Renal Physiology Practice Questions

Q: What is the normal glomerular capillary pressure?

45 mmHg. **Explanation:** The glomerular capillary pressure ($P_{GC}$) is the primary driving force for glomerular filtration. In a healthy adult, this pressure is approximately **45 mmHg** (ranging between 45–50 mmHg in modern physiological texts like Boron & Boulpaep, though older texts may cite 60 mmHg). **Why 45 mmHg is correct:** Unlike systemic capillaries where pressure drops significantly, the glomerular capillaries maintain a high and relatively constant pressure. This is due to the unique "portal-like" arrangement where the capillaries are situated between two high-resistance vessels: the **afferent and efferent arterioles**. The high resistance of the efferent arteriole creates a "back-up" of blood, ensuring $P_{GC}$ remains high enough to favor continuous filtration across the entire length of the capillary. **Analysis of Incorrect Options:** * **15 mmHg (A):** This value is closer to the **Bowman’s space hydrostatic pressure** ($P_{BS}$), which opposes filtration. * **25 mmHg (B):** This represents the **Glomerular capillary oncotic pressure** ($\pi_{GC}$) at the afferent end, which also opposes filtration. * **35 mmHg (C):** This is the typical pressure in systemic capillaries at the arterial end; it is insufficient for the high-demand filtration required by the kidneys. **High-Yield NEET-PG Pearls:** 1. **Net Filtration Pressure (NFP):** Calculated as $P_{GC} - (P_{BS} + \pi_{GC})$. Using standard values: $45 - (15 + 20) = 10 \text{ mmHg}$. 2. **Autoregulation:** Myogenic mechanisms and Tubuloglomerular Feedback (TGF) maintain $P_{GC}$ constant despite fluctuations in mean arterial pressure (80–170 mmHg). 3. **Effect of Arterioles:** Constriction of the **efferent** arteriole increases $P_{GC}$ and GFR, while constriction of the **afferent** arteriole decreases both.

Q: What percentage of filtered glucose is reabsorbed in the late proximal convoluted tubule?

90-95%. **Explanation:** In a healthy individual, 100% of filtered glucose is reabsorbed in the **Proximal Convoluted Tubule (PCT)**, ensuring that no glucose appears in the urine. This process occurs via secondary active transport in two distinct segments: 1. **Early PCT (S1 Segment):** This is the primary site of glucose reabsorption. High-capacity, low-affinity **SGLT-2** transporters (coupled with GLUT-2) reabsorb approximately **90–95%** of the filtered glucose load. 2. **Late PCT (S2/S3 Segments):** The remaining **5–10%** of glucose is "mopped up" by low-capacity, high-affinity **SGLT-1** transporters (coupled with GLUT-1). **Analysis of Options:** * **Option A (90-95%):** Correct. This represents the bulk of glucose reabsorption occurring in the early segments of the PCT via SGLT-2. * **Option B, C, and D:** These are incorrect as they significantly underestimate the efficiency of the proximal tubule. By the time the filtrate leaves the PCT, glucose concentration is effectively zero. **High-Yield Clinical Pearls for NEET-PG:** * **Renal Threshold for Glucose:** Glucose starts appearing in urine (glycosuria) when blood glucose levels exceed **180 mg/dL**. * **Transport Maximum ($T_m$):** The point at which all transporters are saturated; for men, it is approximately **375 mg/min**. * **SGLT-2 Inhibitors (e.g., Dapagliflozin):** A modern class of anti-diabetic drugs that work by inhibiting the 90-95% reabsorption in the early PCT, promoting glucose excretion. * **Fanconi Syndrome:** A generalized dysfunction of the PCT leading to glycosuria despite normal blood glucose levels.

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: What is the normal glomerular filtration rate?

125 ml/min. **Explanation:** The **Glomerular Filtration Rate (GFR)** is the volume of fluid filtered from the glomerular capillaries into the Bowman’s capsule per unit of time. In a healthy, average-sized adult (70 kg), the standard GFR is approximately **125 ml/min** (or 180 Liters per day). **Why Option B is correct:** The GFR is determined by the balance of Starling forces (hydrostatic and oncotic pressures) across the glomerular membrane and the capillary filtration coefficient ($K_f$). Under physiological conditions, the net filtration pressure results in a clearance of 125 ml/min. This value represents about 20% of the total renal plasma flow (Renal Plasma Flow $\approx$ 600-650 ml/min), a ratio known as the **Filtration Fraction**. **Why other options are incorrect:** * **Option A (100 ml/min):** While this value may be seen in early stages of chronic kidney disease (CKD) or in smaller individuals, it is below the standard physiological average for a healthy adult. * **Options C & D (150–175 ml/min):** These values represent states of hyperfiltration. While GFR can increase during pregnancy (due to increased cardiac output and renal blood flow), these are not considered the "normal" baseline values for the general population. **High-Yield Clinical Pearls for NEET-PG:** * **Gold Standard Marker:** **Inulin** clearance is the gold standard for measuring GFR because it is freely filtered but neither reabsorbed nor secreted. * **Clinical Marker:** **Creatinine** clearance is the most common clinical method used, though it slightly overestimates GFR because a small amount is secreted by the tubules. * **Filtration Fraction (FF):** $FF = GFR / RPF$. Normal FF is **0.2 (20%)**. * **Autoregulation:** GFR remains constant between a Mean Arterial Pressure (MAP) of **75 to 160 mmHg** due to myogenic mechanisms and tubuloglomerular feedback.

Question 1

The kidney normally does NOT allow transglomerular passage of which of the following substances?

Accepted Answer

B-2 microglobulin

Answer

Lysozyme

Answer

Myoglobin

Answer

Immunoglobulin

Question 2

The independence of renal blood flow from mean systemic arterial pressure is termed:

Accepted Answer

Autoregulation

Answer

Glomerulo-tubular balance

Answer

Distal tubule-glomerular feedback

Answer

Flow dependence of renal oxygen consumption

Question 3

What is the normal glomerular capillary pressure?

Accepted Answer

45 mmHg

Answer

15 mmHg

Answer

25 mmHg

Answer

35 mmHg

Question 4

What percentage of filtered glucose is reabsorbed in the late proximal convoluted tubule?

Accepted Answer

90-95%

Answer

50-60%

Answer

20-30%

Answer

5-10%

Question 5

Which cells are responsible for acid secretion in the kidney?

Accepted Answer

I cells

Answer

P cells

Answer

Mesangial cells

Answer

Pericytes

Question 6

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 7

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 8

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 9

What is the normal glomerular filtration rate?

Accepted Answer

125 ml/min

Answer

100 ml/min

Answer

150 ml/min

Answer

175 ml/min

Question 10

At what level of the nephron is isotonic urine formed?

Accepted Answer

Distal Convoluted Tubule (DCT)

Answer

Proximal Convoluted Tubule (PCT)

Answer

Ascending limb of the Loop of Henle

Answer

Descending limb of the Loop of Henle

Renal Physiology — MCQs

Renal Physiology — MCQs

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