Renal Physiology Practice Questions

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.

Q: If the renal plasma flow (RPF) is 600 mL/min and the hematocrit (hct) is 45%, what is the renal blood flow?

1090 mL/min. ### Explanation **1. Understanding the Correct Answer (Option B: 1090 mL/min)** Renal Blood Flow (RBF) represents the total volume of blood delivered to the kidneys per unit time. Blood consists of two main components: **Plasma** and **Formed Elements (primarily RBCs)**. The Hematocrit (Hct) represents the fraction of blood occupied by cells. Therefore, the remaining fraction $(1 - \text{Hct})$ represents the Plasma. The mathematical relationship is: $$\text{RBF} = \frac{\text{Renal Plasma Flow (RPF)}}{1 - \text{Hematocrit}}$$ **Calculation:** * RPF = 600 mL/min * Hct = 45% (0.45) * Plasma fraction = $1 - 0.45 = 0.55$ * $\text{RBF} = \frac{600}{0.55} \approx \mathbf{1090.9 \text{ mL/min}}$ **2. Analysis of Incorrect Options** * **Option A (1000 mL/min):** This is a common distractor for students who incorrectly assume a standard RBF without calculating based on the provided Hct. * **Option C (1200 mL/min):** This value is often cited as the "average" RBF in a 70kg male, but it does not fit the specific parameters given in this mathematical problem. * **Option D (1250 mL/min):** This would be the result if the Hct were 52% or if the student confused the calculation with GFR/Filtration Fraction constants. **3. Clinical Pearls & High-Yield Facts for NEET-PG** * **Normal RBF:** Approximately 1100–1200 mL/min (roughly 20-25% of Cardiac Output). * **Normal RPF:** Approximately 600–650 mL/min. * **Filtration Fraction (FF):** $\text{GFR} / \text{RPF}$ (Normal $\approx 0.20$ or 20%). * **Gold Standard for RPF:** Para-aminohippuric acid (PAH) clearance, as it is both filtered and secreted. * **Autoregulation:** RBF remains constant between a Mean Arterial Pressure (MAP) of **80–180 mmHg** via myogenic and tubuloglomerular feedback mechanisms.

Q: Autosomal variant of nephrogenic diabetes insipidus is due to defect in which of the following?

Aquaporin 2. **Explanation:** **Nephrogenic Diabetes Insipidus (NDI)** is characterized by the kidney's inability to concentrate urine despite adequate levels of Antidiuretic Hormone (ADH/Vasopressin). * **Why Aquaporin 2 is correct:** ADH normally binds to V2 receptors on the basolateral membrane of the collecting duct, triggering a cAMP pathway that inserts **Aquaporin-2 (AQP2)** channels into the apical membrane to facilitate water reabsorption. * The most common form of hereditary NDI is **X-linked recessive** (90%), caused by a mutation in the **V2 receptor**. * The **Autosomal (recessive or dominant) variant** of NDI is caused by mutations in the **Aquaporin-2 gene**, leading to defective water channels. **Analysis of Incorrect Options:** * **Options B & C (Angiotensin I & II receptors):** These are involved in blood pressure regulation and aldosterone secretion via the Renin-Angiotensin-Aldosterone System (RAAS). They do not directly mediate the water-permeability effects of ADH in the collecting duct. * **Option D (VIP receptors):** Vasoactive Intestinal Peptide (VIP) is involved in smooth muscle relaxation and intestinal secretion, but it plays no role in the renal concentrating mechanism associated with Diabetes Insipidus. **High-Yield Clinical Pearls for NEET-PG:** * **Lithium:** The most common cause of *acquired* nephrogenic DI (it inhibits cAMP formation). * **V1 Receptors:** Located on vascular smooth muscle (cause vasoconstriction). * **V2 Receptors:** Located in the principal cells of the collecting duct (mediate water reabsorption). * **Diagnosis:** NDI is confirmed when there is no increase in urine osmolality following the administration of exogenous ADH (Desmopressin) during a water deprivation test.

Q: Ion ligand receptors are:

Glycine receptor. **Explanation:** The question asks to identify an **Ionotropic receptor** (Ion-ligand gated channel). These are membrane proteins that act as both a receptor and an ion channel, allowing rapid flux of ions across the cell membrane upon ligand binding. **1. Why Glycine receptor is correct:** The **Glycine receptor** is a classic example of an ionotropic receptor. It is a ligand-gated **chloride (Cl⁻) channel**. When glycine binds, the channel opens, leading to Cl⁻ influx, which causes hyperpolarization of the postsynaptic membrane, resulting in fast inhibitory neurotransmission (primarily in the spinal cord and brainstem). Other examples include Nicotinic ACh, GABA-A, and NMDA receptors. **2. Why other options are incorrect:** * **Beta-adrenergic receptors:** These belong to the **G-Protein Coupled Receptor (GPCR)** family (specifically Gs). They work via the adenylyl cyclase-cAMP second messenger system, not by direct ion gating. * **V1 receptor:** These are Vasopressin receptors (V1a and V1b) that are **GPCRs** coupled to the Gq pathway, activating Phospholipase C and increasing intracellular calcium. * **Insulin receptor:** This is an **Enzyme-linked receptor** (specifically a Receptor Tyrosine Kinase). Binding triggers autophosphorylation of tyrosine residues, initiating a phosphorylation cascade. **High-Yield Clinical Pearls for NEET-PG:** * **Strychnine:** A potent convulsant that acts as a competitive antagonist at Glycine receptors, leading to unchecked muscular contractions. * **Fastest Receptors:** Ionotropic receptors (milliseconds) > GPCRs (seconds) > Enzyme-linked (minutes/hours) > Nuclear receptors (hours/days). * **V2 Receptors:** Unlike V1, V2 receptors (found in renal collecting ducts) are GPCRs coupled to **Gs**, increasing cAMP to insert Aquaporin-2 channels.

Question 1

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

Accepted Answer

Aldosterone

Answer

Cortisol

Answer

Thyroxine

Answer

ACTH

Question 2

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 3

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 4

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 5

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

Question 6

Which of the following conditions results in increased secretion of Renin?

Accepted Answer

Decreased amount of Na+ in the proximal convoluted tubule (PCT)

Answer

Renal ischemia

Answer

Decreased amount of Na+ in the distal convoluted tubule (DCT)

Answer

Narrowing of afferent arterioles

Question 7

What is the minimum urine osmolality that the human kidney can achieve?

Accepted Answer

50 mOsm/L

Answer

100 mOsm/L

Answer

80 mOsm/L

Answer

20 mOsm/L

Question 8

If the renal plasma flow (RPF) is 600 mL/min and the hematocrit (hct) is 45%, what is the renal blood flow?

Accepted Answer

1090 mL/min

Answer

1000 mL/min

Answer

1200 mL/min

Answer

1250 mL/min

Question 9

Autosomal variant of nephrogenic diabetes insipidus is due to defect in which of the following?

Accepted Answer

Aquaporin 2

Answer

Angiotensin I receptor

Answer

Angiotensin II receptor

Answer

VIP receptors

Question 10

Ion ligand receptors are:

Accepted Answer

Glycine receptor

Answer

beta adrenergic receptors

Answer

V1 receptor

Answer

Insulin receptor

Renal Physiology — MCQs

Renal Physiology — MCQs

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