Renal Physiology Practice Questions

Q: Which of the following statements about aquaporins is false?

Aquaporin-2 in loop of Henle. ***Aquaporin-2 in loop of Henle (FALSE - Correct Answer)*** - **Aquaporin-2 (AQP2)** is primarily found in the apical membrane of the **collecting duct (CD)**, NOT in the loop of Henle. - Its presence and function in the CD are regulated by **vasopressin (ADH)**, which promotes water reabsorption. - This statement is **false** and is therefore the correct answer to this question. *Aquaporins are proteins (TRUE)* - Aquaporins are indeed a **family of integral membrane proteins** that function as water channels. - They facilitate the rapid movement of water across cell membranes, playing a crucial role in water balance. - This statement is **true**. *Aquaporin-1 in PCT (TRUE)* - **Aquaporin-1 (AQP1)** is abundantly expressed in the **proximal convoluted tubule (PCT)** and the descending limb of the loop of Henle. - It allows for constitutive, unregulated water reabsorption driven by osmotic gradients. - This statement is **true**. *Aquaporin-2 in CD (TRUE)* - **Aquaporin-2 (AQP2)** is correctly located in the apical membrane of the principal cells of the **collecting duct (CD)**. - Its insertion into the membrane and water permeability are regulated by **antidiuretic hormone (ADH)**, making it vital for facultative water reabsorption. - This statement is **true**.

Q: Plasma inulin of a person is 4 mg/ml and urine flow rate is 20 ml/min. What will be GFR if urine inulin is 50 mg/ml?

250 ml/min. ***250 ml/min*** - Glomerular Filtration Rate (GFR) can be calculated using the **clearance formula**: GFR = (Urine Inulin Concentration × Urine Flow Rate) / Plasma Inulin Concentration. - Plugging in the values: (50 mg/ml × 20 ml/min) / 4 mg/ml = 1000 / 4 = **250 ml/min**. *125 ml/min* - This value would be obtained if the urine inulin concentration was lower or if the plasma inulin concentration was higher, resulting in a lower GFR. - For example, if plasma inulin were 8 mg/ml with the other values unchanged, the GFR would be 125 ml/min. *500 ml/min* - This result would be reached if the urine inulin concentration was significantly higher or if the plasma inulin concentration was lower than given. - For instance, if the urine flow rate were 40 ml/min instead of 20 ml/min, GFR would be 500 ml/min. *1000 ml/min* - This GFR is a significantly higher value than typically observed and would require a much larger urine inulin concentration or urine flow rate, or a much lower plasma inulin concentration. - This value would be obtained if the plasma inulin concentration was 1 mg/ml with the given urine inulin and flow rate.

Q: What decreases renin secretion?

High NaCl concentration in distal tubules. ***High NaCl concentration in distal tubules*** - Increased **NaCl concentration** in the **distal tubules** is sensed by the **macula densa** cells, which then **actively inhibit renin release** from the juxtaglomerular cells through adenosine and ATP signaling. - This is part of the **tubuloglomerular feedback mechanism**, a direct negative feedback that reduces glomerular filtration rate and maintains electrolyte balance. - This represents **active suppression** of renin secretion. *Increased sympathetic stimulation* - **Increased sympathetic output** to the kidney, primarily via **beta-1 adrenergic receptors**, directly **stimulates renin secretion**. - This response is part of the body's reaction to stress or hypovolemia to raise blood pressure. *Decreased prostacycline [PGI2]* - **Prostacyclin (PGI2)** is a **vasodilator** that acts locally to **stimulate renin release**. - A **decrease in PGI2** represents **loss of a stimulatory signal** rather than active inhibition of renin. - This is a **permissive factor** - its absence doesn't actively decrease renin, it simply removes one of several stimulatory influences. - The question asks what *decreases* renin, implying active suppression rather than mere absence of stimulation. *Severe hypotension* - **Severe hypotension** leads to a **decrease in renal perfusion pressure**, which is detected by **baroreceptors** in the juxtaglomerular apparatus. - This is a powerful stimulus for **increased renin secretion** via the intrarenal baroreceptor mechanism. - This response is crucial for activating the **renin-angiotensin-aldosterone system (RAAS)** to restore blood pressure.

Q: What is the primary function of Lacis cells in the nephron?

Regulation of glomerular filtration rate. ***Regulation of glomerular filtration rate*** - Lacis cells, also known as extraglomerular mesangial cells, are part of the **juxtaglomerular apparatus** (JGA). - They play a crucial role in the **autoregulation** of the **glomerular filtration rate (GFR)** by transmitting signals between the macula densa and the afferent arteriole. *Secretion of renin to regulate blood pressure* - The primary cells responsible for **renin secretion** are the **juxtaglomerular cells** (granular cells) located in the walls of the afferent arteriole. - While Lacis cells are part of the JGA, their direct role in renin secretion is minimal compared to juxtaglomerular cells. *Reabsorption of sodium ions* - **Sodium reabsorption** primarily occurs in the **renal tubules**, particularly the **proximal tubule** and the **Loop of Henle**. - Lacis cells are not directly involved in the tubular reabsorption of electrolytes. *Regulation of blood flow in arterioles* - While Lacis cells communicate with the afferent and efferent arterioles, their main function is not to directly regulate blood flow but rather to mediate the **tubuloglomerular feedback** mechanism to control GFR. - The **smooth muscle cells** within the arteriolar walls are primarily responsible for regulating blood flow.

Q: Impaired function of Aquaporin results in

Nephrogenic DI. ***Nephrogenic DI*** - **Nephrogenic Diabetes Insipidus (DI)** results from the kidneys' inability to respond to **vasopressin (ADH)** due to defects in **V2 receptors** or, more commonly, mutations in **Aquaporin-2** (AQP2) water channels. - This leads to the excretion of large volumes of dilute urine, as water cannot be reabsorbed by the collecting ducts even when ADH levels are adequate. *Liddle syndrome* - This is an **autosomal dominant** disorder characterized by unregulated activation of the **epithelial sodium channel (ENaC)** in the collecting tubules. - It leads to increased sodium reabsorption, hypertension, hypokalemia, and metabolic alkalosis, not directly related to aquaporin function. *Cystic fibrosis* - This is an **autosomal recessive** genetic disorder that affects cells that produce mucus, sweat, and digestive juices, primarily due to mutations in the **CFTR (cystic fibrosis transmembrane conductance regulator) gene**. - Impaired CFTR protein function leads to thick, sticky secretions that can block ducts and passages, primarily in the lungs and pancreas, and is unrelated to aquaporin function. *Bartter syndrome* - This is a group of **autosomal recessive** disorders characterized by impaired reabsorption of sodium and chloride in the **thick ascending limb of the loop of Henle**. - It leads to significant urine loss of sodium, potassium, and chloride, resulting in hypokalemia, metabolic alkalosis, hypercalciuria, and often normal to low blood pressure, not directly related to aquaporin.

Q: Which of the following is NOT a component responsible for the counter current mechanism in the kidney?

Flow of tubular fluid from PCT to DCT. ***Flow of tubular fluid from PCT to DCT*** - While tubular fluid flow through the nephron is necessary for overall kidney function, it is **NOT a specific component of the countercurrent mechanism** itself. - The countercurrent mechanism specifically refers to the **countercurrent multiplier system** in the **Loop of Henle**, which creates and maintains the medullary osmotic gradient. - The flow from PCT to DCT is simply the sequential passage of fluid through nephron segments, not a specific mechanism for creating the hypertonic medullary interstitium. *Sodium outflow in thick ascending limb* - The **thick ascending limb** actively transports **Na+, K+, and Cl- ions** (via Na-K-2Cl cotransporter) out of the tubule into the medullary interstitium. - This segment is **impermeable to water**, allowing solute removal without water, creating a **dilute tubular fluid** and **hypertonic interstitium**. - This is the **primary active component** of the countercurrent multiplier mechanism. *Water outflow in thin descending limb* - The **thin descending limb** is highly permeable to **water** but relatively impermeable to solutes. - As tubular fluid descends into the hypertonic medulla, water passively moves out, **concentrating the tubular fluid**. - This passive water reabsorption is essential for the countercurrent mechanism. *Sodium outflow in thin ascending limb* - The **thin ascending limb** is permeable to Na+ and Cl-, allowing **passive diffusion** of these ions into the medullary interstitium. - Though less significant than the active transport in the thick ascending limb, this passive sodium outflow **contributes to the osmotic gradient** in the medulla. - This segment is also **impermeable to water**, preventing water reabsorption while allowing solute loss.

Q: Vasopressin acts through which aquaporin channels in the collecting duct?

Aquaporin 2. ***Aquaporin 2*** - Vasopressin (ADH) stimulates the insertion of **Aquaporin 2 (AQP2)** channels into the apical membrane of collecting duct cells, increasing water reabsorption. - This process is crucial for the kidney's ability to concentrate urine and maintain **water balance**. *Aquaporin 1* - **Aquaporin 1 (AQP1)** is predominantly found in the proximal tubules and descending limb of the loop of Henle, where **constitutive water reabsorption** occurs, independent of vasopressin. - It plays a role in bulk water reabsorption rather than regulated fine-tuning. *Aquaporin 3* - **Aquaporin 3 (AQP3)** is located on the **basolateral membrane** of collecting duct cells, facilitating the exit of water from the cell into the interstitial fluid. - While essential for water movement, its insertion into the membrane is **not directly regulated by vasopressin** in the same way as AQP2. *Aquaporin 4* - **Aquaporin 4 (AQP4)** is also found on the **basolateral membrane** of collecting duct cells and in other tissues like the brain. - Similar to AQP3, it allows water to leave the cell but is not the primary target for vasopressin-mediated regulation of water permeability.

Q: What is the physiological response of the kidney during shock?

Renal blood flow decreases. ***Renal blood flow decreases*** - During shock, the **primary and most fundamental** physiological change affecting the kidney is a marked **reduction in renal blood flow (RBF)**. - Shock triggers intense **sympathetic activation** and **renin-angiotensin system (RAS) activation**, causing preferential **vasoconstriction** of renal vessels to redirect blood to vital organs (brain, heart). - RBF can drop to as low as **20-30% of normal** in severe shock, making this the hallmark renal response. - This reduction in RBF is the **upstream event** that triggers all other renal changes during shock. *Perfusion of kidney decreases* - While technically correct, "decreased perfusion" is **essentially synonymous** with decreased blood flow in this context. - The term "renal blood flow" is the **standard physiological terminology** used in medical literature to describe this phenomenon, making it the more precise answer. *Afferent arteriole resistance increases* - This is a **mechanism** by which RBF decreases, not the overall response itself. - Increased afferent arteriolar resistance is **secondary** to sympathetic activation and angiotensin II effects during shock. - It describes the "how" rather than the "what" of the kidney's response. *GFR decreases* - GFR reduction is a **consequence** of decreased RBF and increased afferent arteriolar resistance. - While clinically important (oliguria/acute kidney injury), it's a **downstream effect** rather than the primary physiological response. - The relationship: ↓RBF → ↓Glomerular hydrostatic pressure → ↓GFR

Question 1

Which of the following statements is true regarding the function of the distal convoluted tubule?

Accepted Answer

Reabsorbs sodium primarily via sodium-chloride symporters.

Answer

Reabsorbs chloride ions via sodium-chloride symporters.

Answer

Reabsorbs water in response to ADH.

Answer

All of the options.

Question 2

Which of the following statements about aquaporins is false?

Accepted Answer

Aquaporin-2 in loop of Henle

Answer

Aquaporins are proteins

Answer

Aquaporin-1 in PCT

Answer

Aquaporin-2 in CD

Question 3

Plasma inulin of a person is 4 mg/ml and urine flow rate is 20 ml/min. What will be GFR if urine inulin is 50 mg/ml?

Accepted Answer

250 ml/min

Answer

125 ml/min

Answer

500 ml/min

Answer

1000 ml/min

Question 4

What decreases renin secretion?

Accepted Answer

High NaCl concentration in distal tubules

Answer

Increased sympathetic stimulation

Answer

Decreased prostacycline [PGI2]

Answer

Severe hypotension

Question 5

What is the primary function of Lacis cells in the nephron?

Accepted Answer

Regulation of glomerular filtration rate

Answer

Secretion of renin to regulate blood pressure

Answer

Reabsorption of sodium ions

Answer

Regulation of blood flow in arterioles

Question 6

Which of the following statements is true regarding the given cystometrogram?

Accepted Answer

Segment Ib reflects the bladder's ability to accommodate increasing volume without a significant rise in pressure.

Answer

Segment II represents the initial filling phase, during which intravesical pressure remains low and stable.

Answer

Segment Ia represents residual urine, not the initial phase of bladder filling.

Answer

Micturition occurs in segment Ib; failure to micturate is characteristic of this segment.

Question 7

Impaired function of Aquaporin results in

Accepted Answer

Nephrogenic DI

Answer

Liddle syndrome

Answer

Cystic fibrosis

Answer

Bartter syndrome

Question 8

Which of the following is NOT a component responsible for the counter current mechanism in the kidney?

Accepted Answer

Flow of tubular fluid from PCT to DCT

Answer

Sodium outflow in thick ascending limb

Answer

Sodium outflow in thin ascending limb

Answer

Water outflow in thin descending limb

Question 9

Vasopressin acts through which aquaporin channels in the collecting duct?

Accepted Answer

Aquaporin 2

Answer

Aquaporin 1

Answer

Aquaporin 4

Answer

Aquaporin 3

Question 10

What is the physiological response of the kidney during shock?

Accepted Answer

Renal blood flow decreases

Answer

GFR decreases

Answer

Perfusion of kidney decreases

Answer

Afferent arteriole resistance increases

Renal Physiology — MCQs

Renal Physiology — MCQs

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