Renal Physiology Practice Questions

Q: In which region of the nephron are P cells (principal cells) located?

Collecting duct. **Explanation:** The correct answer is **D. Collecting duct.** **1. Why the Collecting Duct is Correct:** Principal cells (P cells) are the predominant cell type found in the **late distal tubule** and throughout the **collecting duct**. Their primary physiological role is the regulation of water and electrolyte balance under hormonal control: * **Sodium (Na+) Reabsorption:** They reabsorb Na+ via Epithelial Sodium Channels (ENaC). * **Potassium (K+) Secretion:** They are the main site for K+ secretion into the tubular lumen. * **Water Reabsorption:** They express Aquaporin-2 (AQP2) receptors, which are regulated by **Antidiuretic Hormone (ADH/Vasopressin)**. * **Aldosterone Action:** Aldosterone acts primarily on P cells to increase Na+ reabsorption and K+ secretion. **2. Why Other Options are Incorrect:** * **A. PCT:** This region is lined by cells with a prominent brush border (microvilli) for bulk reabsorption of glucose, amino acids, and ions. It does not contain P cells. * **B. Loop of Henle:** The thin segments consist of simple squamous epithelium, while the Thick Ascending Limb (TAL) contains cuboidal cells specialized for the Na+-K+-2Cl- cotransporter (NKCC2). * **C. DCT:** The early DCT contains "DCT cells" specialized for the Na+-Cl- symporter (NCC). While P cells begin to appear in the late (connecting) tubule, the collecting duct is their definitive and most characteristic location. **3. High-Yield Clinical Pearls for NEET-PG:** * **Intercalated Cells (I cells):** Also found in the collecting duct, these are responsible for acid-base balance (**Type A** secretes H+; **Type B** secretes HCO3-). * **Liddle’s Syndrome:** Caused by overactivity of ENaC channels in P cells, leading to hypertension and hypokalemia. * **Potassium-Sparing Diuretics:** Amiloride and Triamterene work by blocking ENaC channels in the P cells, while Spironolactone antagonizes the aldosterone receptor within these same cells.

Q: What is the exact number of solutes transported in the thick ascending limb of the Loop of Henle per carrier pump?

Transports one Na+, one K+, and two Cl-.. ### Explanation The correct answer is **A: Transports one Na+, one K+, and two Cl-**. **Underlying Concept:** The thick ascending limb (TAL) of the Loop of Henle is known as the "diluting segment" of the nephron. The primary transport mechanism on the apical (luminal) membrane is the **NKCC2 symporter** (Sodium-Potassium-2-Chloride co-transporter). This carrier protein moves four ions simultaneously into the cell: **one sodium (Na+), one potassium (K+), and two chloride (Cl-) ions**. This process is **electroneutral**, meaning the net charge moved across the membrane by the pump itself is zero (1+ + 1+ - 2 = 0). This transporter utilizes the sodium gradient created by the basolateral Na+/K+ ATPase to drive the secondary active transport of these solutes. **Analysis of Incorrect Options:** * **Options B, C, and D:** These are incorrect because they misstate the stoichiometry of the NKCC2 pump. Any ratio other than 1:1:2 would violate the electroneutrality of this specific symporter and does not align with the physiological structure of the SLC12A1 protein (the gene encoding NKCC2). **High-Yield Clinical Pearls for NEET-PG:** * **Loop Diuretics:** Drugs like **Furosemide** and Torsemide act by specifically inhibiting the NKCC2 symporter. * **Bartter Syndrome:** A genetic defect in the NKCC2 transporter (Type 1) or the ROMK channel (Type 2) mimics the effect of chronic loop diuretic use, leading to hypokalemia, metabolic alkalosis, and hypercalciuria. * **Lumen-Positive Potential:** While the pump is electroneutral, some K+ leaks back into the lumen via **ROMK channels**, creating a +10 to +20 mV potential. This "lumen-positive" charge is the driving force for the **paracellular reabsorption** of divalent cations like **Calcium (Ca2+) and Magnesium (Mg2+)**.

Q: Glucose is absorbed through the apical membrane of the proximal convoluted tubule by which transporter?

SGLT-2. **Explanation:** The reabsorption of glucose in the kidney occurs almost entirely in the **Proximal Convoluted Tubule (PCT)**. This process involves two distinct steps: transport across the apical (luminal) membrane and transport across the basolateral membrane. **Why SGLT-2 is correct:** Glucose is transported across the **apical membrane** against its concentration gradient via **Secondary Active Transport**. This is mediated by **SGLT-2** (Sodium-Glucose Co-transporter 2), which couples the movement of one sodium ion with one glucose molecule. SGLT-2 is a high-capacity, low-affinity transporter located in the early part (S1 segment) of the PCT, responsible for reabsorbing approximately **90%** of filtered glucose. **Analysis of Incorrect Options:** * **SGLT-1:** This is a low-capacity, high-affinity transporter located in the late PCT (S3 segment). It reabsorbs the remaining 10% of glucose. It is also the primary transporter for glucose absorption in the small intestine. * **GLUT-2:** This is a **Facilitated Diffusion** transporter located on the **basolateral membrane** of the early PCT. It moves glucose out of the cell into the interstitium. * **GLUT-1:** This transporter is located on the basolateral membrane of the late PCT (S3 segment), working in conjunction with SGLT-1. **High-Yield Clinical Pearls for NEET-PG:** 1. **Renal Threshold for Glucose:** Glucose begins to appear in the urine (glycosuria) when blood glucose levels exceed **180 mg/dL**. 2. **Tubular Transport Maximum ($T_m$):** The transport system becomes fully saturated at a plasma glucose level of approximately **375 mg/min** in men. 3. **SGLT-2 Inhibitors (Gliflozins):** Drugs like Dapagliflozin inhibit SGLT-2 and are used in treating Type 2 Diabetes to promote glucose excretion in urine.

Q: A 20-year-old male patient presents with a decrease in urinary output to about 400ml/day. Both renal blood flow (RBF) and glomerular filtration rate (GFR) were decreased. Which of the following causes a decrease in both RBF and GFR?

Constriction of the afferent arteriole. **Explanation:** The Glomerular Filtration Rate (GFR) and Renal Blood Flow (RBF) are primarily regulated by the resistance of the afferent and efferent arterioles. **Why Option C is Correct:** **Constriction of the afferent arteriole** increases resistance *before* the blood reaches the glomerulus. This leads to: 1. **Decreased RBF:** Increased total renal vascular resistance reduces blood flow into the kidney. 2. **Decreased GFR:** Reduced flow into the glomerular capillaries lowers the glomerular hydrostatic pressure ($P_{GC}$), which is the primary driving force for filtration. **Analysis of Incorrect Options:** * **Option A (Dilation of efferent arteriole):** Decreases resistance to outflow. This **increases RBF** (less resistance) but **decreases GFR** because the "back pressure" in the glomerulus drops. * **Option B (Dilation of afferent arteriole):** Decreases resistance to inflow. This **increases both RBF and GFR** (due to increased $P_{GC}$). * **Option D (Constriction of efferent arteriole):** Increases resistance to outflow. This **decreases RBF** but **increases GFR** (up to a point) because it increases the hydrostatic pressure ($P_{GC}$) within the glomerular capillaries. **High-Yield Clinical Pearls for NEET-PG:** * **NSAIDs** inhibit prostaglandins (which normally dilate the afferent arteriole), leading to **afferent constriction** and a drop in GFR. * **ACE Inhibitors** prevent the action of Angiotensin II (which preferentially constricts the efferent arteriole), leading to **efferent dilation** and a drop in GFR. * **Key Rule:** If both RBF and GFR move in the **same** direction, the primary change is at the **afferent** arteriole. If they move in **opposite** directions, the primary change is at the **efferent** arteriole.

Q: A 78-year-old man presents with nausea and vomiting. On examination, he appears dehydrated, his abdomen is soft, and the jugular venous pressure is not elevated. Laboratory tests reveal hypernatremia, and his calculated free water deficit is approximately 3 L. In which part of the normal kidney is most of the water reabsorbed?

Proximal tubule. **Explanation:** The correct answer is **B. Proximal tubule**. In a normal kidney, approximately **65-70% of the filtered water** is reabsorbed in the **Proximal Convoluted Tubule (PCT)**. This process is known as **obligatory water reabsorption**. It occurs isosmotically, meaning water follows the active reabsorption of solutes (primarily sodium via the Na+/K+ ATPase pump) through aquaporin-1 channels and paracellular pathways to maintain osmotic equilibrium. **Why other options are incorrect:** * **Collecting ducts:** While this is the site of **facultative water reabsorption** regulated by Antidiuretic Hormone (ADH), it only accounts for about 5-10% of total water reabsorption. It is crucial for final urine concentration but not for the bulk of volume recovery. * **Distal tubule:** The early distal tubule is part of the "diluting segment" and is relatively impermeable to water. * **Ascending loop of Henle:** This segment (specifically the Thick Ascending Limb) is **impermeable to water**. It actively reabsorbs solutes (Na+/K+/2Cl-) without water, which is essential for creating the medullary osmotic gradient. **High-Yield Clinical Pearls for NEET-PG:** * **PCT:** Always reabsorbs a constant fraction of filtered load (Glomerulotubular balance). * **Descending Loop of Henle:** Highly permeable to water but impermeable to solutes (concentrating segment). * **Countercurrent Multiplier:** Established by the Loop of Henle; **Countercurrent Exchanger** is the VASA RECTA. * **Clinical Correlation:** In dehydration (as seen in this patient), ADH levels rise to increase water permeability in the collecting ducts, but the PCT still performs the "heavy lifting" of bulk reabsorption.

Q: A patient is given a drug that dilates the afferent arteriole and contracts the efferent arteriole, leaving total renal vascular resistance unchanged. Which set of changes is likely to occur in the following table? (I = increased, D = decreased, NC = no change)

Table option C. ***Table option C*** - **Afferent dilation** and **efferent constriction** increases **glomerular capillary pressure**, leading to **increased GFR** while maintaining constant **RPF** since total **renal vascular resistance** remains unchanged. - **Filtration fraction** (FF = GFR/RPF) increases because GFR rises while RPF stays constant, and **glomerular capillary pressure** increases due to enhanced blood flow into and restricted flow out of glomerular capillaries. *Table option A* - This option likely shows **decreased GFR**, which contradicts the expected effect of increased **glomerular capillary pressure** from the described vascular changes. - The combination of **afferent dilation** and **efferent constriction** should enhance **filtration pressure**, not reduce it. *Table option B* - This option probably indicates **decreased filtration fraction**, which is incorrect since GFR increases more than any potential RPF changes. - **Glomerular capillary pressure** changes are likely incorrectly predicted, not accounting for the **Starling forces** modification from vascular resistance alterations. *Table option D* - This option may show **decreased glomerular capillary pressure**, which contradicts the hemodynamic effects of **afferent vasodilation** and **efferent vasoconstriction**. - The **RPF changes** are likely incorrectly predicted, not considering that total **renal vascular resistance** compensation maintains overall renal blood flow.

Question 1

In which region of the nephron are P cells (principal cells) located?

Accepted Answer

Collecting duct

Answer

Proximal Convoluted Tubule (PCT)

Answer

Loop of Henle

Answer

Distal Convoluted Tubule (DCT)

Question 2

What is the exact number of solutes transported in the thick ascending limb of the Loop of Henle per carrier pump?

Accepted Answer

Transports one Na+, one K+, and two Cl-.

Answer

Transports two Na+, two K+, and two Cl-.

Answer

Transports two Na+, one K+, and two Cl-.

Answer

Transports three Na+, two K+, and two Cl-.

Question 3

Which of the following statements is true regarding calcium reabsorption in the kidney?

Accepted Answer

The major regulating factor for calcium reabsorption is parathormone.

Answer

Most of the calcium reabsorption occurs in the distal convoluted tubule (DCT).

Answer

Parathormone decreases calcium reabsorption.

Answer

Increased plasma phosphate decreases calcium reabsorption.

Question 4

Glucose is absorbed through the apical membrane of the proximal convoluted tubule by which transporter?

Accepted Answer

SGLT-2

Answer

SGLT-1

Answer

GLUT-1

Answer

GLUT-2

Question 5

Free water clearance by the kidney is increased by which of the following?

Accepted Answer

Diabetes insipidus

Answer

Renal failure

Answer

Diuretic therapy

Answer

Diabetes mellitus

Question 6

In a cystometrogram, where does LaPlace's law have its primary application?

Accepted Answer

Phase Ib (bladder volume between 100-400 mL)

Answer

Phase Ia (bladder volume less than 100 mL)

Answer

Phase II (bladder volume more than 450 mL)

Answer

All phases of the cystometrogram

Question 7

A 20-year-old male patient presents with a decrease in urinary output to about 400ml/day. Both renal blood flow (RBF) and glomerular filtration rate (GFR) were decreased. Which of the following causes a decrease in both RBF and GFR?

Accepted Answer

Constriction of the afferent arteriole

Answer

Dilation of the efferent arteriole

Answer

Dilation of the afferent arteriole

Answer

Constriction of the efferent arteriole

Question 8

Which of the following can reduce the glomerular filtration rate (GFR)?

Accepted Answer

Endothelium-derived nitric oxide

Answer

Norepinephrine

Answer

Epinephrine

Answer

Endothelin

Question 9

A 78-year-old man presents with nausea and vomiting. On examination, he appears dehydrated, his abdomen is soft, and the jugular venous pressure is not elevated. Laboratory tests reveal hypernatremia, and his calculated free water deficit is approximately 3 L. In which part of the normal kidney is most of the water reabsorbed?

Accepted Answer

Proximal tubule

Answer

Collecting ducts

Answer

Distal tubule

Answer

Ascending loop of Henle

Question 10

A patient is given a drug that dilates the afferent arteriole and contracts the efferent arteriole, leaving total renal vascular resistance unchanged. Which set of changes is likely to occur in the following table? (I = increased, D = decreased, NC = no change)

Accepted Answer

Table option C

Answer

Table option A

Answer

Table option B

Answer

Table option D

Renal Physiology — MCQs

Renal Physiology — MCQs

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