Renal Physiology Practice Questions

Q: Where is SGLT 2 primarily found?

None of the above. **Explanation:** The correct answer is **None of the above** because **SGLT 2 (Sodium-Glucose Cotransporter 2)** is primarily and almost exclusively located in the **Kidney**, specifically in the **S1 and S2 segments of the Proximal Convoluted Tubule (PCT)** [2]. It is responsible for reabsorbing approximately 90% of the filtered glucose from the tubular fluid back into the bloodstream [1]. **Analysis of Options:** * **A. Liver:** The liver primarily utilizes **GLUT 2** (a glucose transporter) for the bidirectional movement of glucose; it does not express SGLT 2 [2]. * **B. Intestine:** The primary sodium-glucose cotransporter in the small intestine is **SGLT 1**, which is responsible for the absorption of glucose and galactose from the dietary lumen [2]. (Note: SGLT 1 is also found in the S3 segment of the renal PCT, accounting for the remaining 10% of glucose reabsorption) [2]. * **C. Spleen:** The spleen does not play a significant role in active glucose transport via SGLT proteins. **High-Yield Clinical Pearls for NEET-PG:** * **SGLT 2 Inhibitors (Gliflozins):** Drugs like Dapagliflozin and Empagliflozin inhibit SGLT 2 in the PCT, leading to glucosuria. They are used in managing Type 2 Diabetes, Heart Failure, and Chronic Kidney Disease. * **SGLT 1 vs. SGLT 2:** Remember "1" is for the Gut (and 10% Kidney), and "2" is for the Kidney (90%). * **Fanconi Syndrome:** A generalized dysfunction of the PCT where SGLT 2 function is impaired along with the reabsorption of amino acids, uric acid, and phosphates.

Q: What is the normal Transtubular potassium gradient (TTKG) in hypokalemia?

< 3-4. **Explanation:** The **Transtubular Potassium Gradient (TTKG)** is a clinical tool used to estimate the conservation of potassium in the cortical collecting duct (CCD). It reflects the activity of aldosterone and the kidney's response to potassium levels. **1. Why Option A is Correct:** In a healthy physiological state, if a patient has **hypokalemia**, the kidneys should respond by maximizing potassium reabsorption to conserve it. This results in a very low concentration of potassium in the tubular fluid relative to the plasma. A **TTKG 3-4 in the presence of hypokalemia, it suggests **renal potassium wasting** (e.g., primary hyperaldosteronism or diuretic use). **2. Why Other Options are Incorrect:** * **Options B, C, and D:** These values represent higher gradients. A TTKG **> 7-10** is considered normal in a **hyperkalemic** patient, indicating that the kidneys are appropriately secreting excess potassium. If these high values are seen during hypokalemia, it indicates an inappropriate renal loss of potassium. **Clinical Pearls for NEET-PG:** * **Formula:** $TTKG = \frac{[K^+]_{urine} / [K^+]_{plasma}}{Osm_{urine} / Osm_{plasma}}$ * **Prerequisites:** For TTKG to be accurate, the urine must be concentrated ($Osm_{urine} > Osm_{plasma}$) and urine sodium should be $> 25 \text{ mEq/L}$ to ensure adequate delivery to the distal tubule. * **High-Yield Fact:** TTKG is primarily used to differentiate between **extra-renal** (TTKG 3-4) causes of hypokalemia.

Q: What is the principal site of sodium absorption in the nephron?

Proximal convoluted tubule. **Explanation:** The **Proximal Convoluted Tubule (PCT)** is the "workhorse" of the nephron. It is the principal site of sodium reabsorption, accounting for approximately **65-70%** of the total filtered sodium load. This process is primarily driven by the basolateral Na+/K+ ATPase pump, which creates an electrochemical gradient that facilitates sodium entry from the lumen via various symporters (like SGLT-2 for glucose) and antiporters (Na+/H+ exchanger). **Analysis of Incorrect Options:** * **Loop of Henle (Thick Ascending Limb):** This segment reabsorbs about **20-25%** of filtered sodium via the **Na+-K+-2Cl- cotransporter (NKCC2)**. It is the site of action for loop diuretics like Furosemide. * **Distal Convoluted Tubule (DCT):** This segment reabsorbs only about **5-8%** of sodium through the **Na+-Cl- symporter**. It is the site of action for Thiazide diuretics. * **Collecting Duct:** This is the site of "fine-tuning" under hormonal control (Aldosterone). It reabsorbs only **2-3%** of sodium via **ENaC (Epithelial Sodium Channels)**. **High-Yield Clinical Pearls for NEET-PG:** 1. **Isosmotic Reabsorption:** In the PCT, water follows sodium passively, meaning the tubular fluid remains **isosmotic** to plasma. 2. **SGLT-2 Inhibitors:** Drugs like Dapagliflozin act on the PCT to inhibit glucose and sodium reabsorption, used in managing Diabetes Mellitus and Heart Failure. 3. **Glomerulotubular Balance:** This mechanism ensures that the percentage of solute reabsorbed in the PCT remains constant (67%) even if the Glomerular Filtration Rate (GFR) changes.

Q: All of the following statements about Renal physiology are true, except:

The kidney receives 5% of the cardiac output. **Explanation** The correct answer is **B** because the statement is factually incorrect. The kidneys are among the most highly perfused organs in the body, receiving approximately **20-25% of the total cardiac output** (roughly 1100–1200 mL/min), not 5%. This high blood flow is not required for the metabolic needs of the renal tissue itself, but rather to ensure a high Glomerular Filtration Rate (GFR) for effective regulation of body fluids and waste excretion. **Analysis of other options:** * **Option A (True):** The ascending limb of the Loop of Henle is impermeable to water but actively reabsorbs solutes (the "diluting segment"). Consequently, the fluid entering the distal convoluted tubule is always **hypoosmotic** (approx. 100 mOsm/L) relative to plasma. * **Option C (True):** GFR is regulated by the hydrostatic pressure in the glomerular capillaries. This is controlled by the tone of the **afferent arteriole** (constriction decreases GFR) and the **efferent arteriole** (constriction increases GFR, up to a point). * **Option D (True):** The glomerulus is a high-pressure capillary network formed by the branching of the **afferent arteriole**. These capillaries then coalesce to form the efferent arteriole. **High-Yield Clinical Pearls for NEET-PG:** * **Renal Fraction:** 20-25% of Cardiac Output. * **Renal Plasma Flow (RPF):** Approximately 600-700 mL/min. * **Filtration Fraction:** GFR/RPF ≈ 20%. * **Oxygen Consumption:** Despite high blood flow, the kidney has a high arteriovenous oxygen difference only in the medulla, making the renal medulla particularly susceptible to ischemic injury (Acute Tubular Necrosis).

Q: Glucose is reabsorbed in the renal tubules and transported via which of the following mechanisms?

Sodium cotransporter. **Explanation:** Glucose reabsorption in the kidney occurs primarily in the **Proximal Convoluted Tubule (PCT)**. This process is a classic example of **Secondary Active Transport**. **Why the correct answer is right:** Glucose is transported across the apical membrane of the tubular cells against its concentration gradient. This is achieved by coupling its movement with the downhill movement of Sodium ($Na^+$) ions. This mechanism is known as **Sodium-Glucose Cotransport (Symport)**. * **SGLT-2** (Sodium-Glucose Linked Transporter 2) reabsorbs ~90% of glucose in the early PCT (S1 segment). * **SGLT-1** reabsorbs the remaining ~10% in the late PCT (S3 segment). The energy for this process is indirectly provided by the $Na^+/K^+$ ATPase pump on the basolateral membrane, which maintains the low intracellular sodium concentration. **Why the incorrect options are wrong:** * **Sodium antiporter:** An antiporter (counter-transporter) moves substances in opposite directions. In the PCT, the $Na^+/H^+$ exchanger is an antiporter, but glucose moves in the *same* direction as sodium. * **Potassium antiporter/symporter:** Potassium transport in the renal tubules is generally independent of glucose reabsorption. Glucose transport is specifically linked to the sodium gradient, not potassium. **High-Yield Clinical Pearls for NEET-PG:** 1. **Renal Threshold for Glucose:** Glucose starts appearing in the urine (glycosuria) when blood glucose levels exceed **180 mg/dL**. 2. **Transport Maximum ($T_m$):** The $T_m$ for glucose is approximately **375 mg/min** in men and **300 mg/min** in women. 3. **SGLT-2 Inhibitors (e.g., Dapagliflozin):** A modern class of anti-diabetic drugs that inhibit these transporters to promote glucose excretion in urine. 4. **GLUT-2:** Once inside the cell, glucose exits the basolateral membrane into the blood via **Facilitated Diffusion** through GLUT-2 transporters.

Question 1

A 25-year-old woman presents with nausea and vomiting for 2 days. Her physical examination is normal except for a postural drop in blood pressure from 110/80 mm Hg supine to 90/80 mm Hg standing. Her serum electrolytes are sodium 130 mEq/L, potassium 3 mEq/L, chloride 90 mEq/L, bicarbonate 30 mEq/L, urea 50 mg/dL, and creatinine 0.8 mg/dL. Which of the following electrolytes is most likely to be filtered through the glomerulus but unaffected by tubular secretion?

Accepted Answer

Urea

Answer

Potassium

Answer

Sodium

Answer

Bicarbonate

Question 2

Where is SGLT 2 primarily found?

Accepted Answer

None of the above

Answer

Liver

Answer

Intestine

Answer

Spleen

Question 3

Sympathectomy of the kidney results in which of the following responses?

Accepted Answer

Increased urine output

Answer

No change to the glomerular filtration rate, nor to the urine output

Answer

Decreased urine output

Answer

Reduction of glomerular filtration rate and decreased urinary output

Question 4

Which of the following are actions of angiotensin II?

Accepted Answer

Systemic vasodilation

Answer

Systemic vasoconstriction

Answer

Renal vasodilatation

Answer

Reabsorption of Na+ in the proximal renal tubule

Question 5

What is the normal Transtubular potassium gradient (TTKG) in hypokalemia?

Accepted Answer

< 3-4

Answer

> 6-7

Answer

> 9-10

Answer

> 10-15

Question 6

What is the principal site of sodium absorption in the nephron?

Accepted Answer

Proximal convoluted tubule

Answer

Distal convoluted tubule

Answer

Loop of Henle (thick segment)

Answer

Collecting duct

Question 7

A man with diabetes insipidus has a glomerular filtration of 155 L/day. Which range most likely represents the upper limit for urine flow rate in this individual if he were not receiving treatment but had free access to water?

Accepted Answer

15 to 20 L/day

Answer

1 to 3 L/day

Answer

5 to 10 L/day

Answer

30 to 35 L/day

Question 8

What are the major functions of "P" cells present in cortical collecting ducts?

Accepted Answer

All of the above.

Answer

Sodium and water reabsorption from the lumen.

Answer

Potassium secretion into the lumen.

Answer

ADH controlled water reabsorption.

Question 9

All of the following statements about Renal physiology are true, except:

Accepted Answer

The kidney receives 5% of the cardiac output

Answer

Distal tubule always receives hypoosmotic solution

Answer

GFR is controlled by resistance in afferent and efferent arterioles

Answer

The Glomerulus receives capillaries from the afferent arteriole

Question 10

Glucose is reabsorbed in the renal tubules and transported via which of the following mechanisms?

Accepted Answer

Sodium cotransporter

Answer

Sodium antiporter

Answer

Potassium antiporter

Answer

Potassium symporter

Renal Physiology — MCQs

Renal Physiology — MCQs

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