What is the primary role of astrocytes in the brain's circulatory system?
Ensuring all brain areas receive an equal amount of blood flow.
Enhancing oxygen delivery by dilating blood vessels.
Regulating blood pressure within the brain's arteries.
Forming a protective barrier around brain capillaries to prevent harmful substance entry.
The Correct Answer is D
A. Ensuring all brain areas receive an equal amount of blood flow: Astrocytes do not directly distribute blood equally throughout the brain. Blood flow is regionally regulated based on neuronal activity through neurovascular coupling, rather than a uniform distribution enforced by astrocytes.
B. Enhancing oxygen delivery by dilating blood vessels: While astrocytes can influence local vasodilation through signaling to smooth muscle cells in nearby arterioles, their role is modulatory rather than directly enhancing oxygen delivery. The primary effect is part of neurovascular coupling, not a broad oxygenation mechanism.
C. Regulating blood pressure within the brain's arteries: Systemic and cerebral arterial blood pressure is controlled mainly by the autonomic nervous system and baroreceptors, not astrocytes. Astrocytes act locally at the capillary level rather than controlling overall cerebral arterial pressure.
D. Forming a protective barrier around brain capillaries to prevent harmful substance entry: Astrocytes are a critical component of the blood-brain barrier (BBB). Their end-feet enwrap capillaries, supporting tight junction formation in endothelial cells and restricting passage of toxins, pathogens, and large molecules, thereby protecting neuronal tissue and maintaining the brain’s tightly regulated microenvironment.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is B
Explanation
A. Diastolic pressure is the higher number in a blood pressure reading: In a standard blood pressure measurement (e.g., 120/80 mmHg), the systolic value is the higher number and reflects peak arterial pressure during ventricular contraction. Diastolic pressure is the lower value, representing arterial pressure when the heart is at rest between beats.
B. Diastolic pressure occurs when the heart is relaxed between beats: Diastolic pressure reflects the arterial pressure during ventricular relaxation (diastole). During this phase, the ventricles fill with blood, and the elastic recoil of the arteries maintains baseline pressure in the circulation, ensuring continuous perfusion of tissues.
C. Systolic pressure occurs during ventricular relaxation, and diastolic pressure occurs during ventricular contraction: Systolic pressure corresponds to ventricular contraction (systole), when blood is ejected into the aorta, producing the highest arterial pressure. Diastolic pressure occurs during ventricular relaxation, not contraction.
D. Systolic pressure represents the lower value in a blood pressure reading: Systolic pressure is the higher value because it reflects the force generated when the left ventricle contracts and propels blood into systemic circulation. The lower value is diastolic pressure, maintained by arterial elasticity and peripheral resistance during cardiac relaxation.
Correct Answer is D
Explanation
A. To inhibit aldosterone release from the adrenal cortex: Angiotensin II does not inhibit aldosterone; in fact, it stimulates aldosterone secretion from the adrenal cortex. Aldosterone then promotes sodium and water reabsorption in the kidneys, contributing to increased blood volume and pressure, which is the opposite of inhibition.
B. To reduce thirst and limit fluid intake: Angiotensin II actually stimulates thirst through action on the hypothalamus, encouraging fluid intake to help restore blood volume. Reducing thirst is not part of its physiological role in the renin-angiotensin-aldosterone system (RAAS).
C. To decrease blood pressure by stimulating sodium excretion: Angiotensin II does the opposite—it promotes sodium reabsorption in the distal tubules and collecting ducts via aldosterone. Sodium retention increases extracellular fluid volume, which raises blood pressure rather than decreasing it.
D. To increase blood pressure by promoting vasoconstriction and fluid retention: Angiotensin II is a potent vasoconstrictor, narrowing arterioles to elevate systemic vascular resistance. It also stimulates aldosterone release, leading to sodium and water retention, which increases blood volume. Together, these mechanisms raise blood pressure and maintain perfusion during hypotensive states.
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