Nitrogen Balance — MCQs
Protein metabolism after trauma is characterized by the following except:
Positive nitrogen balance is seen in -
In starvation, nitrogen is primarily carried from muscle to liver and kidney by which amino acid?
Acid-base imbalance is suspected in a patient. Which of the following parameters would you use for initial determination of acid-base status?
Glutamine is increased in CSF, blood & urine WITHOUT elevated orotic acid in which defect:
What is the Net Protein Utilization (NPU) for eggs?
Assertion: In a patient with chronic kidney disease (CKD) and metabolic acidosis, sodium bicarbonate should be initiated to correct acidosis. Reason: Sodium bicarbonate therapy reduces the progression of kidney disease by decreasing tubular injury and slowing fibrosis.
Calculate net filtration pressure with the following data: PGC = 42 mm Hg, πGC = 12 mm Hg, PBC = 16 mm Hg. Assume that no proteins were filtered.
A 32-year-old male is on a weight-maintenance diet, so he does not want to lose or gain any weight. Which amino acid must be present in the diet to prevent the patient from going into a negative nitrogen balance?
For the conversion of aspartate to asparagine, nitrogen comes from which source?
Nitrogen Balance Indian Medical PG Practice Questions and MCQs
Question 1: Protein metabolism after trauma is characterized by the following except:
- A. Increased liver gluconeogenesis
- B. Increased urinary nitrogen loss
- C. Hepatic synthesis of acute phase reactants
- D. Inhibition of skeletal muscle breakdown by interleukin 1 and tumour necrosis factor (Correct Answer)
Explanation: ***Inhibition of skeletal muscle breakdown by interleukin 1 and tumour necrosis factor*** - After trauma, **interleukin 1 (IL-1)** and **tumor necrosis factor (TNF)** actually **promote** skeletal muscle breakdown (catabolism) to provide amino acids for gluconeogenesis and acute phase protein synthesis. - This statement is incorrect because these cytokines are **pro-catabolic**, not inhibitory, in their effect on muscle protein. *Increased liver gluconeogenesis* - Trauma leads to a significant increase in **liver gluconeogenesis**, primarily to maintain glucose supply for **immune cells** and wound healing, which rely heavily on glucose. - This process utilizes amino acids obtained from muscle breakdown as substrates. *Increased urinary nitrogen loss* - The breakdown of muscle protein releases amino acids, which are then deaminated. The nitrogen waste product, **urea**, is excreted in the urine, leading to **increased urinary nitrogen loss**. - This is a direct consequence of the catabolic state. *Hepatic synthesis of acute phase reactants* - The liver increases the synthesis of **acute phase reactants** (e.g., C-reactive protein, fibrinogen, haptoglobin) in response to inflammatory cytokines like IL-1, **IL-6**, and TNF. - These proteins play a crucial role in the inflammatory response and tissue repair.
Question 2: Positive nitrogen balance is seen in -
- A. Scurvy
- B. Growing children (Correct Answer)
- C. Osteomalacia
- D. Acute illness
Explanation: ***Growing children*** - **Positive nitrogen balance** occurs when nitrogen intake (from protein) exceeds nitrogen excretion, indicating net protein synthesis and tissue anabolism. - This state is essential for **growth and development** as children build new tissues like muscle, bone, and organs, requiring more protein synthesis than breakdown. *Scurvy* - Scurvy is a disease caused by **vitamin C deficiency**, which is crucial for collagen synthesis. - It leads to impaired wound healing, weakened connective tissue, and is not directly associated with positive nitrogen balance. *Osteomalacia* - Osteomalacia is characterized by **softening of bones** due to impaired mineralization, often caused by **vitamin D deficiency**. - It relates to bone metabolism rather than overall protein synthesis or nitrogen balance. *Acute illness* - Acute illness, especially severe illness or trauma, typically leads to a **negative nitrogen balance**. - This occurs due to increased **catabolism** (protein breakdown) to provide energy and amino acids for the acute stress response and inflammation.
Question 3: In starvation, nitrogen is primarily carried from muscle to liver and kidney by which amino acid?
- A. Alanine (Correct Answer)
- B. Glycine
- C. Aspartic acid
- D. Asparagine
Explanation: ***Alanine*** - During starvation, muscles break down proteins, and the amino groups from these proteins are transferred to **pyruvate** to form **alanine** via the **glucose-alanine cycle (Cahill cycle)**. - **Alanine** is then released into the bloodstream and transported primarily to the **liver**, where its carbon skeleton can be used for **gluconeogenesis** and the amino group enters the urea cycle. - Note: While alanine is the primary carrier to the liver, **glutamine** is the main nitrogen carrier to the kidney. However, among the given options, alanine is unequivocally the correct answer. *Aspartic acid* - While aspartate is involved in amino group transfer and is a crucial component of the **urea cycle**, it is not the primary carrier for inter-organ nitrogen transport from muscle to liver during starvation. - Its role is more localized within the liver for the urea cycle rather than as a transport amino acid. *Glycine* - Glycine plays roles in various metabolic pathways, including synthesis of heme, purines, and conjugation reactions, but it is not the primary amino acid for carrying nitrogen from muscle to liver during starvation. - Its small size and simple structure make it less suitable for efficient nitrogen transport compared to alanine. *Asparagine* - Asparagine has a minor role in nitrogen transport but is not the primary carrier during starvation. - It is synthesized from **aspartate** and ammonia and is typically involved in protein synthesis and nitrogen storage in some tissues.
Question 4: Acid-base imbalance is suspected in a patient. Which of the following parameters would you use for initial determination of acid-base status?
- A. pH, PaCO2, and Base excess
- B. pH, PaCO2, and Bicarbonate (Correct Answer)
- C. pH and PaCO2
- D. pH, PaCO2, Bicarbonate, and Base excess
Explanation: ***pH, PaCO2, and Bicarbonate*** - The **pH** provides immediate assessment of overall acid-base status (acidemia if <7.35 or alkalemia if >7.45) - The **PaCO2** reflects the respiratory component - elevated in respiratory acidosis or compensated metabolic alkalosis; decreased in respiratory alkalosis or compensated metabolic acidosis - The **HCO3- (bicarbonate)** reflects the metabolic component - essential for determining whether the primary disorder is metabolic or respiratory - This triad forms the **standard approach** to arterial blood gas (ABG) interpretation taught in all major medical textbooks - Together, these three parameters allow complete initial classification of acid-base disorders using the Henderson-Hasselbalch relationship *pH and PaCO2* - While pH and PaCO2 are critical measurements, **without bicarbonate**, you cannot differentiate between metabolic and respiratory disorders or assess metabolic compensation - For example, a low pH with normal PaCO2 could indicate metabolic acidosis, but you need HCO3- to confirm this diagnosis - Incomplete for initial acid-base determination *pH, PaCO2, and Base excess* - Base excess is a **calculated parameter** used to quantify the metabolic component of acid-base disturbances - While useful, it is considered a **secondary parameter** for more detailed metabolic analysis rather than essential for initial determination - Standard ABG interpretation uses bicarbonate, not base excess, as the primary metabolic parameter *pH, PaCO2, Bicarbonate, and Base excess* - While this includes all relevant parameters, **base excess is redundant** for initial determination - Base excess adds quantitative information about metabolic component but is not required for the initial classification of acid-base status - The essential triad for initial assessment is pH, PaCO2, and HCO3-
Question 5: Glutamine is increased in CSF, blood & urine WITHOUT elevated orotic acid in which defect:
- A. Arginase
- B. Argininosuccinate lyase deficiency
- C. CPS-I (Correct Answer)
- D. Arginosuccinate synthetase
- E. OTC
Explanation: ***CPS-I*** - A deficiency in **Carbamoyl Phosphate Synthetase I (CPS-I)** leads to a severe block in the **urea cycle**, resulting in profound hyperammonemia. - The elevated ammonia is then shunted to produce more **glutamine** (via glutamine synthetase), which serves as a detoxification mechanism but also causes high levels of glutamine in CSF, blood, and urine. *Arginase* - **Arginase deficiency** primarily leads to elevated **arginine** levels and mild to moderate hyperammonemia, but not typically a dramatic increase in glutamine due to the block occurring later in the cycle. - Clinical features include progressive spasticity, growth retardation, and intellectual disability. *Argininosuccinate lyase deficiency* - This deficiency causes accumulation of **argininosuccinate** in body fluids, which is a diagnostic marker, rather than primarily increased glutamine. - It presents with severe hyperammonemia, neurological symptoms, and often hepatomegaly. *Arginosuccinate synthetase* - A deficiency in **argininosuccinate synthetase** (also known as citrullinemia type I) leads to a buildup of **citrulline** and severe hyperammonemia. - While hyperammonemia can indirectly increase glutamine, the primary diagnostic marker is elevated citrulline, and the glutamine increase is not as pronounced or directly symptomatic as in CPS-I deficiency. *OTC* - **Ornithine Transcarbamylase (OTC) deficiency** is the most common urea cycle disorder and leads to severe hyperammonemia, accompanied by elevated **orotic acid** due to carbamoyl phosphate shunting to pyrimidine synthesis. - While hyperammonemia drives glutamine synthesis, the presence of elevated orotic acid is a key differentiator from CPS-I deficiency, which does not have increased orotic acid.
Question 6: What is the Net Protein Utilization (NPU) for eggs?
- A. 70
- B. 80
- C. 94 (Correct Answer)
- D. 100
Explanation: ***94*** - **Eggs** are considered a **high-quality protein source** with a Net Protein Utilization (NPU) of approximately **94**, indicating very efficient protein absorption and utilization by the body. - This high NPU reflects the excellent balance of **essential amino acids** in eggs, making them a benchmark for protein quality. *70* - An NPU of 70 is generally considered good but is lower than that of **eggs**, which are among the most efficiently utilized proteins. - This value might be typical for some **plant-based proteins** or mixtures of proteins with slightly less optimal essential amino acid profiles. *80* - An NPU of 80 indicates good protein quality but is still significantly lower than the **NPU of eggs**. - This value is often seen in high-quality **meat proteins** or well-balanced **dairy products**. *100* - An NPU of 100 would mean that all ingested protein is perfectly absorbed and utilized by the body without any loss, which is **theoretically impossible** for biological systems. - While some protein quality metrics might approach 100, **NPU is a measure of actual utilization** and never reaches 100 due to metabolic losses.
Question 7: Assertion: In a patient with chronic kidney disease (CKD) and metabolic acidosis, sodium bicarbonate should be initiated to correct acidosis. Reason: Sodium bicarbonate therapy reduces the progression of kidney disease by decreasing tubular injury and slowing fibrosis.
- A. Assertion is false, but Reason is true
- B. Both Assertion and Reason are true, and Reason is the correct explanation of Assertion
- C. Assertion is true, but Reason is false
- D. Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion (Correct Answer)
Explanation: The **Assertion** is true: **KDIGO guidelines** recommend sodium bicarbonate therapy for CKD patients when serum bicarbonate falls below **22 mEq/L** to correct metabolic acidosis [2]. - The **Reason** is also true: studies demonstrate that bicarbonate therapy has **nephroprotective effects**, reducing CKD progression through decreased **tubular injury** and **interstitial fibrosis**. However, this describes a secondary benefit rather than the primary indication for initiating therapy. *Both Assertion and Reason are true, and Reason is the correct explanation of Assertion* - While both statements are medically accurate, the Reason does not explain the primary indication for bicarbonate initiation in CKD patients. - The main purpose is **acid-base correction** and prevention of acidosis complications like **bone disease**, **muscle wasting**, and **cardiovascular effects**, not primarily nephroprotection [1], [2]. *Assertion is false, but Reason is true* - The Assertion is medically correct: sodium bicarbonate is **standard therapy** for metabolic acidosis in CKD according to nephrology guidelines. - CKD patients develop acidosis due to impaired **renal acid excretion** and reduced **bicarbonate regeneration**, making correction clinically necessary [2]. *Assertion is true, but Reason is false* - The Reason is actually supported by **clinical evidence**: randomized controlled trials show bicarbonate therapy slows CKD progression. - Mechanisms include reduced **complement activation**, decreased **endothelin production**, and preservation of **residual kidney function**.
Question 8: Calculate net filtration pressure with the following data: PGC = 42 mm Hg, πGC = 12 mm Hg, PBC = 16 mm Hg. Assume that no proteins were filtered.
- A. 14 mm Hg (Correct Answer)
- B. 28 mm Hg
- C. Data not sufficient
- D. 34 mm Hg
Explanation: ***14 mm Hg*** - The **net filtration pressure (NFP)** is calculated using the formula: **NFP = (PGC - PBC) - πGC**. - Plugging in the given values: (42 mmHg - 16 mmHg) - 12 mmHg = 26 mmHg - 12 mmHg = **14 mmHg**. *28 mm Hg* - This answer likely results from an incorrect application of the NFP formula, such as adding the oncotic pressure instead of subtracting it, or miscalculating the difference between hydrostatic pressures. - For example, if both hydrostatic and oncotic pressures were added (42 + 12 + 16), it would yield a much higher number, or if the subtraction was done incorrectly. *Data not sufficient* - All necessary variables for calculating the NFP are provided: **glomerular hydrostatic pressure (PGC)**, **glomerular oncotic pressure (πGC)**, and **Bowman's capsule hydrostatic pressure (PBC)**. - The assumption that "no proteins were filtered" simplifies the calculation, confirming that sufficient data is available. *34 mm Hg* - This result would occur if the oncotic pressure in Bowman's capsule (πBC) was incorrectly considered, or if a different formulation of the NFP calculation was used. - Given that **πBC is assumed to be zero** (as no proteins are filtered into Bowman's capsule), any calculation that leads to 34 mmHg is likely based on an error in applying the formula, such as adding **πGC** instead of subtracting it from the hydrostatic pressure difference.
Question 9: A 32-year-old male is on a weight-maintenance diet, so he does not want to lose or gain any weight. Which amino acid must be present in the diet to prevent the patient from going into a negative nitrogen balance?
- A. Alanine
- B. Arginine
- C. Glycine
- D. Threonine (Correct Answer)
Explanation: ***Threonine*** - **Threonine** is an **essential amino acid**, meaning the body cannot synthesize it and it must be obtained from the diet. - To maintain a **neutral nitrogen balance** and prevent a **negative nitrogen balance** (loss of body protein), all essential amino acids, including threonine, must be supplied in adequate amounts. *Alanine* - **Alanine** is a **non-essential amino acid**, which means the body can synthesize it from other compounds; therefore, its absence from the diet would not directly cause a negative nitrogen balance. - It plays a significant role in **gluconeogenesis** and the **glucose-alanine cycle**. *Arginine* - **Arginine** is considered a **conditionally essential amino acid**, meaning it can be synthesized by the body, but sometimes not in sufficient amounts to meet needs (e.g., during rapid growth, illness, or trauma). - Under normal weight-maintenance conditions, the body can typically synthesize enough arginine. *Glycine* - **Glycine** is a **non-essential amino acid** and is the smallest amino acid, often easily synthesized by the body. - Its presence in the diet, while important, is not critical for preventing negative nitrogen balance because the body can produce it.
Question 10: For the conversion of aspartate to asparagine, nitrogen comes from which source?
- A. Alanine
- B. Glutamate
- C. Glutamine (Correct Answer)
- D. Histidine
Explanation: ***Glutamine*** - The biosynthesis of **asparagine** from **aspartate** is catalyzed by **asparagine synthetase**. - This enzyme utilizes **ATP** and **glutamine** as the amino group donor, with glutamine being hydrolyzed to **glutamate**. *Alanine* - **Alanine** is primarily involved in the **glucose-alanine cycle** for transporting nitrogen from muscle to liver. - It does not directly donate its amino group for the synthesis of asparagine. *Glutamate* - While **glutamate** is a precursor for glutamine, it does not directly donate an amino group in the conversion of aspartate to asparagine. - Glutamate acts as a general amino group donor in many transamination reactions, but not in this specific amidation. *Histidine* - **Histidine** is an essential amino acid involved in various metabolic roles, including acting as a precursor for histamine. - It is not a donor of nitrogen for the biosynthesis of asparagine from aspartate.
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