Precapillary sphincters are

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muscle cells that surround the capillary at its origin with the arteriole.

A. Decreased glomerular filtration rate (GFR) and reduced urine output: A decrease in GFR typically occurs in response to low blood pressure or renal hypoperfusion, not increased blood pressure. Elevated blood pressure tends to increase glomerular hydrostatic pressure, promoting filtration rather than reducing it.

B. No change in GFR due to homeostatic mechanisms: While the kidneys have autoregulatory mechanisms, such as afferent arteriole constriction, that help maintain GFR within a normal range, an immediate rise in systemic blood pressure can temporarily increase GFR before these mechanisms fully compensate.

C. Increased urine concentration without affecting blood volume: Increased urine concentration occurs when antidiuretic hormone (ADH) acts on the nephron, usually in response to dehydration or low blood volume. It does not represent the direct effect of elevated blood pressure on kidney filtration.

D. Increased GFR, leading to higher urine output and lower blood volume: When blood pressure rises, glomerular hydrostatic pressure increases, directly enhancing filtration. This results in more filtrate formation, higher urine output, and consequently a reduction in blood volume, representing the kidney’s immediate response to elevated systemic pressure through direct filtration regulation.

A. 25 mmHg: Pulse pressure is calculated as systolic minus diastolic pressure. A normal pulse pressure is approximately 30–40 mmHg. With a systolic pressure of 160 mmHg, a pulse pressure of 25 mmHg would be considered narrow, suggesting reduced stroke volume, increased systemic vascular resistance, or conditions such as heart failure or aortic stenosis.

B. 40 mmHg: A pulse pressure of 40 mmHg falls within the normal expected range for most adults. Even with an elevated systolic pressure of 160 mmHg, a 40 mmHg difference would not be considered narrow and generally reflects adequate stroke volume.

C. 50 mmHg: A pulse pressure of 50 mmHg is wider than normal and may indicate increased stroke volume or decreased arterial compliance, as seen in conditions like aortic regurgitation or aging arteries.

D. 45 mmHg: A pulse pressure of 45 mmHg is slightly above the typical normal range and would be considered normal to mildly widened. It does not represent a low or narrow pulse pressure in the context of a systolic pressure of 160 mmHg.