Renal Physiology Practice Questions

Q: What percentage of total nephrons are juxtamedullary nephrons?

15%. **Explanation:** In the human kidney, nephrons are classified into two distinct types based on their location and structural characteristics: **Cortical nephrons** and **Juxtamedullary nephrons**. 1. **Why 15% is correct:** Approximately **15%** (range 12–15%) of all nephrons are juxtamedullary nephrons. Their glomeruli are located in the inner third of the renal cortex, near the medulla. They possess long Loops of Henle that descend deep into the renal medulla, often reaching the tips of the renal papillae. Their primary physiological role is the **concentration of urine** via the countercurrent multiplier system. 2. **Why other options are incorrect:** * **85% (Inverse of Option A):** This represents the majority of nephrons, which are **Cortical nephrons**. These have short loops and are primarily responsible for waste excretion and nutrient reabsorption. * **50%, 70%, and 90%:** These values do not correspond to any standard anatomical distribution of nephron types in a healthy human kidney. **High-Yield Facts for NEET-PG:** * **Vasa Recta:** Juxtamedullary nephrons are uniquely associated with the *vasa recta* (specialized peritubular capillaries), which are essential for maintaining the medullary osmotic gradient. * **Concentrating Capacity:** Species living in arid environments (like the kangaroo rat) have a much higher percentage of juxtamedullary nephrons to conserve water. * **Renin Content:** Juxtamedullary nephrons generally contain higher amounts of renin compared to cortical nephrons. * **Blood Flow:** Although juxtamedullary nephrons are vital for concentration, the majority of renal blood flow (approx. 90%) is directed to the renal cortex.

Q: Which of the following is not a correct association regarding the renin-angiotensin-aldosterone system?

Renin - liver. ### Explanation The **Renin-Angiotensin-Aldosterone System (RAAS)** is a critical hormonal cascade for blood pressure regulation and fluid balance. **Why Option A is the correct answer:** **Renin** is an enzyme synthesized, stored, and secreted by the **Juxtaglomerular (JG) cells** of the afferent arterioles in the **kidney**, not the liver. Its primary role is to cleave Angiotensinogen into Angiotensin I. Therefore, the association of Renin with the liver is incorrect. **Analysis of other options:** * **B. Renin - kidney:** This is a correct association. JG cells (modified smooth muscle cells) in the kidney release renin in response to low perfusion pressure, sympathetic stimulation, or decreased sodium delivery to the macula densa. * **C. Renin substrate - liver:** This is a correct association. **Angiotensinogen** (the substrate for renin) is a plasma protein synthesized and continuously released into the circulation by the **liver**. * **D. ACE - lung endothelium:** This is a correct association. **Angiotensin-Converting Enzyme (ACE)** is primarily located on the luminal surface of vascular endothelial cells, with the highest concentration found in the **pulmonary capillaries**. **High-Yield NEET-PG Pearls:** * **Rate-limiting step:** The release of **Renin** is the rate-limiting step of the RAAS pathway. * **Stimuli for Renin release:** 1. Decreased renal perfusion (Baroreceptor mechanism), 2. Decreased NaCl at Macula Densa, 3. Increased Sympathetic activity ($\beta_1$ receptors). * **ACE Inhibitors:** Common side effect is a dry cough due to the accumulation of **Bradykinin** in the lungs, as ACE is also responsible for bradykinin degradation. * **Angiotensin II:** A potent vasoconstrictor that also stimulates the **Zona Glomerulosa** of the adrenal cortex to secrete **Aldosterone**.

Q: Maximum absorption of NaCl in the proximal convoluted tubule occurs due to the effect of:

Angiotensin II. **Explanation:** The **Proximal Convoluted Tubule (PCT)** is the primary site for the reabsorption of water and solutes (approximately 65-70% of the filtered load). **Angiotensin II** is the most potent stimulator of NaCl and water reabsorption in the PCT. **Why Angiotensin II is correct:** Angiotensin II acts on the **NHE3 (Sodium-Hydrogen Exchanger)** on the apical membrane and the **Na+/K+ ATPase** on the basolateral membrane of the PCT cells. By stimulating these transporters, it directly increases sodium reabsorption. Additionally, by constricting the efferent arteriole, it increases the filtration fraction, leading to increased peritubular capillary oncotic pressure, which further facilitates fluid reabsorption from the PCT. **Why other options are incorrect:** * **ADH (Vasopressin):** Primarily acts on the **Collecting Ducts** (V2 receptors) to increase water permeability via Aquaporin-2 channels. It has minimal effect on NaCl reabsorption in the PCT. * **Aldosterone:** Acts on the **Principal cells of the Late Distal Tubule and Collecting Duct**. It promotes Na+ reabsorption and K+ secretion by upregulating ENaC channels and Na+/K+ ATPase. * **Atrial Natriuretic Peptide (ANP):** This is a "natriuretic" hormone; it **inhibits** Na+ reabsorption in the medullary collecting duct and inhibits the secretion of Renin and Aldosterone to decrease blood pressure. **High-Yield Clinical Pearls for NEET-PG:** * **PCT** is the site for 100% reabsorption of Glucose and Amino acids. * **Carbonic Anhydrase inhibitors (Acetazolamide)** act specifically on the PCT. * **Angiotensin II** is unique because it maintains GFR (via efferent constriction) while simultaneously increasing Na+ reabsorption to expand ECF volume.

Q: Osmoreceptors are located in which of the following areas?

Supraoptic nuclei. **Explanation:** The regulation of water balance is primarily governed by **osmoreceptors**, which are specialized neurons that detect changes in plasma osmolarity. **1. Why Supraoptic Nuclei (SON) is correct:** The osmoreceptors are primarily located in the **anterior hypothalamus**, specifically within the **Supraoptic Nuclei (SON)** and the **Organum Vasculosum of the Lamina Terminalis (OVLT)**. When plasma osmolarity increases (e.g., dehydration), these receptors shrink, triggering an action potential. This stimulates the synthesis and release of **Antidiuretic Hormone (ADH/Vasopressin)** from the SON, which then travels via the hypothalamo-hypophyseal tract to the posterior pituitary for secretion into the blood. **2. Why other options are incorrect:** * **Paraventricular nuclei (PVN):** While the PVN also produces ADH, its primary function is the synthesis of **Oxytocin**. It is less involved in osmoreception compared to the SON. * **Anterior hypothalamus:** While the SON is *located* in the anterior hypothalamus, the question asks for the specific site. In NEET-PG, the most specific anatomical structure (SON) is preferred over the general region. * **Lateral hypothalamus:** This area is known as the **"Feeding Center."** Stimulation leads to hunger, while lesions lead to aphagia and weight loss. **High-Yield Clinical Pearls for NEET-PG:** * **Primary Stimulus for ADH:** A mere 1% change in osmolarity triggers ADH release. * **Thirst Center:** Located in the lateral preoptic area. * **Circumventricular Organs:** The OVLT and SFO (Subfornical Organ) lack a blood-brain barrier, allowing them to sense systemic osmolarity directly. * **Diabetes Insipidus:** Damage to the SON or the tract leads to Central DI, characterized by polyuria and low urine osmolarity.

Q: Glucose is reabsorbed in the proximal tubule via symport with which ion?

Na+. **Explanation:** Glucose reabsorption in the proximal convoluted tubule (PCT) occurs via **Secondary Active Transport**. This process is mediated by **Sodium-Glucose Co-transporters (SGLT)**, specifically SGLT2 (early PCT) and SGLT1 (late PCT). **Why Na+ is correct:** The process is driven by the electrochemical gradient created by the **Na+-K+ ATPase pump** on the basolateral membrane, which keeps intracellular sodium levels low. This gradient allows sodium to move down its concentration gradient from the tubular lumen into the cell. Glucose "hitchhikes" with sodium against its own concentration gradient via a **symport** mechanism. Once inside the cell, glucose exits the basolateral membrane into the blood via facilitated diffusion through **GLUT2** (or GLUT1). **Why other options are incorrect:** * **K+ (Potassium):** Potassium is primarily secreted or reabsorbed through specific channels and exchangers (like the Na-K-2Cl symporter in the Loop of Henle), but it does not drive glucose transport. * **Ca++ (Calcium):** Calcium reabsorption in the PCT is largely passive (paracellular) and follows water and sodium; it is not coupled with glucose. * **Cl- (Chloride):** Chloride is reabsorbed primarily via paracellular pathways or in exchange for other anions in the later segments of the PCT. **High-Yield Clinical Pearls for NEET-PG:** * **SGLT2 Inhibitors (e.g., Dapagliflozin):** A class of drugs used in Diabetes Mellitus that block glucose reabsorption in the PCT, leading to glucosuria. * **Renal Threshold for Glucose:** Approximately **180 mg/dL**. When blood glucose exceeds this, SGLT transporters become saturated ($T_mG$), and glucose appears in the urine. * **Fanconi Syndrome:** A generalized dysfunction of the PCT resulting in the loss of glucose, amino acids, and phosphates in the urine.

Q: What will be the plasma clearance value of glucose in a patient with diabetes mellitus?

Greater than zero. **Explanation:** The plasma clearance of a substance is the volume of plasma from which that substance is completely removed by the kidneys per unit time. **1. Why the Correct Answer is Right:** In a healthy individual, the plasma clearance of glucose is **zero** because all filtered glucose is reabsorbed in the proximal convoluted tubule (PCT) via SGLT-2 transporters. However, in **Diabetes Mellitus**, the filtered load of glucose often exceeds the **Renal Threshold** (approx. 180 mg/dL) and the **Tubular Transport Maximum ($T_mG$)** (approx. 375 mg/min in men). Once the transporters are saturated, the excess glucose cannot be reabsorbed and is excreted in the urine (glycosuria). Since glucose is now being cleared from the plasma into the urine, the clearance value becomes **greater than zero**. **2. Why the Incorrect Options are Wrong:** * **Option A (Zero):** This is true for healthy individuals, but not for diabetics with hyperglycemia exceeding the renal threshold. * **Option B (Equal to Inulin):** Inulin clearance represents the GFR because it is filtered but neither reabsorbed nor secreted. For glucose clearance to equal inulin, zero reabsorption would have to occur, which is not the case even in diabetes. * **Option C (Greater than PAH):** PAH clearance represents Renal Plasma Flow (RPF) because it is filtered and maximally secreted. No substance can have a clearance higher than the RPF. **3. Clinical Pearls for NEET-PG:** * **Renal Threshold for Glucose:** ~180 mg/dL (venous blood). * **Splay:** The curve representing the difference between the theoretical and actual renal threshold due to the heterogeneity of nephrons and low affinity of transporters. * **SGLT-2 Inhibitors (e.g., Dapagliflozin):** These drugs intentionally lower the renal threshold to induce glycosuria, thereby increasing glucose clearance to treat Type 2 Diabetes.

Question 1

What percentage of total nephrons are juxtamedullary nephrons?

Accepted Answer

15%

Answer

50%

Answer

70%

Answer

90%

Question 2

Which of the following is not a correct association regarding the renin-angiotensin-aldosterone system?

Accepted Answer

Renin - liver

Answer

Renin - kidney

Answer

Renin substrate - liver

Answer

ACE - lung endothelium

Question 3

Maximum absorption of NaCl in the proximal convoluted tubule occurs due to the effect of:

Accepted Answer

Angiotensin II

Answer

ADH

Answer

Aldosterone

Answer

Atrial natriuretic peptide

Question 4

Osmoreceptors are located in which of the following areas?

Accepted Answer

Supraoptic nuclei

Answer

Paraventricular nuclei

Answer

Anterior hypothalamus

Answer

Lateral hypothalamus

Question 5

Which of the following renal alterations would most likely preserve the Glomerular Filtration Rate (GFR)?

Accepted Answer

Decreased intrarenal nitric oxide

Answer

Defect in the elimination of hydrogen ions in the distal tubule

Answer

Luminal obstruction by renal tubular casts

Answer

Increased interstitial pressure

Question 6

A substance is present in a concentration of 2 mg% in the afferent arteriole and zero mg% in the efferent arteriole. What is true about this substance?

Accepted Answer

It is freely filtered at the glomerulus.

Answer

It is secreted in the cortical nephron.

Answer

It is absorbed in the proximal convoluted tubule.

Answer

It is impermeable in the loop of Henle.

Question 7

Net filtration pressure of the glomerulus increases when which of the following occurs?

Accepted Answer

Increase in hydrostatic pressure of the glomerular capillary

Answer

Increase in oncotic pressure of the glomerular capillary

Answer

Increase in hydrostatic pressure of Bowman's space

Answer

All of the above

Question 8

Glucose is reabsorbed in the proximal tubule via symport with which ion?

Accepted Answer

Na+

Answer

K+

Answer

Ca++

Answer

Cl-

Question 9

Glucosuria occurs when the venous blood glucose concentration exceeds which of the following values?

Accepted Answer

10 mg/dL

Answer

100 mg/dL

Answer

180 mg/dL

Answer

18 mg/dL

Question 10

What will be the plasma clearance value of glucose in a patient with diabetes mellitus?

Accepted Answer

Greater than zero

Answer

Zero

Answer

Equal to that of inulin clearance

Answer

Greater than that of PAH clearance

Renal Physiology — MCQs

Renal Physiology — MCQs

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