Renal Physiology and Filtration Practice Quiz (11 questions)

1. Which structures together make up a nephron, the functional unit of the kidney?

A. The renal corpuscle, collecting duct, renal pelvis, and distal convoluted tubule

B. The renal corpuscle, proximal convoluted tubule, loop of Henle, and distal convoluted tubule

C. The renal pelvis, ureter, collecting duct, and renal artery

D. The glomerulus, renal pelvis, proximal tubule, and ureter

Answer: (B)

Explanation

A nephron comprises the renal corpuscle, proximal convoluted tubule, loop of Henle, and distal convoluted tubule. The collecting duct and renal pelvis are not included in this listed set of nephron components.

2. A nephron has a short loop of Henle that barely enters the medulla. Which type of nephron is it?

A. A cortical nephron, whose loop extends little or not at all into the medulla

B. A juxtamedullary nephron, whose loop remains largely in the cortex

C. A cortical nephron, whose loop extends deeply into the medulla

D. A juxtamedullary nephron, whose loop extends deeply into the medulla

Answer: (A)

Explanation

Cortical nephrons have short loops of Henle that penetrate little or not at all into the medulla. Juxtamedullary nephrons have long loops that extend deeply into the medulla.

3. Which arrangement describes the glomerular filtration barrier?

A. Fenestrated endothelial cells, a single basement membrane, and podocytes whose pedicels form filtration slits

B. Fenestrated endothelial cells, a single basement membrane, and smooth muscle cells forming filtration pores

C. Continuous endothelial cells, two basement membranes, and podocytes whose pedicels form filtration slits

D. Fenestrated endothelial cells, a double basement membrane, and podocytes whose cell bodies form filtration slits

Answer: (A)

Explanation

The barrier consists of fenestrated capillary endothelial cells, one basement membrane, and podocytes with pedicels that form filtration slits. The alternative involving continuous endothelium is incorrect because the glomerular endothelial cells are fenestrated.

4. If glomerular blood pressure rises while oncotic and hydrostatic pressures remain unchanged, what happens to effective filtration pressure?

A. It decreases because blood pressure opposes filtration while the other pressures promote it

B. It increases because blood pressure promotes filtration while the other pressures oppose it

C. It remains unchanged because the three pressures contribute equally to filtration

D. It decreases because oncotic pressure promotes filtration while blood pressure opposes it

Answer: (B)

Explanation

Effective filtration pressure is blood pressure minus oncotic and hydrostatic pressures, so raising blood pressure increases it when the opposing pressures are unchanged. The alternative that treats blood pressure as opposing filtration reverses its role.

5. What does glomerular filtration rate (GFR) quantify?

A. The volume of plasma filtered by the glomeruli per unit time

B. The volume of plasma cleared of a substance by tubular secretion

C. The volume of blood supplied to the kidneys per unit time

D. The volume of urine excreted by the kidneys per unit time

Answer: (A)

Explanation

GFR quantifies how much plasma is filtered through the glomeruli over time and is used to assess kidney function. Renal plasma flow describes blood plasma delivered to the kidneys, not the portion filtered.

6. If PAH clearance is 540 mL/min and PAH extraction is about 90%, what renal plasma flow is estimated?

A. About 540 mL/min

B. About 486 mL/min

C. About 900 mL/min

D. About 600 mL/min

Answer: (D)

Explanation

Because PAH extraction is about 90%, renal plasma flow is estimated by dividing PAH clearance by 0.9, giving 600 mL/min. Using the clearance value without adjusting for incomplete extraction would underestimate renal plasma flow.

7. What is the primary role of renal intrinsic autoregulation in blood pressure control?

A. To stabilize renal plasma flow and GFR despite changes in arterial pressure

B. To increase sodium excretion whenever arterial pressure rises

C. To maintain systemic arterial pressure by adjusting cardiac output

D. To redirect blood from the kidneys to vital organs during normal pressure changes

Answer: (A)

Explanation

Intrinsic autoregulation helps maintain renal plasma flow and GFR through myogenic responses and tubuloglomerular feedback, mainly by altering afferent arteriolar resistance. Redirecting blood to vital organs is associated with sympathetic regulation when pressure falls below the autoregulatory range.

8. A substance is filtered at the glomerulus and then reabsorbed from tubular fluid into the peritubular blood; how does its clearance compare with GFR?

A. It is above GFR because reabsorption adds the substance to urine.

B. It equals GFR because filtration determines its clearance.

C. It is below GFR because reabsorption reduces urinary excretion.

D. It is unrelated to GFR because clearance measures plasma volume.

Answer: (C)

Explanation

Reabsorption returns some filtered substance to the blood, so less appears in urine and its clearance is below GFR. Secretion, the most plausible alternative mechanism, adds substance to tubular urine and can raise clearance above GFR.

9. How does tubular secretion differ from tubular excretion in the described renal processes?

A. Secretion is synthesis in the tubular wall, while excretion transfers substances from blood into tubular urine.

B. Secretion moves substances from tubular urine into blood, while excretion involves glomerular filtration.

C. Secretion transfers substances from blood into tubular urine, while excretion is synthesis in the tubular wall.

D. Secretion reabsorbs bicarbonate into blood, while excretion synthesizes ammonia in the collecting duct.

Answer: (A)

Explanation

Tubular secretion refers to synthesis of substances in the tubular wall, whereas tubular excretion describes transfer from blood into tubular urine. Excretion is not the synthesis process; it is the movement of a substance into the urine.

10. How does proximal tubular solute reabsorption lead to obligatory water reabsorption?

A. Reabsorbed solutes create an osmotic effect that draws water from the tubular fluid.

B. Reabsorbed solutes stimulate Na/K-ATPase to pump water into the peritubular blood.

C. Solute uptake reduces plasma oncotic pressure, causing water to enter the tubule.

D. Solute transport raises tubular pressure, forcing water through the glomerular filtration barrier.

Answer: (A)

Explanation

Reabsorption of solutes from proximal tubular fluid creates an osmotic driving force for water to follow. Na/K-ATPase helps establish gradients for solute transport, but it does not directly pump water.

11. A patient has a blood glucose concentration of about 2 g/L. What would a urine test most likely show as filtered glucose begins to exceed tubular reabsorption?

A. Glucose appearing in the urine as reabsorption becomes incomplete

B. Glucose appearing because it is no longer filtered at the glomerulus

C. No urinary glucose because reabsorption has reached its transport maximum

D. Reduced urinary glucose because glucose transport into blood has increased

Answer: (A)

Explanation

At about 2 g/L, filtered glucose begins to exceed the tubules’ capacity to reabsorb it all, so glucose starts appearing in urine. Reaching the transport maximum, when further filtered glucose is excreted, occurs at a higher blood glucose concentration, around 3.5 g/L.