An increase in glomerular filtration rate (GFR) typically leads to:
Reduced blood pressure
No change in urine volume
Decreased urine production
Increased urine production
The Correct Answer is D
A. Reduced blood pressure: While a significant loss of fluid through high GFR can eventually lower blood volume, an increase in GFR is often a result of high blood pressure. High GFR itself does not immediately reduce pressure through a primary mechanism. It is a consequence of hemodynamics rather than a cause.
B. No change in urine volume: Renal physiology dictates that an increase in the filtered load typically results in a higher volume of fluid entering the tubules. Unless tubular reabsorption increases proportionally, the final urine volume must change. The volume of filtrate directly influences the volume of the end product.
C. Decreased urine production: This would only occur if the tubular reabsorption rates significantly exceeded the increased rate of filtration at the glomerulus. Under standard physiological conditions, a higher GFR provides more substrate for excretion. Decreased production is associated with low GFR or high ADH levels.
D. Increased urine production: A higher GFR elevates the volume of ultrafiltrate entering the proximal convoluted tubule each minute. This overwhelms the standard reabsorptive capacity of the nephrons, leading to a greater volume of fluid reaching the collecting ducts. Consequently, the total daily urine output increases significantly.
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Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is E
Explanation
A. Diabetic ketoacidosis: This metabolic state involves high concentrations of glucose and ketone bodies within the renal filtrate. These solutes increase the osmotic pressure and density of urine, leading to an elevated specific gravity. It reflects a state of solute excess rather than dilution.
B. Urinary tract infection (UTI): Bacterial colonization and the presence of white blood cells or nitrites typically increase urine turbidity and density. While infections alter chemical composition, they do not physiologically cause the profound dilution seen in low specific gravity. It usually results in normal or high density.
C. Dehydration: In response to fluid deficit, the kidneys maximize water reabsorption under the influence of antidiuretic hormone. This produces highly concentrated urine with a significantly elevated specific gravity. Low specific gravity is physiologically incompatible with a state of systemic fluid volume depletion.
D. Presence of protein: Proteinuria increases the mass of dissolved solids per unit volume of urine. Large molecules like albumin raise the density of the fluid as it passes through the collecting ducts. This finding is associated with higher, not lower, specific gravity measurements.
E. Overhydration: Excessive fluid intake suppresses antidiuretic hormone, leading to the excretion of a large volume of dilute urine. The renal tubules minimize water reabsorption, resulting in a urine density approaching that of pure water (1.000). This physiological state directly results in low specific gravity.
Correct Answer is D
Explanation
A. Hormones reduce the need for filtration during low activity: The metabolic need to clear wastes and maintain electrolyte balance is continuous. While hormones like ANP or Angiotensin II can modulate GFR, they do not eliminate the baseline requirement for stable filtration. Stability is maintained by local mechanisms.
B. The liver compensates for changes in renal pressure: The liver is not involved in the autoregulation of renal blood flow or glomerular pressure. Renal autoregulation is an intrarenal process that occurs independently of other organ systems. The kidney manages its own perfusion through local vascular responses.
C. Blood volume stays constant regardless of physical activity: Physical activity causes significant shifts in blood volume due to sweating and fluid redistribution to muscles. Despite these systemic changes, the kidney utilizes autoregulation to protect the glomerulus from fluctuations. Stable volume is a result, not the cause.
D. Intrinsic controls like myogenic and tubuloglomerular feedback adjust afferent arteriole tone: Autoregulation allows the kidney to maintain a constant GFR across a wide range of systemic blood pressures (80-180 mmHg). The myogenic response and feedback from the macula densa adjust afferent resistance to keep glomerular pressure steady.
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