How does decreased tubular reabsorption affect renal clearance?
It increases renal clearance by allowing more excretion
It has no direct impact on renal clearance
It increases tubular secretion
It decreases renal clearance by reducing excretion
The Correct Answer is A
A. It increases renal clearance by allowing more excretion: Renal clearance is a measure of how effectively the kidneys remove a substance from the plasma. If less of a filtered substance is reabsorbed into the blood, more remains in the urine. Consequently, the clearance rate increases.
B. It has no direct impact on renal clearance: Clearance is mathematically defined by the ratio of urinary excretion to plasma concentration. Since reabsorption directly determines how much of the filtered load is returned to circulation, any change in reabsorption significantly alters the clearance.
C. It increases tubular secretion: Reabsorption and secretion are distinct physiological processes involving different transport proteins. A decrease in the movement of substances out of the tubule does not inherently trigger an increase in the movement of substances into the tubule. They are independent variables.
D. It decreases renal clearance by reducing excretion: Reducing the reabsorption of a solute prevents it from returning to the peritubular capillaries. This leads to a higher concentration of the solute in the final urine. Therefore, excretion is enhanced, which increases the calculated renal clearance.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
A. True: The afferent arteriole has a significantly larger diameter than the efferent arteriole, creating a unique "bottleneck" effect. This anatomical arrangement generates the high hydrostatic pressure (approximately 55 mmHg) necessary to drive ultrafiltration. It is a fundamental principle of renal hemodynamics.
Correct Answer is D
Explanation
A. Acetylcholine: This neurotransmitter is primarily associated with the parasympathetic nervous system and cholinergic transmission. In the vasculature, it often promotes vasodilation through nitric oxide release rather than vasoconstriction. It does not mediate the renal sympathetic stress response.
B. Insulin: This anabolic hormone regulates glucose uptake and lipid metabolism in peripheral tissues. While it has some minor hemodynamic effects, it is not a mediator of the acute sympathetic fight-or-flight response. It does not cause significant afferent arteriolar constriction.
C. Cortisol: As a glucocorticoid, cortisol assists in long-term stress adaptation and blood pressure maintenance by upregulating adrenergic receptors. However, it is not the primary catecholamine responsible for immediate, acute vasoconstriction during sympathetic activation. Its effects are primarily genomic and slower.
D. Epinephrine: Secreted by the adrenal medulla during sympathetic stimulation, this catecholamine binds to alpha-1 adrenergic receptors on vascular smooth muscle. This induces profound vasoconstriction of the afferent arterioles to divert blood toward vital organs. This reduces GFR during systemic stress.
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