explanation

The Correct Answer is A

A. Baroreceptor reflex:
 Baroreceptors in the carotid sinus and aortic arch detect sudden changes in blood pressure due to posture changes. They initiate autonomic responses, increasing heart rate and vasoconstriction to maintain cerebral perfusion, preventing dizziness or syncope.

B. Chemoreceptor reflex:
 Chemoreceptors respond to blood oxygen, carbon dioxide, and pH, regulating ventilation more than immediate blood pressure changes.

C. Release of antidiuretic hormone:
 ADH acts more slowly to conserve water and increase blood volume; it is not responsible for immediate posture-related blood pressure changes.

D. Renin-angiotensin-aldosterone system:
 RAAS regulates blood pressure over minutes to hours via vasoconstriction and fluid retention; it does not act immediately during rapid postural changes.


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Related Questions

Correct Answer is A

Explanation

A. Left ventricle:
The left ventricle is the main pumping chamber of the systemic circulation, sending oxygenated blood through the aorta to all tissues. Its thick muscular walls generate the high pressure necessary for systemic perfusion.

B. Right ventricle:
The right ventricle pumps deoxygenated blood to the lungs via the pulmonary artery, not to the systemic circulation.

C. Left atrium:
The left atrium receives oxygenated blood from the lungs and delivers it to the left ventricle; it does not generate enough force for systemic circulation.

D. Right atrium:
The right atrium receives systemic venous blood and delivers it to the right ventricle; it does not pump oxygen-rich blood to the body.

Correct Answer is B

Explanation

A. Oxygen saturation:
Oxygen saturation affects tissue oxygen delivery but does not directly influence vascular resistance.

B. Blood vessel diameter:
Peripheral resistance is strongly influenced by vessel diameter. Vasoconstriction increases resistance and blood pressure, while vasodilation decreases resistance. This is a key determinant of systemic vascular resistance and blood pressure regulation.

C. Venous return:
Venous return affects preload and cardiac output, indirectly influencing blood pressure, but it does not directly determine peripheral resistance.

D. Heart rate:
Heart rate affects cardiac output but does not directly change peripheral resistance, which is primarily a function of arteriolar tone and vessel diameter.

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