Renal Physiology Practice Questions

Q: Non-oliguric renal failure is caused by damage to which part of the nephron?

Collecting duct. **Explanation:** **1. Why the Collecting Duct is Correct:** Non-oliguric renal failure (NORF) is a clinical state where the kidneys fail to concentrate urine despite a decrease in the Glomerular Filtration Rate (GFR). The **Collecting Duct (CD)** is the primary site for final urine concentration under the influence of Antidiuretic Hormone (ADH). Damage to the collecting duct cells (often due to nephrotoxins like aminoglycosides or partial obstruction) results in a loss of responsiveness to ADH. Consequently, the kidney cannot reabsorb water, leading to a high output of dilute urine (polyuria or normal volume) despite failing excretory functions. **2. Why the Other Options are Incorrect:** * **Afferent & Efferent Arterioles (A & B):** Damage to these vessels primarily affects the GFR and renal blood flow. Significant damage here usually leads to **oliguric** renal failure because the initial filtration pressure drops sharply, reducing urine formation at the source. * **Ascending Limb of the Loop of Henle (C):** While this segment is crucial for the countercurrent multiplier system, damage here typically presents as specific electrolyte wasting (like Bartter-like syndromes). While it affects concentration, the definitive "non-oliguric" failure pattern is most classically associated with distal tubular and collecting duct dysfunction. **3. NEET-PG High-Yield Pearls:** * **Definition:** Non-oliguric renal failure is defined as acute kidney injury (AKI) with a urine output **>400 ml/day**. * **Common Causes:** Aminoglycoside toxicity (e.g., Gentamicin), Amphotericin B, and contrast-induced nephropathy are classic triggers for non-oliguric AKI. * **Prognosis:** Non-oliguric AKI generally has a **better prognosis** and lower mortality rate compared to oliguric AKI. * **Key Concept:** In NORF, the "quality" of filtration is lost (waste retention) even if the "quantity" of urine remains normal.

Q: Which of the following is not a part of the glomerular filtration barrier?

Mesangial cell. The **glomerular filtration barrier (GFB)** is a highly specialized three-layered structure responsible for the ultrafiltration of blood while preventing the passage of plasma proteins. ### Why Mesangial Cells are the Correct Answer **Mesangial cells** are located between the glomerular capillaries but are **not** part of the filtration interface itself. Their primary functions include providing structural support to the capillary loops, secreting the extracellular matrix, and performing phagocytosis to remove trapped macromolecules. While they can influence the glomerular filtration rate (GFR) by contracting in response to Angiotensin II (thereby reducing surface area), they do not form a layer of the barrier through which filtrate must pass. ### Analysis of Incorrect Options (Components of the GFB) 1. **Endothelial cells (Option B):** The innermost layer. These are **fenestrated** capillaries (pores of 70–100 nm) that prevent the passage of blood cells but allow most plasma components through. 2. **Basement membrane (Option D):** The middle layer. It is composed of Type IV collagen and heparan sulfate proteoglycans. It acts as a **size and charge barrier** (negatively charged), repelling proteins like albumin. 3. **Podocytes (Option C):** The outermost layer (visceral epithelium). They possess foot processes (pedicels) that interdigitate to form **filtration slits** bridged by a diaphragm containing the protein **nephrin**. ### High-Yield Clinical Pearls for NEET-PG * **Charge Selectivity:** The GFB is negatively charged due to sialoglycoproteins and heparan sulfate. Loss of this negative charge (e.g., in **Minimal Change Disease**) leads to selective albuminuria. * **Nephrin:** Mutations in the gene encoding nephrin (*NPHS1*) result in **Finnish-type congenital nephrotic syndrome**. * **Goodpasture Syndrome:** Characterized by antibodies against the alpha-3 chain of Type IV collagen in the glomerular basement membrane.

Q: Which of the following ions is least absorbed in the renal tubules?

Creatinine. **Explanation:** The renal handling of substances depends on the balance between filtration, reabsorption, and secretion. The correct answer is **Creatinine** because it is the only substance among the options that undergoes **zero reabsorption** in the renal tubules. **1. Why Creatinine is Correct:** Creatinine is a metabolic byproduct of muscle metabolism. Once filtered at the glomerulus, it is **not reabsorbed** by the tubules. In fact, a small amount is actively secreted into the lumen. Because the amount excreted in urine is slightly more than the amount filtered, creatinine clearance is used as a clinical marker to estimate the Glomerular Filtration Rate (GFR). **2. Why the Other Options are Incorrect:** * **Sodium (A):** Sodium is the most actively reabsorbed ion. Approximately **99%** of filtered sodium is reabsorbed throughout the nephron (65% in the proximal tubule) to maintain fluid and electrolyte balance. * **Urea (B):** Urea is a waste product, but it is still partially reabsorbed. About **40-50%** of filtered urea is reabsorbed passively, primarily in the proximal tubule and medullary collecting ducts (where it contributes to the medullary osmotic gradient). * **Glucose (D):** Under normal physiological conditions, **100%** of filtered glucose is reabsorbed in the Proximal Convoluted Tubule (PCT) via SGLT2 and SGLT1 transporters. It only appears in urine if the blood glucose level exceeds the renal threshold (~180 mg/dL). **High-Yield Clinical Pearls for NEET-PG:** * **Inulin:** The "gold standard" for GFR measurement because it is freely filtered and undergoes **neither reabsorption nor secretion**. * **PAH (Para-aminohippurate):** Used to measure Renal Plasma Flow (RPF) because it is filtered and almost entirely secreted, resulting in near-total clearance. * **Renal Threshold for Glucose:** 180 mg/dL; **Transport Maximum (TmG):** 375 mg/min in men, 300 mg/min in women.

Q: In the absence of vasopressin, what is the greatest fraction of filtered water absorbed?

Proximal tubule.. **Explanation:** The correct answer is **Proximal tubule (A)**. The absorption of water in the nephron is divided into two types: **obligatory** and **facultative**. 1. **Proximal Convoluted Tubule (PCT):** Approximately **65-70%** of filtered water is reabsorbed here regardless of the body's hydration status or the presence of Antidiuretic Hormone (ADH/Vasopressin). This is "obligatory" water reabsorption, driven by the active transport of sodium (iso-osmotic reabsorption). Even in the complete absence of vasopressin (e.g., Diabetes Insipidus), the PCT remains the site where the largest fraction of water is reclaimed. **Why other options are incorrect:** * **Loop of Henle (B):** Reabsorbs about 15% of filtered water, primarily in the thin descending limb. The ascending limb is impermeable to water. * **Distal Tubule (C) & Cortical Collecting Duct (D):** These segments are responsible for "facultative" water reabsorption. Their permeability to water is strictly dependent on **Vasopressin (ADH)** acting on V2 receptors to insert Aquaporin-2 channels. In the absence of vasopressin, these segments become virtually impermeable to water, leading to the excretion of large volumes of dilute urine. **High-Yield Clinical Pearls for NEET-PG:** * **Obligatory Water Reabsorption:** Occurs in the PCT (65%) and Descending Loop of Henle (15%). Total = ~80%. * **Facultative Water Reabsorption:** Occurs in the Late DT and Collecting Ducts (remaining ~20%) under ADH control. * **Descending Limb of Henle:** Permeable to water but impermeable to solutes (concentrating segment). * **Ascending Limb of Henle:** Impermeable to water but active in solute reabsorption (diluting segment). * **Maximum Urine Osmolality:** 1200–1400 mOsm/L (in the presence of ADH). * **Minimum Urine Osmolality:** 30–50 mOsm/L (in the absence of ADH).

Q: The neonatal kidney achieves concentrating ability equivalent to the adult kidney by what age?

One year of age. **Explanation:** The neonatal kidney is anatomically complete at birth (nephrogenesis ends at 34-36 weeks of gestation), but it is functionally immature. The ability to concentrate urine depends on the **medullary osmotic gradient** and the responsiveness of the distal tubules to **Antidiuretic Hormone (ADH)**. **1. Why Option A is Correct:** While glomerular filtration rate (GFR) increases rapidly after birth, the concentrating capacity matures more slowly. At birth, a neonate can only concentrate urine to approximately 500–700 mOsm/L. This limitation is due to shorter Loops of Henle, lower urea concentration in the medulla, and relative insensitivity to ADH. By **one year of age**, the tubular function and medullary gradient mature sufficiently to reach the adult concentrating capacity of approximately **1200–1400 mOsm/L**. **2. Why Other Options are Incorrect:** * **Option B:** By 18 months, renal function is well-established, but the specific physiological milestone for adult-level concentration is typically reached by the first birthday. * **Option C:** At 3 to 6 months, GFR and some tubular functions are improving, but the kidney still cannot handle high solute loads as effectively as an adult kidney. * **Option D:** Puberty is far too late; most renal parameters (GFR, secretion, and concentration) reach adult levels between 1 and 2 years of age. **High-Yield Clinical Pearls for NEET-PG:** * **GFR Milestone:** GFR reaches adult levels (adjusted for body surface area) by **2 years of age**. * **Neonatal Vulnerability:** Because neonates cannot concentrate urine effectively, they are at a much higher risk of **dehydration** and hypernatremia during periods of fluid loss (e.g., diarrhea). * **Urea’s Role:** The lower concentrating ability in infants is partly due to their high anabolic state; they use dietary protein for growth, leaving less urea available to contribute to the medullary osmotic gradient.

Q: What is the primary function of vasopressin?

Water absorption in the collecting duct. ### Explanation **Correct Answer: C. Water absorption in the collecting duct** **Mechanism:** Vasopressin, also known as **Antidiuretic Hormone (ADH)**, is synthesized in the hypothalamus (supraoptic and paraventricular nuclei) and released from the posterior pituitary. Its primary action is to maintain water homeostasis. It acts on the **V2 receptors** located on the basolateral membrane of the **principal cells** in the **Late Distal Tubule and Collecting Ducts**. This triggers a cAMP-mediated signaling pathway that leads to the insertion of **Aquaporin-2 (AQP2)** water channels into the apical membrane. This increases the permeability of the collecting duct, allowing water to be reabsorbed back into the medullary interstitium via an osmotic gradient. **Why other options are incorrect:** * **Option A & D:** The **Proximal Convoluted Tubule (PCT)** is responsible for the bulk reabsorption (65%) of water and solutes (like Sodium). However, water reabsorption in the PCT is "obligatory" (follows solutes) and is **independent of ADH**. * **Option B:** The **Loop of Henle** (specifically the descending limb) is permeable to water, but this is driven by the countercurrent multiplier system, not by vasopressin. Vasopressin does, however, increase urea recycling in the medullary collecting duct to maintain this gradient. **High-Yield NEET-PG Pearls:** * **V1 Receptors:** Located on vascular smooth muscle; cause vasoconstriction (hence the name "Vasopressin"). * **Diabetes Insipidus (DI):** Deficiency of ADH (Central DI) or resistance to ADH (Nephrogenic DI) leads to polyuria and dilute urine. * **SIADH:** Excessive ADH secretion leads to water retention and **euvolemic hyponatremia**. * **Urea Transport:** ADH also increases the activity of **UT-A1 urea transporters** in the inner medullary collecting duct, contributing to the corticomedullary osmotic gradient.

Question 1

Non-oliguric renal failure is caused by damage to which part of the nephron?

Accepted Answer

Collecting duct

Answer

Afferent arteriole

Answer

Efferent arteriole

Answer

Ascending limb of the Loop of Henle

Question 2

Which of the following is not a part of the glomerular filtration barrier?

Accepted Answer

Mesangial cell

Answer

Endothelial cell

Answer

Podocyte

Answer

Basement membrane

Question 3

Which of the following ions is least absorbed in the renal tubules?

Accepted Answer

Creatinine

Answer

Sodium

Answer

Urea

Answer

Glucose

Question 4

In the absence of vasopressin, what is the greatest fraction of filtered water absorbed?

Accepted Answer

Proximal tubule.

Answer

Loop of Henle.

Answer

Distal tubule.

Answer

Cortical collecting duct.

Question 5

Glomerular filtration rate (GFR) is determined by?

Accepted Answer

All of the above

Answer

Afferent arteriolar resistance

Answer

Efferent arteriolar resistance

Answer

Mean arterial pressure

Question 6

Impaired function of aquaporins results in which of the following conditions?

Accepted Answer

Nephrogenic diabetes insipidus

Answer

Liddle syndrome

Answer

Cystic fibrosis

Answer

Baer syndrome

Question 7

The neonatal kidney achieves concentrating ability equivalent to the adult kidney by what age?

Accepted Answer

One year of age

Answer

Eighteen months of age

Answer

Three to six months of age

Answer

Just before puberty

Question 8

Acute metabolic acidosis tends to _____ intracellular K+ concentration and _____ K+ secretion by the cortical collecting tubules?

Accepted Answer

Decrease, decrease

Answer

Increase, increase

Answer

Increase, decrease

Answer

Decrease, increase

Question 9

Activation of the renin stimulates which of the following?

Accepted Answer

Sodium retention

Answer

Water excretion

Answer

Potassium retention

Answer

Magnesium excretion

Question 10

What is the primary function of vasopressin?

Accepted Answer

Water absorption in the collecting duct

Answer

Water absorption in the proximal convoluted tubule (PCT)

Answer

Water absorption in the loop of Henle

Answer

Sodium (Na+) absorption in the PCT

Renal Physiology — MCQs

Renal Physiology — MCQs

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