Renal Physiology Practice Questions

Q: Which of the following substances relaxes mesangial cells in the glomerulus?

Dopamine. **Explanation:** The glomerular mesangial cells are specialized contractile cells located between the capillary loops. Their primary function is to regulate the **Glomerular Filtration Rate (GFR)** by altering the available surface area for filtration. When these cells contract, the surface area decreases (reducing GFR); when they relax, the surface area increases (raising GFR). **1. Why Dopamine is Correct:** Dopamine acts on **D1 receptors** in the kidney to cause vasodilation and **relaxation of mesangial cells**. This relaxation increases the effective filtration surface area, contributing to the increase in GFR and natriuresis (sodium excretion) typically seen with low-to-moderate dose dopamine infusions. Other substances that cause relaxation include **Atrial Natriuretic Peptide (ANP)**, cAMP, and Prostaglandin E2 (PGE2). **2. Why the Other Options are Incorrect:** * **Histamine:** Acts as a potent **contractor** of mesangial cells, thereby reducing the filtration surface area. * **Angiotensin II & III:** These are powerful vasoconstrictors. Angiotensin II is the primary hormonal regulator that causes mesangial **contraction** via AT1 receptors. Angiotensin III has similar, though less potent, effects. * **Platelet-derived growth factor (PDGF):** This is a mitogen that stimulates mesangial cell proliferation and **contraction**. It plays a significant role in the pathophysiology of many glomerular diseases (e.g., glomerulonephritis). **High-Yield Clinical Pearls for NEET-PG:** * **Contraction (Decreases GFR):** Angiotensin II, Vasopressin (ADH), Endothelin, Histamine, Noradrenaline, and PAF. * **Relaxation (Increases GFR):** Dopamine, ANP, PGE2, and cAMP. * **Mesangial Function:** They also provide structural support to capillaries and possess phagocytic properties to remove macromolecules from the basement membrane.

Q: All of the following statements concerning Atrial Natriuretic Peptide (ANP) are true EXCEPT?

Its effects are mediated by increased cyclic AMP.. **Explanation:** Atrial Natriuretic Peptide (ANP) is a powerful hormone secreted by the atrial myocytes in response to atrial stretch, serving as the body’s natural defense against fluid overload. **Why Option D is the correct answer (The Exception):** The cellular mechanism of ANP involves binding to its receptor (NPR-A), which has intrinsic **guanylyl cyclase** activity. This leads to the conversion of GTP to **cyclic GMP (cGMP)**, not cAMP. cGMP then activates protein kinase G (PKG) to mediate vasodilation and natriuresis. **Analysis of Incorrect Options:** * **Option A:** ANP is secreted in response to **increased blood volume** or pressure, which causes atrial wall stretch (mechanoreceptor activation). * **Option B:** ANP **increases GFR** through a "push-pull" mechanism: it dilates the afferent arteriole and constricts the efferent arteriole. This increases the glomerular capillary hydrostatic pressure. * **Option C:** ANP acts as an antagonist to the Renin-Angiotensin-Aldosterone System (RAAS). It **inhibits renin secretion** from juxtaglomerular cells and directly inhibits aldosterone secretion from the adrenal cortex. **High-Yield Clinical Pearls for NEET-PG:** * **Site of Action:** ANP primarily acts on the **medullary collecting ducts** to inhibit Na+ reabsorption. * **Brain Natriuretic Peptide (BNP):** Secreted by ventricles; used clinically as a marker for **Heart Failure** (high sensitivity). * **Neprilysin:** The enzyme that degrades ANP/BNP. Neprilysin inhibitors (e.g., Sacubitril) are now used in heart failure management to prolong the beneficial effects of natriuretic peptides. * **Mnemonic:** ANP = **A**fferent **N**early **P**atent (Dilates), **E**fferent **E**xtremely **E**nded (Constricts).

Q: Uremia occurs when the total GFR is reduced by approximately what percentage?

25%. **Explanation:** The correct answer is **25% (Option A)**. This question tests the understanding of the kidney's functional reserve and the progression of Chronic Kidney Disease (CKD). **1. Why 25% is correct:** The kidneys possess a massive functional reserve. Clinical symptoms of **uremia** (a syndrome caused by the accumulation of nitrogenous waste products like urea and creatinine) typically do not manifest until the total Glomerular Filtration Rate (GFR) falls below **25% of its normal value** (roughly <30 mL/min/1.73m²). At this stage, the remaining functional nephrons can no longer compensate for the loss, leading to systemic toxicity, electrolyte imbalances, and fluid overload. **2. Why the other options are incorrect:** * **50% (Option B):** When GFR is reduced by 50%, the patient is often asymptomatic. This is seen in individuals who donate a kidney; the remaining kidney undergoes compensatory hypertrophy, and the patient does not develop uremia. * **60% (Option C):** A 60% reduction (leaving 40% function) corresponds to Stage 3 CKD. While biochemical abnormalities (like mild anemia or secondary hyperparathyroidism) may begin, overt uremic symptoms are rare. * **80% (Option D):** While uremia is certainly present at an 80% reduction (leaving 20% function), the question asks for the threshold at which it *occurs*. Uremia begins to manifest earlier, around the 25% functional mark. **High-Yield Clinical Pearls for NEET-PG:** * **Stages of CKD:** Stage 1 (>90 GFR), Stage 2 (60-89), Stage 3 (30-59), Stage 4 (15-29), Stage 5 (<15 or Dialysis). * **Uremic Frost:** A late clinical sign where urea crystallizes on the skin. * **Most common cause of death in Uremia:** Cardiovascular disease (not renal failure itself). * **First sign of CKD:** Often microalbuminuria, rather than a drop in GFR.

Q: Which cells in the kidney have a secretory function?

JG cell. **Explanation:** The correct answer is **JG cell (Juxtaglomerular cell)**. **1. Why JG cells are correct:** JG cells are modified smooth muscle cells located primarily in the afferent arteriole. Their primary function is **secretory**; they synthesize, store, and release the enzyme **renin** into the bloodstream. Renin is the rate-limiting step of the Renin-Angiotensin-Aldosterone System (RAAS), which regulates blood pressure and fluid balance. These cells act as baroreceptors, sensing changes in renal perfusion pressure. **2. Analysis of incorrect options:** * **P cells (Principal cells):** Found in the collecting ducts, these cells are primarily involved in **transport (reabsorption/secretion)** rather than glandular secretion. They reabsorb sodium and water and secrete potassium under the influence of aldosterone and ADH. * **I cells (Intercalated cells):** Also found in the collecting ducts, these cells are specialized for **acid-base regulation**. Type A cells secrete $H^+$ and reabsorb $HCO_3^-$, while Type B cells do the opposite. While they "secrete" ions, they are classified as transport cells, not secretory cells in the endocrine/enzymatic sense like JG cells. * **All of the above:** This is incorrect because the term "secretory function" in renal histology specifically highlights the glandular-like production of hormones/enzymes (Renin), which is unique to the JG cells in this context. **High-Yield Clinical Pearls for NEET-PG:** * **JG Apparatus components:** JG cells (modified smooth muscle), Macula Densa (modified DCT cells acting as chemoreceptors), and Lacis cells (extraglomerular mesangial cells). * **Stimuli for Renin release:** Decreased renal perfusion (baroreceptor), decreased NaCl delivery to macula densa, and Sympathetic stimulation ($\beta_1$ receptors). * **Erythropoietin (EPO):** Another key renal "secretion," but it is produced by **peritubular interstitial fibroblasts**, not the tubular cells.

Q: In urinary system disease, gastrointestinal symptoms appear because of which of the following mechanisms?

Renogastric reflex. ### Explanation **1. Why Renogastric Reflex is Correct:** The **renogastric reflex** is a visceral autonomic reflex that explains the functional link between the kidneys and the stomach. When the kidney or ureter is irritated—most commonly due to **renal calculi (stones)** or inflammation—sensory afferent impulses are sent to the spinal cord. This triggers an inhibitory sympathetic response that decreases gastric motility and secretion. Clinically, this manifests as nausea, vomiting, and abdominal distension, which are hallmark gastrointestinal symptoms of renal colic. **2. Analysis of Incorrect Options:** * **A. Chemical reaction:** While uremia (accumulation of nitrogenous waste) in end-stage renal disease can cause "chemical" irritation of the gut lining (uremic gastritis), it is not the primary reflex mechanism for acute GI symptoms in general urinary diseases. * **C. Peritoneal reaction:** This occurs when the peritoneum is irritated (e.g., peritonitis or retroperitoneal hemorrhage). While severe renal inflammation can irritate the overlying peritoneum, it is a secondary anatomical consequence rather than the physiological mechanism governing the GI response. * **D. Reflux phenomenon:** This term usually refers to the backward flow of fluids (e.g., Vesicoureteral reflux or Gastroesophageal reflux) and does not describe a neural reflex causing multi-organ symptoms. **3. NEET-PG High-Yield Pearls:** * **Renointestinal Reflex:** Similar to the renogastric reflex, irritation of the kidney can inhibit intestinal peristalsis, leading to **paralytic ileus**. * **Nerve Supply:** The kidneys and the GI tract share common autonomic pathways (T10–L1 levels), which explains the **referred pain** and visceral cross-talk. * **Clinical Presentation:** Always consider renal stones in a patient presenting with acute "surgical abdomen" symptoms like vomiting and ileus if they also have loin pain or hematuria.

Q: Which of the following combinations correctly describes a hormone and its primary site of action within the renal tubules?

Aldosterone acting on the collecting ducts. **Explanation:** The correct answer is **A. Aldosterone acting on the collecting ducts.** **1. Why Option A is Correct:** Aldosterone is a steroid hormone secreted by the adrenal cortex. Its primary site of action is the **Principal cells (P-cells)** of the late distal tubule and, most importantly, the **collecting ducts**. It binds to mineralocorticoid receptors, leading to the upregulation of ENaC (epithelial sodium channels) and Na+/K+ ATPase pumps. This results in **sodium reabsorption** and **potassium secretion**, followed by water retention. **2. Why the Other Options are Incorrect:** * **B. Angiotensin II:** Its primary renal site of action is the **Proximal Convoluted Tubule (PCT)**, where it stimulates the Na+/H+ exchanger to increase sodium and bicarbonate reabsorption. It also acts as a potent vasoconstrictor of the efferent arteriole. * **C. Atrial Natriuretic Peptide (ANP):** ANP primarily acts on the **collecting ducts** to inhibit sodium reabsorption and on the afferent/efferent arterioles to increase GFR. It does not have a primary physiological role in the Loop of Henle. * **D. Antidiuretic Hormone (ADH/Vasopressin):** ADH acts on the **V2 receptors** in the **late distal tubule and collecting ducts** (not the PCT) to insert Aquaporin-2 channels, facilitating water reabsorption. **3. NEET-PG High-Yield Pearls:** * **PCT:** Site of maximum reabsorption (65% of filtered load). * **Thick Ascending Limb (TAL):** Site of action for Loop Diuretics (inhibits Na+-K+-2Cl- cotransporter). * **Early Distal Tubule:** Site of action for Thiazide diuretics (inhibits Na+-Cl- cotransporter). * **Liddle’s Syndrome:** A clinical condition involving overactive ENaC channels in the collecting duct, mimicking hyperaldosteronism.

Question 1

Which of the following is a non-osmotic stimulus for ADH secretion?

Accepted Answer

Hemorrhage

Answer

Uremia

Answer

Hyperglycemia

Answer

Excessive water ingestion

Question 2

Liddle syndrome is caused by a genetic defect in which of the following?

Accepted Answer

ENaC (epithelial sodium channel) in the collecting duct/tubule

Answer

Na-K-2Cl co-transporter in the thick ascending limb of the loop of Henle

Answer

Na-Cl cotransporter in the distal tubule

Answer

Aquaporin 2 (AQP2) channel in the collecting duct

Question 3

Which of the following substances relaxes mesangial cells in the glomerulus?

Accepted Answer

Dopamine

Answer

Histamine

Answer

Angiotensin III

Answer

Platelet-derived growth factor (PDGF)

Question 4

All of the following statements concerning Atrial Natriuretic Peptide (ANP) are true EXCEPT?

Accepted Answer

Its effects are mediated by increased cyclic AMP.

Answer

Its secretion is increased by an increase in blood volume.

Answer

It increases glomerular filtration rate.

Answer

It inhibits renin secretion.

Question 5

Uremia occurs when the total GFR is reduced by approximately what percentage?

Accepted Answer

25%

Answer

50%

Answer

60%

Answer

80%

Question 6

Genetic expression of Na-K-ATPase is induced by which of the following?

Accepted Answer

Aldosterone

Answer

Cortisol

Answer

Thyroxine

Answer

ACTH

Question 7

In urinary system disease, gastrointestinal symptoms appear due to which phenomenon?

Accepted Answer

Renogastric reflex

Answer

Chemical reactions

Answer

Peritoneal reactions

Answer

Reflux phenomenon

Question 8

Which cells in the kidney have a secretory function?

Accepted Answer

JG cell

Answer

I cell

Answer

P cell

Answer

All of the above

Question 9

In urinary system disease, gastrointestinal symptoms appear because of which of the following mechanisms?

Accepted Answer

Renogastric reflex

Answer

Chemical reaction

Answer

Peritoneal reaction

Answer

Reflux phenomenon

Question 10

Which of the following combinations correctly describes a hormone and its primary site of action within the renal tubules?

Accepted Answer

Aldosterone acting on the collecting ducts

Answer

Angiotensin acting on the distal tubule

Answer

Atrial Natriuretic Peptide (ANP) acting on the loop of Henle

Answer

Antidiuretic Hormone (ADH) acting on the proximal tubule

Renal Physiology — MCQs

Renal Physiology — MCQs

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