What is the primary role of the renin-angiotensin-aldosterone system in blood pressure regulation?
To increase blood volume and systemic vascular resistance
To decrease heart rate and reduce cardiac output
To regulate oxygen levels in the blood
To control nerve impulses to the heart
The Correct Answer is A
A. To increase blood volume and systemic vascular resistance:
The RAAS system increases blood pressure by two main mechanisms: angiotensin II causes vasoconstriction, raising systemic vascular resistance, and aldosterone promotes sodium and water retention, increasing blood volume. Together, these actions restore perfusion pressure in hypotensive states.
B. To decrease heart rate and reduce cardiac output:
RAAS does not directly affect heart rate; it works primarily on vascular tone and fluid retention, not cardiac chronotropy.
C. To regulate oxygen levels in the blood:
Oxygen sensing is mainly controlled by chemoreceptors, not RAAS.
D. To control nerve impulses to the heart:
RAAS does not directly regulate cardiac conduction or nerve impulses; it acts on vascular smooth muscle and renal sodium retention.
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Correct Answer is B
Explanation
A. To transport oxygen-rich blood to the systemic circulation:
The aorta and systemic arteries carry blood to the body; coronary arteries are specific to the myocardium.
B. To supply the heart muscle with oxygen and nutrients:
Coronary arteries deliver oxygenated blood and essential nutrients to the myocardium, supporting continuous contraction. Blockage leads to ischemia, angina, or myocardial infarction.
C. To regulate blood pressure in the pulmonary circulation:
Pulmonary circulation is regulated by the pulmonary artery, veins, and right heart function, not the coronary arteries.
D. To remove carbon dioxide from the systemic circulation:
Carbon dioxide removal occurs via the lungs, not the coronary arteries.
Correct Answer is D
Explanation
A. By increasing the threshold for myocardial depolarization:
While ischemia can affect depolarization, the primary effect of CAD is not a generalized change in the threshold of myocardial cells; instead, conduction problems occur due to localized ischemia.
B. By increasing the heart rate through sympathetic stimulation:
CAD does not inherently increase heart rate. Tachycardia may occur as a compensatory response, but it is not the primary mechanism by which CAD affects the conduction system.
C. By enhancing electrical conductivity in the myocardium:
CAD does not improve conduction. In fact, ischemia impairs conduction by damaging cardiac cells, which can lead to arrhythmias.
D. By causing ischemia to the sinoatrial and atrioventricular nodes:
CAD reduces blood flow through coronary arteries, which can lead to ischemia in the SA and AV nodes, causing bradyarrhythmias, heart blocks, or conduction delays. This is a direct consequence of insufficient oxygen supply to the conduction tissue.
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