Renal Physiology

Renal Physiology Indian Medical PG Question 1: Which carrier pump is responsible for transporting solutes in the thick ascending limb of the loop of Henle?

• A. NaCl cotransporter
• B. Na+-H+ exchanger
• C. Na+-K+ exchanger
• D. Sodium-potassium-chloride cotransporter (Correct Answer)

Renal Physiology Explanation: * **Sodium-potassium-chloride cotransporter.** * This transporter, specifically the **Na+-K+-2Cl- cotransporter (NKCC2)**, is highly expressed in the apical membrane of the thick ascending limb. * It actively reabsorbs **sodium, potassium, and chloride ions** from the filtrate, contributing significantly to the medullary interstitial osmotic gradient. * *NaCl- cotransporter* * The **NaCl cotransporter (NCC)** is primarily found in the **distal convoluted tubule**, not the thick ascending limb. * It reabsorbs sodium and chloride in a 1:1 ratio and is the target of thiazide diuretics. * *Na+-H+ exchanger* * The **Na+-H+ exchanger (NHE3)** is predominantly located in the **proximal tubule** where it plays a crucial role in bicarbonate reabsorption and acid-base balance. * While some NHE activity exists in other nephron segments, it is not the primary carrier in the thick ascending limb. * *Na+-K+ exchanger* * The **Na+-K+ exchanger** or **Na+/K+-ATPase pump** is located on the basolateral membrane of most renal tubular cells, including the thick ascending limb. * Its main function is to maintain the electrochemical gradient by pumping **sodium out of the cell** and potassium into the cell, which indirectly drives other transporters but is not the apical cotransporter responsible for initial solute reabsorption in the thick ascending limb.

Renal Physiology Indian Medical PG Question 2: A healthy 22-year-old female medical student with normal kidneys decreases her sodium intake by 50% for a period of 2 months. Which of the following parameters is expected to increase in response to the reduction in sodium intake?

• A. Atrial natriuretic peptide release
• B. Extracellular fluid volume
• C. Arterial pressure
• D. Renin release (Correct Answer)

Renal Physiology Explanation: ***Renin release*** - A reduction in **sodium intake** leads to decreased extracellular fluid volume and **reduced renal perfusion pressure**, which stimulates **renin release** from the juxtaglomerular cells. - Renin initiates the **renin-angiotensin-aldosterone system (RAAS)**, leading to **angiotensin II** formation and increased **aldosterone** secretion, aimed at sodium and water retention. *Atrial natriuretic peptide release* - **Atrial natriuretic peptide (ANP)** release is stimulated by **atrial stretch** due to increased blood volume and pressure, which would decrease with reduced sodium intake. - Therefore, ANP release would likely **decrease** or remain unchanged, not increase, in response to chronic sodium restriction. *Extracellular fluid volume* - A decrease in sodium intake directly leads to a **reduction in total body sodium**, which is the primary determinant of **extracellular fluid volume**. - The body attempts to maintain fluid balance, but chronic sodium restriction will ultimately lead to a **decrease** in extracellular fluid volume as the kidneys excrete less water to match the lower sodium intake. *Arterial pressure* - Reduced sodium intake typically leads to a **decrease in extracellular fluid volume** and **cardiac output**, which in turn causes a **reduction in arterial blood pressure**. - The activation of the RAAS aims to mitigate this drop but usually does not fully compensate to increase pressure above baseline in this scenario.

Renal Physiology Indian Medical PG Question 3: Which of the following statements are correct regarding renal cell carcinoma? 1. It arises from the epithelium of the proximal convoluted tubule. 2. It has a female preponderance. 3. Major subtypes are clear cell, papillary and chromophobe. 4. Surgery is the mainstay of treatment for organ-confined disease. Select the answer using the code given below.

• A. 1, 2 and 3
• B. 1, 3 and 4 (Correct Answer)
• C. 1, 2 and 4
• D. 2, 3 and 4

Renal Physiology Explanation: ***1, 3 and 4*** - **Renal cell carcinoma (RCC)** most commonly arises from the **epithelium of the proximal convoluted tubule**, particularly the clear cell subtype [1]. This makes statement 1 correct. - The major subtypes of RCC are indeed **clear cell, papillary, and chromophobe carcinomas**, accounting for the vast majority of cases [1]. This validates statement 3. - For **organ-confined renal cell carcinoma**, **surgical resection (nephrectomy)** remains the primary and most effective treatment modality, making statement 4 correct. [1] *1, 2 and 3* - This option incorrectly includes statement 2, which claims a female preponderance for RCC. **Renal cell carcinoma is more common in males** than females, not the reverse [1]. - While statements 1 and 3 are correct regarding the origin and major subtypes of RCC, the inclusion of an incorrect epidemiological fact makes this option wrong. *1, 2 and 4* - This option falls short by incorrectly including statement 2, which asserts a female predominance for RCC. **RCC has a male predominance**, with a male-to-female ratio of about 2:1 [1]. - This option also omits statement 3, which correctly identifies the major subtypes (clear cell, papillary, and chromophobe), even though statements 1 and 4 are correct. *2, 3 and 4* - This option incorrectly includes statement 2, which states a female preponderance for RCC; **renal cell carcinoma is actually more prevalent in males** [1]. - While statements 3 and 4 are correct regarding the major subtypes and the role of surgery in organ-confined disease, the factual error in statement 2 invalidates this option.

Renal Physiology Indian Medical PG Question 4: GFR is increased by all except?

• A. Renal stone in ureter (Correct Answer)
• B. Efferent arteriole constriction
• C. Increased renal blood flow
• D. Decreased oncotic pressure

Renal Physiology Explanation: ***Renal stone in ureter*** - A renal stone in the ureter causes **post-renal obstruction**, leading to a buildup of pressure in the Bowman's capsule, which in turn **reduces GFR**. - **Obstruction** impedes urine outflow, thereby increasing **hydrostatic pressure** in the tubular system and opposing filtration. *Efferent arteriole constriction* - **Constriction of the efferent arteriole** increases the **hydrostatic pressure** within the glomerulus, which promotes an increase in GFR. - This constriction retains blood in the glomerulus, thereby increasing the **filtration pressure**. *Increased renal blood flow* - An **increase in renal blood flow** elevates the **glomerular hydrostatic pressure** and increases the amount of plasma available for filtration, leading to an **increased GFR**. - A higher flow rate also helps to maintain a more constant **glomerular capillary oncotic pressure**, preventing early filtration equilibrium. *Decreased oncotic pressure* - **Decreased oncotic pressure** in the glomerular capillaries (e.g., due to hypoproteinemia) reduces the osmotic force opposing filtration. - This reduction in opposing force allows for a net increase in the **filtration pressure**, thereby **increasing GFR**.

Renal Physiology Indian Medical PG Question 5: Proteoglycan present in the glomerular basement membrane is?

• A. Keratan sulfate 1
• B. Keratan sulfate 2
• C. Heparan sulfate (Correct Answer)
• D. Chondroitin sulfate

Renal Physiology Explanation: ***Heparan sulphate*** - Heparan sulphate is a key component of the **glomerular basement membrane** (GBM), crucial for its **negative charge and filtration function** [1][2]. - It plays a significant role in **filtration barrier** properties and affects the permeability of the GBM to proteins [1]. *Keratan sulphate 1* - Predominantly found in **cartilage** and **corneal tissue**, not associated with the glomerular basement membrane. - It contributes to **mechanical support** but lacks the essential role in renal filtration. *Keratan sulphate 2* - Similar to Keratan sulphate 1, this variant is involved in **cartilage** but not in the structure of the glomerular basement membrane. - Has distinct functions related to **tissue hydration** rather than the filtration dynamics of the GBM. *Chondroitin sulphate* - Commonly located in **cartilage** and connective tissues, it does not play a significant role in the structure of the glomerular basement membrane. - While it assists in **cell signaling** and regeneration, it does not influence the GBM permeability like heparan sulphate. **References:** [1] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. The Kidney, pp. 905-907. [2] Kumar V, Abbas AK, et al.. Robbins and Cotran Pathologic Basis of Disease. 9th ed. With Illustrations By, pp. 34-35.

Renal Physiology Indian Medical PG Question 6: Match the following drugs in Column A with their contraindications in Column B. | Column A | Column B | | :-- | :-- | | 1. Morphine | 1. QT prolongation | | 2. Amiodarone | 2. Thromboembolism | | 3. Vigabatrin | 3. Pregnancy | | 4. Estrogen preparations | 4. Head injury |

• A. A-1, B-3, C-2, D-4
• B. A-4, B-1, C-3, D-2 (Correct Answer)
• C. A-3, B-2, C-4, D-1
• D. A-2, B-4, C-1, D-3

Renal Physiology Explanation: ***A-4, B-1, C-3, D-2*** - **Morphine** is contraindicated in **head injury** as it can increase intracranial pressure and mask neurological symptoms. - **Amiodarone** is contraindicated in patients with **QT prolongation** due to its risk of inducing more severe arrhythmias like Torsades de Pointes. - **Vigabatrin** is contraindicated during **pregnancy** due to its potential for teratogenicity and adverse effects on fetal development. - **Estrogen preparations** are contraindicated in patients with a history of **thromboembolism** due to their increased risk of blood clot formation. *A-1, B-3, C-2, D-4* - This option incorrectly matches **Morphine** with QT prolongation and **Estrogen preparations** with head injury, which are not their primary contraindications. - It also incorrectly links **Vigabatrin** with thromboembolism and **Amiodarone** with pregnancy. *A-3, B-2, C-4, D-1* - This choice incorrectly associates **Morphine** with pregnancy and **Vigabatrin** with head injury, which are not the most critical or direct contraindications. - It also misaligns **Amiodarone** with thromboembolism and **Estrogen preparations** with QT prolongation. *A-2, B-4, C-1, D-3* - This option incorrectly matches **Morphine** with thromboembolism and **Amiodarone** with head injury, which are not their most significant contraindications. - It also incorrectly links **Vigabatrin** with QT prolongation and **Estrogen preparations** with pregnancy.

Renal Physiology Indian Medical PG Question 7: Following surgery, a patient develops oliguria. You believe the patient is hypovolemic, but you seek corroborative data before increasing intravenous fluids. The best data is?

• A. Urine chloride of 15 meq/L
• B. Fractional excretion of sodium less than 1 (Correct Answer)
• C. Urine sodium of 28 meq/L
• D. Urine/Serum creatinine ratio of 20

Renal Physiology Explanation: ***Fractional excretion of sodium less than 1*** - A **fractional excretion of sodium (FENa) less than 1%** is a classic indicator of **prerenal azotemia** or hypovolemia, as the kidneys are avidly reabsorbing sodium and water to preserve circulating volume. - This indicates the kidneys are functioning appropriately in response to perceived hypoperfusion, attempting to conserve sodium and thus water. *Urine chloride of 15 meq/L* - While a **low urine chloride** can sometimes be seen in volume depletion, it is not as specific or reliable an indicator of hypovolemia as FENa. - Urine chloride is more helpful in differentiating causes of **metabolic alkalosis**, particularly saline-responsive versus saline-unresponsive. *Urine sodium of 28 meq/L* - A urine sodium concentration of **less than 20 mEq/L** is a more classic cutoff for prerenal azotemia/hypovolemia, indicating aggressive sodium reabsorption. - A value of 28 mEq/L, although relatively low, is less definitive than a low FENa in strongly supporting hypovolemia. *Urine/Serum creatinine ratio of 20* - A **urine/serum creatinine ratio greater than 20:1** is indicative of prerenal azotemia, suggesting the kidneys are concentrating urine in response to hypovolemia. - While supportive, FENa is often considered a more precise and widely accepted marker, especially in the absence of diuretic use or chronic kidney disease.

Renal Physiology Indian Medical PG Question 8: Which causes raised angiotensin in blood?

• A. Raised cardiac output
• B. Increased sympathetic tone
• C. Increased blood volume
• D. Decreased blood pressure (Correct Answer)

Renal Physiology Explanation: ***Decreased blood pressure*** - A decrease in blood pressure is the **primary physiological trigger** that signals the kidneys to release **renin**, initiating the **renin-angiotensin-aldosterone system (RAAS)**. - Renal baroreceptors in the juxtaglomerular apparatus sense decreased renal perfusion pressure and stimulate renin release. - Renin converts **angiotensinogen** to **angiotensin I**, which is then converted to **angiotensin II** (the active form) by **angiotensin-converting enzyme (ACE)**. - This represents the most direct and important mechanism for raising angiotensin levels in response to hemodynamic changes. *Raised cardiac output* - **Increased cardiac output** generally leads to **increased blood pressure**, which would suppress renin release and reduce angiotensin levels. - The body's homeostatic mechanisms aim to lower blood pressure in response to increased cardiac output, not raise angiotensin. - This has the opposite effect on the RAAS system. *Increased sympathetic tone* - While **increased sympathetic tone does stimulate renin release** via β1-adrenergic receptors on juxtaglomerular cells, it is typically a **secondary mechanism** that occurs in response to decreased blood pressure. - Sympathetic stimulation is one of three major stimuli for renin release, but in physiological terms, it usually acts as part of the compensatory response to hypotension rather than as an independent primary cause. - The question asks for the cause of raised angiotensin, and decreased blood pressure is the more direct and primary trigger. *Increased blood volume* - **Increased blood volume** results in **elevated blood pressure**, which would suppress renin release and consequently lower angiotensin levels. - Atrial natriuretic peptide (ANP) is released in response to increased blood volume, which inhibits renin secretion. - This has the opposite effect on angiotensin levels.

Renal Physiology Indian Medical PG Question 9: Which of the following is not an effect of efferent arteriole constriction:

• A. Increased glomerular hydrostatic pressure
• B. Decreased blood flow in peritubular vessels
• C. Decreased GFR (Correct Answer)
• D. Increased oncotic pressure in peritubular vessels

Renal Physiology Explanation: ***Decreased GFR*** - **Efferent arteriole constriction** typically *increases* GFR, not decreases it - Constriction raises **glomerular hydrostatic pressure** (PGC) by increasing resistance to outflow, which *enhances* the driving force for filtration - The initial and predominant effect is an **increase in GFR**, making "Decreased GFR" NOT a typical effect - Only with *severe* prolonged constriction might GFR eventually fall due to markedly reduced renal blood flow and extreme protein concentration *Increased glomerular hydrostatic pressure* - This IS an effect of efferent arteriole constriction - Constriction increases resistance to blood leaving the glomerulus, causing blood to "back up" and **raising hydrostatic pressure** in glomerular capillaries - This elevated pressure directly increases the filtration force *Decreased blood flow in peritubular vessels* - This IS an effect of efferent arteriole constriction - Blood exits the glomerulus through the efferent arteriole to reach peritubular capillaries - Constriction restricts this outflow, resulting in **reduced blood flow** to downstream peritubular vessels *Increased oncotic pressure in peritubular vessels* - This IS an effect of efferent arteriole constriction - As filtration increases due to higher glomerular pressure, plasma proteins (which cannot be filtered) become more concentrated in the blood - This concentrated blood flows into peritubular capillaries, resulting in **elevated oncotic pressure** that favors reabsorption

Renal Physiology Indian Medical PG Question 10: A hyperventilating patient has the following ABG values: pH=7.53, pCO2=20 mmHg, HCO3= 26 mEq/L. What is the most likely diagnosis?

• A. Metabolic alkalosis
• B. Metabolic acidosis
• C. Respiratory alkalosis (Correct Answer)
• D. Respiratory acidosis

Renal Physiology Explanation: ***Respiratory alkalosis*** - The pH of 7.53 indicates **alkalemia**, and the low pCO2 (20 mmHg) is the primary driver, signifying **respiratory alkalosis** - A hyperventilating patient exhales more CO2, leading to a decrease in its partial pressure in the blood and a subsequent rise in pH - The HCO3 is within normal range (26 mEq/L), indicating **uncompensated respiratory alkalosis** *Metabolic alkalosis* - This would be characterized by a high pH and an elevated **HCO3**, but the HCO3 is within the normal range (26 mEq/L) - While it causes alkalemia, the primary disturbance here is respiratory, not metabolic *Metabolic acidosis* - This would present with a **low pH** and a low **HCO3**, which is contrary to the given ABG values - The patient's pH is elevated, indicating an alkalotic state, not acidotic *Respiratory acidosis* - This would be defined by a **low pH** and an elevated **pCO2**, which is the exact opposite of the provided ABG results - The patient's high pH and low pCO2 rule out respiratory acidosis

Renal Physiology Flashcard 1 of 10

Question: In the inner medullary collecting ducts, urea is reabsorbed by the _____ transporter, which is activated by ADH

Answer: UT1

Renal Physiology Flashcard 2 of 10

Question: In the presence of _____, aquaporin 2 channels are inserted in the luminal membrane of principal cells of the late distal tubule and collecting duct

Answer: ADH

Renal Physiology Flashcard 3 of 10

Question: PCT cells are involved in sustaining _____ which increases solute and water reabsorption in response to increased GFR.

Answer: glomerulotubular balance

Renal Physiology Flashcard 4 of 10

Question: An _____ in the filtration fraction is associated with a decrease in the Glomerular Filtration Rate.

Answer: increase

Renal Physiology Flashcard 5 of 10

Question: The _____ is the site of action of loop diuretics

Answer: thick ascending limb (of Henle)

Renal Physiology Flashcard 6 of 10

Question: When CH2O is _____, urine is hypo-osmotic relative to plasma

Answer: positive

Renal Physiology Flashcard 7 of 10

Question: In the absence of _____, the principal cells of the late distal tubule and collecting duct are impermeable to water

Answer: ADH

Renal Physiology Flashcard 8 of 10

Question: The major solutes absorbed in the proximal tubule are _____ and NaHCO3

Answer: NaCl

Renal Physiology Flashcard 9 of 10

Question: The _____ cells of the late distal tubule and collecting duct secrete K+

Answer: principal

Renal Physiology Flashcard 10 of 10

Question: What formula is used to calculate clearance? _____

Answer: