Renal Physiology Practice Questions

Q: Which cells are responsible for acid secretion in the kidney?

I cells. **Explanation:** The correct answer is **I cells (Intercalated cells)**. These cells are located in the late distal tubule and the collecting duct and play a vital role in acid-base balance. 1. **Why I cells are correct:** There are two types of Intercalated cells: * **Type A (Alpha) cells:** Responsible for **acid secretion**. They utilize H⁺-ATPase and H⁺/K⁺-ATPase pumps on their apical membrane to secrete hydrogen ions into the tubular lumen while reabsorbing bicarbonate (HCO₃⁻) via the basolateral Cl⁻/HCO₃⁻ exchanger (Anion Exchanger 1). * **Type B (Beta) cells:** Responsible for **bicarbonate secretion** (active during alkalosis). 2. **Why other options are incorrect:** * **P cells (Principal cells):** These are the most abundant cells in the collecting duct. Their primary function is **sodium reabsorption** (via ENaC channels) and **potassium secretion**, regulated by Aldosterone. They also reabsorb water via Aquaporin-2 under the influence of ADH. * **Mesangial cells:** These are specialized smooth-muscle-like cells located in the glomerulus. They provide structural support, regulate the glomerular filtration rate (GFR) through contraction, and have phagocytic properties. * **Pericytes:** In the kidney, pericytes are found around the vasa recta. They regulate medullary blood flow and are the primary source of **Erythropoietin (EPO)** production. **High-Yield Clinical Pearls for NEET-PG:** * **Type 1 Renal Tubular Acidosis (Distal RTA):** Caused by a failure of Type A Intercalated cells to secrete H⁺, leading to a high urinary pH (>5.5). * **Aldosterone's dual action:** It acts on P cells to reabsorb Na⁺ and on Type A I-cells to stimulate H⁺ secretion. This is why hyperaldosteronism leads to metabolic alkalosis. * **Memory Aid:** **A**lpha cells secrete **A**cid; **B**eta cells secrete **B**ase (Bicarbonate).

Q: Alpha-adrenergic receptors are located in which part of the urinary bladder?

Base of bladder. The innervation of the urinary bladder is a high-yield topic in renal physiology, governed by the principle of "reciprocal innervation" between the detrusor muscle and the internal urethral sphincter. ### **Explanation of the Correct Answer** The **base of the bladder** (including the bladder neck and the internal urethral sphincter) is rich in **Alpha-1 ($\alpha_1$) adrenergic receptors**. * **Mechanism:** Stimulation of these receptors by the sympathetic nervous system (via the Hypogastric nerve, T11-L2) causes **contraction** of the internal sphincter. * **Function:** This action promotes urinary storage by increasing outlet resistance and preventing the voiding of urine during the filling phase. ### **Analysis of Incorrect Options** * **A. Dome of bladder:** The dome and body of the bladder consist primarily of the detrusor muscle. This area is dominated by **Beta-3 ($\beta_3$) adrenergic receptors**, which cause muscle relaxation to allow for bladder filling, and **Muscarinic (M3) receptors**, which cause contraction during micturition. * **C & D:** These are incorrect because the distribution of adrenergic receptors is anatomically distinct to ensure coordinated storage and voiding. ### **High-Yield Clinical Pearls for NEET-PG** 1. **Pharmacology Link:** Alpha-blockers (e.g., **Tamsulosin**) are used in Benign Prostatic Hyperplasia (BPH) to relax the bladder neck (base) and improve urine flow. 2. **Sympathetic vs. Parasympathetic:** * **Sympathetic (Hypogastric N.):** "Fills" the bladder (Relaxes detrusor via $\beta_3$, contracts sphincter via $\alpha_1$). * **Parasympathetic (Pelvic N.):** "Empties" the bladder (Contracts detrusor via $M_3$). 3. **Somatic Control:** The external urethral sphincter is under voluntary control via the **Pudendal nerve** (S2-S4) acting on Nicotinic receptors.

Q: A patient has a GFR of 100 ml/min, her urine flow rate is 2.0 ml/min, and her plasma glucose concentration is 200 mg/100 ml. If the kidney transport maximum for glucose is 250 mg/min, what would be her approximate rate of glucose excretion?

0 mg/min. To solve this problem, we must compare the **Filtered Load** of glucose with the **Transport Maximum ($T_m$)**. ### 1. Calculation of Filtered Load The filtered load is the amount of glucose that enters the Bowman’s capsule per minute. * **Formula:** Filtered Load = GFR × Plasma Concentration ($P_x$) * **Given:** GFR = 100 ml/min; $P_x$ = 200 mg/100 ml (which is 2 mg/ml). * **Calculation:** $100 \text{ ml/min} \times 2 \text{ mg/ml} = \mathbf{200 \text{ mg/min}}$. ### 2. Comparison with Transport Maximum ($T_m$) The $T_m$ is the maximum rate at which the proximal tubule can reabsorb glucose via SGLT transporters. * **Given:** $T_m = 250 \text{ mg/min}$. * **Logic:** Since the Filtered Load (200 mg/min) is **less than** the $T_m$ (250 mg/min), the kidneys have the capacity to reabsorb 100% of the filtered glucose. * **Excretion:** Excretion = Filtered Load – Reabsorption. Here, $200 - 200 = \mathbf{0 \text{ mg/min}}$. --- ### Why Incorrect Options are Wrong: * **B, C, and D:** These values assume that the $T_m$ has been exceeded. If the filtered load were, for example, 350 mg/min, the excretion would be $350 - 250 = 100 \text{ mg/min}$. In this case, however, the reabsorptive capacity is sufficient to ensure no glucose is lost in the urine. --- ### High-Yield Clinical Pearls for NEET-PG: * **Renal Threshold for Glucose:** This is the plasma concentration at which glucose first appears in the urine (glycosuria). It is typically **180 mg/dL**. * **Splay Phenomenon:** The renal threshold is lower than the $T_m$ would predict due to the "splay" phenomenon, caused by the heterogeneity of nephrons and the low affinity of SGLT transporters near saturation. * **Transporters:** Glucose is reabsorbed in the PCT via **SGLT-2** (early PCT, high capacity) and **SGLT-1** (late PCT, high affinity). SGLT-2 inhibitors (e.g., Dapagliflozin) are now key drugs in managing Diabetes and Heart Failure.

Q: Maximum potassium reabsorption occurs in which part of the nephron?

Proximal convoluted tubule. **Explanation:** The handling of potassium ($K^+$) by the kidney is unique because it involves both reabsorption and secretion. However, the vast majority of filtered potassium is reabsorbed in the early segments of the nephron, regardless of the body's potassium status. **1. Why Proximal Convoluted Tubule (PCT) is correct:** The **PCT is the primary site of potassium reabsorption**, accounting for approximately **65-70%** of the filtered load. This process is primarily passive and occurs via the **paracellular route**. It is driven by solvent drag (as water is reabsorbed) and the positive transtubular potential that develops in the late PCT. An additional 25-30% is reabsorbed in the Thick Ascending Limb (TAL) via the Na-K-2Cl cotransporter. **2. Why the other options are incorrect:** * **Distal Convoluted Tubule (DCT) & Collecting Ducts:** These segments are responsible for the **fine-tuning** of potassium balance. While some reabsorption can occur here via α-intercalated cells (using H-K ATPase) during potassium depletion, these segments are more clinically significant for **potassium secretion**. * **Cortical Collecting Duct:** This is the major site of **potassium secretion** regulated by Aldosterone. Principal cells secrete $K^+$ into the tubular lumen to maintain systemic balance. **3. High-Yield Clinical Pearls for NEET-PG:** * **Fixed vs. Variable:** $K^+$ reabsorption in the PCT and Loop of Henle is "fixed" (constant), whereas secretion in the late distal tubule/collecting duct is "variable" and regulated by dietary intake and hormones. * **Aldosterone Effect:** Aldosterone acts on the Principal cells of the collecting duct to increase $Na^+$ reabsorption and $K^+$ secretion. * **Diuretics:** Loop diuretics and Thiazides increase $K^+$ delivery to the distal nephron, leading to increased $K^+$ secretion and subsequent hypokalemia.

Q: Which of the following helps to create a high medullary osmotic gradient?

Thick ascending loop of Henle. The medullary osmotic gradient is essential for the kidney's ability to concentrate urine. Understanding the distinction between **creating** (establishing) and **maintaining** this gradient is high-yield for NEET-PG. ### 1. Why Option A is Correct The **Thick Ascending Limb (TAL)** of the Loop of Henle is the **"Single Effect"** or the "Engine" of the counter-current system. It actively transports Na⁺, K⁺, and 2Cl⁻ (via the NKCC2 transporter) from the tubular lumen into the medullary interstitium. Because the TAL is **impermeable to water**, it increases the osmolarity of the interstitium without water following the solutes. This active process is the primary step that **creates** the hypertonic medullary gradient. ### 2. Why Other Options are Incorrect * **Vasa Recta (Option B):** These vessels act as **Counter-current Exchangers**. They do not create the gradient; they **maintain** it by removing excess water and reabsorbing solutes in a way that prevents the "washout" of the medullary hypertonicity. * **Counter-current Exchanger System (Option C):** This refers specifically to the passive exchange mechanism (primarily in the vasa recta). While it is vital for preserving the gradient, it is a passive process and cannot establish the gradient from scratch. * **Option D:** Incorrect because only the active "multiplier" (TAL) creates the gradient. ### 3. High-Yield Clinical Pearls * **Counter-current Multiplier:** Refers to the Loop of Henle (creates the gradient). * **Counter-current Exchanger:** Refers to the Vasa Recta (maintains the gradient). * **Urea Recycling:** Contributes nearly 50% of the medullary osmotic gradient, particularly in the inner medulla. * **Loop Diuretics (e.g., Furosemide):** Act by inhibiting the NKCC2 transporter in the TAL, thereby "washing out" the medullary gradient and preventing urine concentration.

Q: Which of the following hormones is not secreted by the kidney?

Angiotensin I. ### Explanation The kidney is a vital endocrine organ, but it does not directly secrete **Angiotensin I**. **Why Angiotensin I is the correct answer:** Angiotensin I is not secreted by any gland; rather, it is **formed in the plasma**. The process begins when the kidneys secrete the enzyme **Renin** into the bloodstream. Renin then acts on **Angiotensinogen** (a plasma protein synthesized by the **liver**) to cleave it into Angiotensin I. Subsequently, Angiotensin I is converted to Angiotensin II by the Angiotensin-Converting Enzyme (ACE), primarily in the lungs. **Why the other options are incorrect:** * **1,25-dihydroxycholecalciferol (Calcitriol):** This is the active form of Vitamin D. The final step of its activation (hydroxylation of 25-hydroxyvitamin D) occurs in the **proximal convoluted tubules** of the kidney via the enzyme 1-alpha-hydroxylase. * **Renin:** Produced and secreted by the **Juxtaglomerular (JG) cells** of the afferent arteriole in response to low blood pressure or low sodium delivery. * **Erythropoietin (EPO):** Approximately 85-90% of EPO is secreted by the **interstitial cells of the peritubular capillary bed** in the renal cortex in response to hypoxia. **High-Yield Clinical Pearls for NEET-PG:** * **Site of EPO production:** In adults, it is the kidney; in the fetus, it is primarily the **liver**. * **Thrombopoietin:** While mainly produced in the liver, the kidney also produces a small amount. * **Prostaglandins:** The kidney also secretes PGE2 and PGI2, which act as local vasodilators to maintain renal blood flow.

Question 1

A freely filterable substance that is neither reabsorbed nor secreted has a renal artery concentration of 12 mg/mL and a renal vein concentration of 9 mg/mL. Which of the following is the filtration fraction?

Accepted Answer

0.25

Answer

0.05

Answer

0.15

Answer

0.35

Question 2

Which mechanism does NOT contribute to the countercurrent multiplier in the nephron?

Accepted Answer

Sodium reabsorption out of the thin descending limb of the loop of Henle

Answer

Active transport of sodium and chloride out of the thick ascending limb of the loop of Henle

Answer

Water reabsorption in the thin descending limb of the loop of Henle

Answer

Urea concentration in the collecting duct

Question 3

Which cells are responsible for acid secretion in the kidney?

Accepted Answer

I cells

Answer

P cells

Answer

Mesangial cells

Answer

Pericytes

Question 4

Alpha-adrenergic receptors are located in which part of the urinary bladder?

Accepted Answer

Base of bladder

Answer

Dome of bladder

Answer

Both of above

Answer

None of above

Question 5

A patient has a GFR of 100 ml/min, her urine flow rate is 2.0 ml/min, and her plasma glucose concentration is 200 mg/100 ml. If the kidney transport maximum for glucose is 250 mg/min, what would be her approximate rate of glucose excretion?

Accepted Answer

0 mg/min

Answer

50 mg/min

Answer

100 mg/min

Answer

150 mg/min

Question 6

Maximum potassium reabsorption occurs in which part of the nephron?

Accepted Answer

Proximal convoluted tubule

Answer

Distal convoluted tubule

Answer

Cortical collecting duct

Answer

Medullary collecting duct

Question 7

Which of the following helps to create a high medullary osmotic gradient?

Accepted Answer

Thick ascending loop of Henle

Answer

Vasa recta

Answer

Counter-current exchanger system

Answer

All of the above

Question 8

All regulation of renal potassium excretion and total body potassium balance occurs in which part of the nephron?

Accepted Answer

Collecting duct

Answer

Proximal convoluted tubule

Answer

Ascending loop of Henle

Answer

Descending loop of Henle

Question 9

Which of the following is NOT a function of angiotensin?

Accepted Answer

Acts on the adrenal medulla and stimulates steroidogenesis

Answer

Stimulates aldosterone secretion from the adrenal cortex

Answer

Increases renal blood flow (RBF)

Answer

Directly causes vasoconstriction

Question 10

Which of the following hormones is not secreted by the kidney?

Accepted Answer

Angiotensin I

Answer

1,25-dihydroxycholecalciferol

Answer

Renin

Answer

Erythropoietin

Renal Physiology — MCQs

Renal Physiology — MCQs

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