Renal Regulation of Acid-Base Balance Indian Medical PG Practice Questions and MCQs
Practice Indian Medical PG questions for Renal Regulation of Acid-Base Balance. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Renal Regulation of Acid-Base Balance Indian Medical PG Question 1: Mechanism of secretion of ammonia in distal tubule is?
- A. Primary active transport
- B. Symport
- C. Antiport
- D. Passive diffusion (Correct Answer)
Renal Regulation of Acid-Base Balance Explanation: ***Passive diffusion***
- Ammonia (NH3) is a **lipid-soluble molecule** that can readily cross cell membranes, including those of the distal tubule and collecting duct, down its **concentration gradient**.
- This process is crucial for regulating **acid-base balance**, as NH3 traps H+ ions to form NH4+, which is then excreted.
*Primary active transport*
- This mechanism involves the direct use of **ATP hydrolysis** to move ions against their concentration gradient, which is not the primary way ammonia is secreted in the distal tubule.
- While NH4+ can be secreted via active transport in some segments (e.g., substituting for K+ on the Na-K-2Cl cotransporter in the thick ascending limb), free ammonia diffusion is distinct.
*Symport*
- **Symport** involves the co-transport of two or more different molecules or ions in the same direction across a cell membrane, powered by an electrochemical gradient.
- This mechanism is not typically involved in the secretion of uncharged, lipid-soluble ammonia.
*Antiport*
- **Antiport** is a type of coupled transport where two different ions or molecules move in opposite directions across a membrane.
- While antiport systems are essential for various renal functions (e.g., Na+/H+ exchanger), they are not the primary mechanism for the secretion of free ammonia in the distal tubule.
Renal Regulation of Acid-Base Balance Indian Medical PG Question 2: Maximum absorption of HCO3- occurs in:
- A. DCT
- B. PCT (Correct Answer)
- C. collecting duct
- D. ascending limb of the loop of Henle
Renal Regulation of Acid-Base Balance Explanation: ***PCT***
- The **proximal convoluted tubule (PCT)** reabsorbs approximately **80-90% of filtered bicarbonate (HCO3-)** from the glomerular filtrate.
- This high reabsorption rate is crucial for **maintaining acid-base balance** and preventing bicarbonate loss in urine.
*DCT*
- The **distal convoluted tubule (DCT)** reabsorbs a much smaller percentage of bicarbonate compared to the PCT.
- Its primary role in acid-base balance is often related to **acid secretion** rather than bulk bicarbonate reabsorption.
*collecting duct*
- The **collecting duct** plays a significant role in the *final regulation* of acid-base balance, including variable bicarbonate reabsorption or secretion, but not the majority of absorption.
- Its bicarbonate handling is influenced by the body's acid-base status, with **intercalated cells** being key players.
*ascending limb of the loop of Henle*
- The **thick ascending limb of the loop of Henle** is primarily responsible for the reabsorption of **sodium, potassium, and chloride** (via the NKCC2 co-transporter).
- It has **minimal to no direct reabsorption of bicarbonate**, making it an unlikely site for maximum HCO3- absorption.
Renal Regulation of Acid-Base Balance Indian Medical PG Question 3: What is the most common cause of normal anion gap metabolic acidosis?
- A. Ingestion of ammonium chloride
- B. Lactic acidosis
- C. Ethylene glycol intoxication
- D. Renal tubular acidosis
- E. Salicylate intoxication
- F. External pancreatic drainage
- . Diarrhoea (Correct Answer)
- . Chronic renal failure
- . Methanol/Formaldehyde intoxication
- . Uterosigmoidostomy
- . Ketoacidosis
Renal Regulation of Acid-Base Balance Explanation: ***Diarrhoea***
- Diarrhoea causes a **loss of bicarbonate** from the gastrointestinal tract, leading to a **normal anion gap metabolic acidosis** [2].
- The loss of bicarbonate is compensated by an **increase in chloride reabsorption** in the kidneys, maintaining a normal anion gap.
*Ingestion of ammonium chloride*
- Ingestion of ammonium chloride leads to **hyperchloremic metabolic acidosis** by contributing to a net gain of hydrogen ions.
- While it causes a normal anion gap metabolic acidosis, it is **not the most common cause** in clinical practice.
*Lactic acidosis*
- Lactic acidosis results from the accumulation of **lactic acid**, an unmeasured anion, leading to a **high anion gap metabolic acidosis** [1].
- This typically occurs in conditions of **tissue hypoxia** or impaired lactate metabolism [1].
*Ethylene glycol intoxication*
- Ethylene glycol metabolism produces various organic acids (e.g., **glycolic acid, oxalic acid**), which are unmeasured anions, causing a **high anion gap metabolic acidosis**.
- It is often associated with acute **kidney injury** and neurological symptoms.
*Renal tubular acidosis*
- Renal tubular acidosis (RTA) involves impaired acid excretion or bicarbonate reabsorption by the kidneys, resulting in a **normal anion gap metabolic acidosis** [1].
- While a significant cause, it is **less common globally** than diarrhoea as a cause of normal anion gap metabolic acidosis.
*Salicylate intoxication*
- Salicylate intoxication initially causes **respiratory alkalosis** due to central respiratory stimulation [1].
- At toxic levels, it can lead to **high anion gap metabolic acidosis** due to the accumulation of organic acids and uncoupling of oxidative phosphorylation.
*External pancreatic drainage*
- External pancreatic drainage can lead to significant **bicarbonate loss**, as pancreatic fluid is rich in bicarbonate.
- This loss causes a **normal anion gap metabolic acidosis**, similar to severe diarrhoea.
*Chronic renal failure*
- Chronic renal failure can cause metabolic acidosis, but it's typically a **high anion gap metabolic acidosis** due to the accumulation of unexcreted organic acids (e.g., phosphates, sulfates).
- In earlier stages, or when accompanied by specific renal tubular defects, it can sometimes present as normal anion gap acidosis.
*Methanol/Formaldehyde intoxication*
- Methanol and formaldehyde intoxication lead to **high anion gap metabolic acidosis** due to their metabolism into highly toxic substances like **formic acid**.
- These are characterized by severe systemic toxicity and visual disturbances.
*Uterosigmoidostomy*
- Uterosigmoidostomy involves diverting urine into the sigmoid colon, allowing for the reabsorption of **chloride** and the loss of **bicarbonate** from the body.
- This results in a **normal anion gap metabolic acidosis**, also known as **hyperchloremic metabolic acidosis**.
*Ketoacidosis*
- Ketoacidosis (e.g., diabetic ketoacidosis, alcoholic ketoacidosis) is characterized by the overproduction of **ketoacids** (beta-hydroxybutyrate, acetoacetate).
- These are unmeasured anions, leading to a prominent **high anion gap metabolic acidosis**.
Renal Regulation of Acid-Base Balance Indian Medical PG Question 4: Aldosterone mainly acts upon
- A. Loop of Henle
- B. Distal renal tubule (Correct Answer)
- C. PCT
- D. Glomerulus
Renal Regulation of Acid-Base Balance Explanation: ***Distal renal tubule***
- Aldosterone primarily acts on the **principal cells** of the **distal convoluted tubule** and collecting duct.
- Its main function is to promote **sodium reabsorption** and **potassium excretion** in these segments.
*Loop of Henle*
- The Loop of Henle is primarily involved in establishing the **medullary osmotic gradient** and reabsorbing water and solutes, but it is **not the primary site** of aldosterone action.
- While some sodium is reabsorbed here, this process is largely independent of aldosterone's direct influence.
*PCT*
- The **proximal convoluted tubule (PCT)** is responsible for the bulk reabsorption of filtered substances, including about 65% of sodium and water.
- Aldosterone has **minimal to no direct effect** on the reabsorptive processes occurring in the PCT.
*Glomerulus*
- The **glomerulus** is the site of **ultrafiltration**, where blood is filtered to form a protein-free filtrate.
- Aldosterone has no direct action on the filtration barrier or the cells of the glomerulus.
Renal Regulation of Acid-Base Balance Indian Medical PG Question 5: Aldosterone acts chiefly on which of the following parts of the nephron:
- A. DCT (Correct Answer)
- B. Glomerulus
- C. Loop of Henle
- D. PCT
Renal Regulation of Acid-Base Balance Explanation: ***DCT***
- Aldosterone primarily acts on the **principal cells** in the **distal convoluted tubule (DCT)** and collecting duct.
- Its main roles are increasing **sodium reabsorption** and **potassium secretion** from the tubular fluid.
*Glomerulus*
- The glomerulus is responsible for **filtration** of blood, not hormonal regulation of electrolyte reabsorption.
- It is where the initial filtrate is formed, based on pressure gradients.
*Loop of Henle*
- The Loop of Henle is crucial for establishing the **medullary osmotic gradient**, primarily through reabsorption of water (descending limb) and solutes (ascending limb).
- It does not have significant receptors for aldosterone regulation.
*PCT*
- The proximal convoluted tubule (PCT) is the primary site for the **non-regulated reabsorption** of most filtered solutes, including a large percentage of sodium, glucose, and amino acids.
- Its reabsorptive functions are largely independent of aldosterone.
Renal Regulation of Acid-Base Balance Indian Medical PG Question 6: Among the following conditions, which is most likely to cause type 4 renal tubular acidosis?
- A. Chronic pyelonephritis
- B. Diabetic nephropathy (Correct Answer)
- C. Systemic lupus
- D. Multiple myeloma
Renal Regulation of Acid-Base Balance Explanation: ***Diabetic nephropathy***
- **Diabetic nephropathy** is a common cause of **type 4 renal tubular acidosis (RTA)** due to damage to the **juxtaglomerular apparatus** affecting **renin production** and subsequent aldosterone levels.
- The resulting **hypoaldosteronism** or **aldosterone resistance** [1] leads to impaired potassium and hydrogen secretion in the **distal tubules**, causing **hyperkalemia** and **metabolic acidosis**. [1]
*Chronic pyelonephritis*
- While chronic pyelonephritis can lead to **renal scarring** and **chronic kidney disease**, it typically does not directly cause type 4 RTA.
- It is more commonly associated with a variety of tubular defects, but not specifically the **hypoaldosteronism** characteristic of type 4 RTA unless severe general renal failure is present.
*Systemic lupus*
- **Systemic lupus erythematosus (SLE)** can cause **lupus nephritis**, leading to various forms of kidney damage, but it is more commonly associated with **type 1 (distal)** or **type 2 (proximal) RTA**, rather than type 4.
- Type 1 RTA in SLE is often due to an **autoimmune attack** on the **distal tubule's ability** to secrete hydrogen ions.
*Multiple myeloma*
- **Multiple myeloma** is known to cause **renal impairment** primarily through the deposition of **light chains** in the tubules, often leading to **proximal tubular dysfunction** (Fanconi syndrome) or **cast nephropathy**.
- This typically results in **type 2 RTA** (proximal RTA) characterized by impaired reabsorption of bicarbonate, amino acids, and phosphate, rather than the distal tubular and aldosterone-related issues seen in type 4 RTA.
Renal Regulation of Acid-Base Balance Indian Medical PG Question 7: In plasma, if pH is 5, what is the fraction of base to acid?
- A. 0.01
- B. 0.1 (Correct Answer)
- C. 1
- D. 10
Renal Regulation of Acid-Base Balance Explanation: ***0.1***
- This question applies the **Henderson-Hasselbalch equation**: pH = pKa + log([base]/[acid]). For the **bicarbonate buffer system** (the primary plasma buffer), pKa ≈ 6.1.
- Substituting the given values: $5 = 6.1 + \log([HCO_3^-] / [H_2CO_3])$
- Rearranging: $\log([HCO_3^-] / [H_2CO_3]) = 5 - 6.1 = -1.1$
- Therefore: $[HCO_3^-] / [H_2CO_3] = 10^{-1.1} ≈ 0.079$
- Among the given options, **0.079 is closest to 0.1**, making this the correct answer.
- Note: pH 5 in plasma is physiologically impossible (incompatible with life), but this tests theoretical understanding of the buffer equation.
*0.01*
- This ratio would correspond to an even **more acidic** condition with $\log([base]/[acid]) = -2$.
- Using Henderson-Hasselbalch: pH = 6.1 + (-2) = 4.1, which is lower than the given pH of 5.
- The calculated ratio of 0.079 is much closer to 0.1 than to 0.01.
*1*
- A ratio of 1 means **equal concentrations** of base and acid, which occurs when pH = pKa.
- This would give pH = 6.1, not the given pH of 5.
- This represents a **neutral buffer condition**, not the acidic state described.
*10*
- This ratio indicates an **alkaline** solution with 10 times more base than acid.
- Using Henderson-Hasselbalch: pH = 6.1 + log(10) = 6.1 + 1 = 7.1 (physiological alkalosis).
- This contradicts the given acidic pH of 5.
Renal Regulation of Acid-Base Balance Indian Medical PG Question 8: Which one of the following biochemical abnormalities can be produced by repeated vomiting?
- A. Metabolic acidosis
- B. Metabolic alkalosis (Correct Answer)
- C. Ketosis
- D. Uraemia
Renal Regulation of Acid-Base Balance Explanation: ***Metabolic alkalosis***
- Repeated vomiting leads to the loss of **hydrochloric acid (HCl)** from the stomach, causing **hypochloremic metabolic alkalosis** with an increase in serum **bicarbonate (HCO3-)** and a rise in blood pH.
- The loss of H+ and Cl- ions results in **compensatory hypokalemia** as the kidneys exchange K+ for H+ to maintain electroneutrality.
- **Volume depletion** from vomiting triggers aldosterone secretion, which further promotes K+ loss and H+ excretion, perpetuating the alkalosis (contraction alkalosis).
- This is one of the most common causes of metabolic alkalosis in clinical practice.
*Metabolic acidosis*
- This condition is characterized by a decrease in **serum pH** and **bicarbonate levels**, typically due to excess acid production or bicarbonate loss from diarrhea or renal tubular acidosis.
- Vomiting does not directly cause metabolic acidosis; rather, it leads to the opposite effect by removing acidic gastric contents.
*Ketosis*
- **Ketosis** occurs when the body metabolizes fat for energy, producing **ketone bodies**, common in conditions like uncontrolled diabetes or prolonged starvation.
- While severe, prolonged vomiting with reduced oral intake can indirectly lead to starvation ketosis, the primary and most characteristic biochemical abnormality of repeated vomiting is metabolic alkalosis, not ketosis.
*Uraemia*
- **Uraemia** is a syndrome caused by the accumulation of **nitrogenous waste products** (urea, creatinine) in the blood, primarily due to kidney failure.
- Vomiting may be a *symptom* of uraemia, but it does not *cause* uraemia. Kidney function is the primary determinant of urea levels.
Renal Regulation of Acid-Base Balance Indian Medical PG Question 9: Carbonic anhydrase activity is found in all of the following except?
- A. Brain
- B. Kidney
- C. RBC
- D. Plasma (Correct Answer)
Renal Regulation of Acid-Base Balance Explanation: ***Plasma***
- **Carbonic anhydrase** is an intracellular enzyme that catalyzes the rapid interconversion of carbon dioxide and water to carbonic acid, **bicarbonate**, and protons.
- It is notably **absent in plasma** in healthy individuals, as it is primarily found within cells where its function is crucial for pH regulation and CO2 transport.
*Brain*
- Carbonic anhydrase is found in various brain cells, including **neurons**, **oligodendrocytes**, and **astrocytes**.
- It plays a vital role in pH regulation, fluid balance, and the production of cerebrospinal fluid (CSF) within the **central nervous system**.
*Kidney*
- The kidney is rich in carbonic anhydrase, particularly in the **proximal tubules** and collecting ducts.
- It is critical for **bicarbonate reabsorption** and proton excretion, essential processes for maintaining acid-base balance.
*RBC*
- **Red blood cells (RBCs)** contain a high concentration of carbonic anhydrase (specifically CA-I and CA-II isoforms).
- This enzyme facilitates the rapid conversion of CO2 to bicarbonate for transport to the lungs and the reverse reaction for **CO2 exhalation**.
Renal Regulation of Acid-Base Balance Indian Medical PG Question 10: In a comatose patient with a blood glucose level of 750 mg/dL, which test is most important to perform in addition to serum potassium?
- A. Serum creatinine
- B. Serum sodium
- C. Serum ketones
- D. Arterial blood gases (Correct Answer)
Renal Regulation of Acid-Base Balance Explanation: ***Arterial blood gases***
- In a comatose patient with severe hyperglycemia (750 mg/dL), **arterial blood gases (ABGs)** are crucial to assess for **acidosis**, which could indicate **diabetic ketoacidosis (DKA)** or **hyperosmolar hyperglycemic state (HHS)** with lactic acidosis [1], [4].
- The **pH**, **bicarbonate (HCO3-)**, and **pCO2** levels from ABGs help determine the severity and type of metabolic derangement, guiding immediate treatment, especially for potential **cerebral edema** [3], [4].
*Serum creatinine*
- While important for assessing **kidney function** in hyperosmolar states, it does not directly evaluate the immediate acid-base status that is critical for neurologic function in a comatose patient.
- Renal insufficiency can exacerbate electrolyte imbalances and fluid overload but is secondary to the immediate need for acid-base assessment.
*Serum sodium*
- **Serum sodium** is important for calculating **effective serum osmolality**, which is elevated in both DKA and HHS, contributing to mental status changes [2].
- However, while important, it does not provide information about the **acid-base balance**, which is a more critical determinant of immediate neurologic stability and treatment in deep coma.
*Serum ketones*
- **Serum ketones** are essential for distinguishing between **DKA** (high ketones) and **HHS** (low or absent ketones) [4].
- While vital for diagnosis, ketones alone do not give the full picture of **acid-base status** (pH, bicarbonate) which is directly assessed by ABGs and more immediately actionable in managing a severely ill, comatose patient [1].
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