Acid-Base and Electrolyte Balance Practice Questions

Q: Which of the following phospholipids serves as a marker of apoptosis?

Phosphatidylserine. **Explanation:** **Phosphatidylserine (PS)** is the correct answer because of its unique distribution in the cell membrane. In healthy cells, the enzyme **flippase** actively maintains PS on the **inner (cytoplasmic) leaflet** of the plasma membrane. During apoptosis, this asymmetry is lost due to the inactivation of flippase and the activation of **scramblase**. Consequently, PS "flips" to the **outer leaflet** (extracellular surface). This "PS exposure" acts as an "eat-me" signal, recognized by macrophages for phagocytosis without triggering inflammation. Clinical detection of this shift is commonly done using **Annexin V** staining in flow cytometry. **Analysis of Incorrect Options:** * **Phosphatidylinositol (A):** Primarily located on the inner leaflet, it serves as a precursor for second messengers like $IP_3$ and $DAG$ and anchors proteins via GPI linkages. It is not a marker for apoptosis. * **Phosphatidylcholine (C):** The most abundant phospholipid in the eukaryotic membrane, typically found on the outer leaflet. It serves a structural role and is not a signaling marker for cell death. * **Phosphatidylethanolamine (D):** Found mainly in the inner leaflet and involved in membrane fusion and cytokinesis, but its translocation is not the primary diagnostic marker for apoptosis. **High-Yield NEET-PG Pearls:** * **Annexin V:** A protein that binds specifically to Phosphatidylserine in the presence of $Ca^{2+}$; used to identify early apoptotic cells. * **Flippase vs. Scramblase:** Flippase (ATP-dependent) moves PS inward; Scramblase (Ca-activated) moves phospholipids non-specifically in both directions. * **Cardiolipin:** A phospholipid found exclusively in the inner mitochondrial membrane; its oxidation is also linked to the intrinsic pathway of apoptosis.

Q: In metabolic alkalosis, which statement is true about urinary excretion?

Decreased excretion of ammonia. ### Explanation **Core Concept:** In metabolic alkalosis, the body’s primary goal is to conserve hydrogen ions ($H^+$) and excrete excess bicarbonate ($HCO_3^-$) to restore a normal pH. The kidneys achieve this by reducing the secretion of $H^+$ into the tubular lumen. Since the formation and excretion of **ammonia ($NH_3$)** and **ammonium ($NH_4^+$)** are directly dependent on the availability of $H^+$ ions in the tubular fluid (to "trap" ammonia as ammonium), a state of alkalosis leads to a significant **decrease in renal ammoniagenesis** and ammonia excretion. **Analysis of Options:** * **D (Correct):** As $H^+$ secretion decreases during alkalosis, the conversion of $NH_3$ to $NH_4^+$ in the distal tubule diminishes, leading to decreased urinary ammonia excretion. * **A (Incorrect):** Increased $NH_3$ excretion is a hallmark of **metabolic acidosis**, where the kidneys ramp up ammonia production to buffer and eliminate excess acid. * **B & C (Incorrect):** Aceto-acetic acid and beta-hydroxybutyric acid are **ketoacids**. Their presence in urine (ketonuria) is associated with metabolic **acidosis** (e.g., Diabetic Ketoacidosis or starvation), not alkalosis. In alkalosis, the body is not in a state of pathological ketoacid production. **Clinical Pearls for NEET-PG:** * **Ammoniagenesis:** Occurs primarily in the **proximal convoluted tubule (PCT)** via the deamination of **Glutamine**. * **Urine pH:** In metabolic alkalosis, the urine is typically **alkaline** (pH > 7.0) as the kidney dumps $HCO_3^-$. * **Paradoxical Aciduria:** A high-yield exception where a patient has metabolic alkalosis but excretes acidic urine. This occurs in **hypokalemic, hypochloremic metabolic alkalosis** (e.g., persistent vomiting) because the kidney prioritizes volume and sodium conservation over pH balance.

Q: Which of the following amino acids primarily acts as a buffer in blood due to its ability to accept and donate protons at physiological pH?

Histidine. ***Histidine***- The side chain of **histidine**, the **imidazole group**, has a pKa of approximately 6.0, which is close to the physiological pH of **7.4**, making it an effective buffer.- This property is especially vital for the **buffering capacity of hemoglobin** in red blood cells, contributing significantly to pH homeostasis (Bohr effect).*Arginine*- Arginine possesses a **guanidinium group** in its side chain with a very high pKa (~12.5).- This high pKa means its side chain is almost always positively charged and protonated at physiological pH, rendering it ineffective as a physiological **acid-base buffer**.*Tryptophan*- Tryptophan has a large, non-polar **indole ring** side chain, which is chemically inert and lacks an ionizable group within the physiological pH range.- Since it cannot accept or donate protons near pH 7.4, it does not contribute to the **buffering system** of the blood.*Tyrosine*- Tyrosine contains a **phenolic hydroxyl group** with a pKa of approximately 10.5.- Because its pKa is significantly higher than physiological pH, it is largely neutral and incapable of mediating proton exchange effectively in the **blood plasma**.

Q: The following reaction occurs in which part of kidney?

Proximal convoluted tubule. **Proximal convoluted tubule** - The image shows the conversion of 25-hydroxycholecalciferol to **1,25 (OH)₂-D₃**, also known as calcitriol, via the enzyme **1α-hydroxylase**. - This critical hydroxylation reaction, occurring primarily in the **proximal convoluted tubule** cells of the kidney, produces the biologically active form of vitamin D. *Distal convoluted tubule* - The distal convoluted tubule is primarily involved in **fine-tuning** water and electrolyte reabsorption, influenced by hormones like aldosterone and antidiuretic hormone. - It does not contain the necessary enzymes, specifically **1α-hydroxylase**, for the final activation step of vitamin D. *Loop of Henle* - The loop of Henle's main function is to create a **medullary osmotic gradient** through countercurrent multiplication, crucial for concentrating urine. - It plays no significant role in the **hydroxylation of vitamin D** precursors. *Collecting duct* - The collecting duct is responsible for final adjustments to urine volume and concentration, largely under the influence of **antidiuretic hormone**. - It lacks the **enzymatic machinery** (1α-hydroxylase) required for the activation of vitamin D.

Q: Which one of the following biochemical abnormalities can be produced by repeated vomiting?

Metabolic alkalosis. ***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.

Q: Maximum buffering capacity at physiological pH is for:

Histidine. ***Correct Option: Histidine*** - Histidine possesses an **imidazole side chain** with a pKa value of approximately 6.0-6.5, which is close to the physiological pH of 7.4 - Maximum buffering capacity occurs when **pH ≈ pKa** (Henderson-Hasselbalch principle) - This proximity of its pKa to physiological pH allows histidine to effectively **accept and donate protons** as pH changes, providing the strongest buffering capacity among amino acids - Histidine residues are critical in **hemoglobin buffering** and protein buffer systems *Incorrect Option: Glycine* - Glycine's pKa values are around 2.3 for the carboxyl group and 9.6 for the amino group - Neither pKa value is close to **physiological pH 7.4**, making it a poor buffer at this pH - It lacks a side chain with a pKa near neutral pH to provide significant buffering capacity *Incorrect Option: Valine* - Valine has a **nonpolar aliphatic side chain** that does not ionize - Only the α-amino (pKa ~9.6) and α-carboxyl groups (pKa ~2.3) can buffer, both far from physiological pH - Provides minimal buffering capacity at **pH 7.4** *Incorrect Option: Cysteine* - Cysteine contains a **thiol group (-SH)** with a pKa of approximately 8.3 - While closer to physiological pH than glycine or valine, its pKa is still ~1 pH unit away from 7.4 - Its buffering capacity at **pH 7.4** is significantly less effective than histidine's imidazole group

Q: What is the daily requirement of potassium in a healthy adult?

4-5 g/day. ***4-5 g/day*** - The recommended daily intake of **potassium** for a healthy adult is approximately **3,500-4,700 mg (3.5-4.7g)**, making **4-5 g/day** the most accurate answer. - This range aligns with the **Adequate Intake (AI)** recommendations from major health organizations. - Adequate potassium is crucial for maintaining proper **fluid balance**, **nerve impulses**, **muscle contraction**, and **blood pressure regulation**. *3-4 g/day* - While this range covers the minimum requirement (3.5g), it falls short of the **optimal intake of 4.7g**. - This amount may be adequate but is lower than the recommended target for cardiovascular health benefits. *2-3 g/day* - This amount is **below the minimum recommended intake** of potassium for healthy adults. - Consistent intake at this level can lead to **hypokalemia**, potentially affecting **blood pressure regulation**, **muscle function**, and increasing risk of **cardiovascular disease**. *5-7 g/day* - This intake is higher than the typical recommended daily allowance for most healthy adults. - While high potassium intake is generally safe for individuals with **healthy kidneys**, very high levels can be a concern for those with **renal impairment** or taking certain medications.

Q: Concentration of H+ ion is 10-9. What is the pH of the solution?

9. ***9*** - This option is correct based on the **fundamental definition of pH**. pH is the negative logarithm (base 10) of the **hydrogen ion concentration ([H+])**. Therefore, if [H+] is 10^-9 M, the pH = -log(10^-9) = **9**. - A pH of **9 indicates a slightly alkaline (basic) solution**, as it is above the neutral pH of 7. *7* - This would be the pH if the **hydrogen ion concentration [H+] were 10^-7 M**, which represents a **neutral solution**. - This is incorrect for the given concentration of 10^-9 M and indicates a calculation error. *13* - This pH value represents a **highly alkaline (basic) solution**, corresponding to a very low [H+] of 10^-13 M. - This is significantly different from the given [H+] of 10^-9 M and indicates a misunderstanding of the logarithmic pH scale. *4* - This pH value represents an **acidic solution**, corresponding to a higher [H+] of 10^-4 M. - This is an incorrect calculation and does not match the given hydrogen ion concentration of 10^-9 M.

Q: Osmolarity of 4.2% solution of sodium bicarbonate is ?

1000 osmole/litre. ***1000 osmole/litre*** - To calculate osmolarity, convert the percentage to grams per liter (4.2% = 42 g/L). Divide by the **molecular weight of NaHCO₃ (84 g/mol)** to get moles/L (42/84 = 0.5 mol/L). - Since NaHCO₃ dissociates into two particles (Na⁺ and HCO₃⁻), multiply the molarity by 2 to get osmolarity (0.5 mol/L * 2 = **1 osmol/L or 1000 mOsmol/L**). *1500 osmole/litre* - This value would be correct if the molar concentration was 0.75 mol/L (0.75 x 2 = 1.5 osmol/L), which is not the case for a 4.2% solution. - This calculation might arise if an incorrect molecular weight or dissociation factor was used. *2000 osmole/litre* - This would require a molar concentration of 1 mol/L (1 x 2 = 2 osmol/L), meaning 84 grams of NaHCO₃ per liter, which is far greater than the 42 g/L provided. - This suggests an overestimation of the concentration or an incorrect calculation of dissociation. *500 osmole/litre* - This value suggests that either the dissociation factor of 2 was not applied, or the initial molar concentration was mistakenly calculated as 0.25 mol/L. - It would imply that the solution is half as concentrated as it truly is in terms of osmotic particles.

Q: What is the normal serum magnesium level?

1.5-2.5 mEq/L. ***1.5-2.5 mEq/L*** - The **normal serum magnesium range** in adults is **1.5 to 2.5 mEq/L** (or 1.7-2.2 mg/dL, or 0.7-1.0 mmol/L). - Magnesium plays a crucial role in various bodily functions, including **muscle and nerve function**, **blood glucose control**, **blood pressure regulation**, and as a cofactor in over **300 enzymatic reactions**. - Approximately **99% of total body magnesium is intracellular**, making serum levels only a partial reflection of total body stores. *50 mEq/L* - A serum magnesium level of **50 mEq/L** is extremely high and would indicate **severe hypermagnesemia**, which is a life-threatening condition. - This level is far outside the normal physiological range and would lead to immediate and serious **cardiac arrest** and **neurological complications**. *5 mEq/L* - A serum magnesium level of **5 mEq/L** is significantly elevated and suggests **hypermagnesemia**. - While not as immediately lethal as 50 mEq/L, this level is still a medical emergency and can cause symptoms like **hypotension**, **bradycardia**, **muscle weakness**, and **decreased deep tendon reflexes**. *25 mEq/L* - A serum magnesium level of **25 mEq/L** represents profound **hypermagnesemia** and is incompatible with life. - This level would lead to immediate **cardiac arrest** and **respiratory paralysis**.

Question 1

Which of the following phospholipids serves as a marker of apoptosis?

Accepted Answer

Phosphatidylserine

Answer

Phosphatidylinositol

Answer

Phosphatidylcholine

Answer

Phosphatidylethanolamine

Question 2

In metabolic alkalosis, which statement is true about urinary excretion?

Accepted Answer

Decreased excretion of ammonia

Answer

Increased excretion of NH3

Answer

Decreased excretion of aceto-acetic acid

Answer

Excretion of betahydroxy butyric acid

Question 3

Which of the following amino acids primarily acts as a buffer in blood due to its ability to accept and donate protons at physiological pH?

Accepted Answer

Histidine

Answer

Arginine

Answer

Tryptophan

Answer

Tyrosine

Question 4

The following reaction occurs in which part of kidney?

Accepted Answer

Proximal convoluted tubule

Answer

Distal convoluted tubule

Answer

Loop of Henle

Answer

Collecting duct

Question 5

Which one of the following biochemical abnormalities can be produced by repeated vomiting?

Accepted Answer

Metabolic alkalosis

Answer

Metabolic acidosis

Answer

Ketosis

Answer

Uraemia

Question 6

Maximum buffering capacity at physiological pH is for:

Accepted Answer

Histidine

Answer

Glycine

Answer

Valine

Answer

Cysteine

Question 7

What is the daily requirement of potassium in a healthy adult?

Accepted Answer

4-5 g/day

Answer

3-4 g/day

Answer

2-3 g/day

Answer

5-7 g/day

Question 8

Concentration of H+ ion is 10-9. What is the pH of the solution?

Accepted Answer

9

Answer

7

Answer

13

Answer

4

Question 9

Osmolarity of 4.2% solution of sodium bicarbonate is ?

Accepted Answer

1000 osmole/litre

Answer

1500 osmole/litre

Answer

2000 osmole/litre

Answer

500 osmole/litre

Question 10

What is the normal serum magnesium level?

Accepted Answer

1.5-2.5 mEq/L

Answer

50 mEq/L

Answer

5 mEq/L

Answer

25 mEq/L

Acid-Base and Electrolyte Balance — MCQs

Acid-Base and Electrolyte Balance — MCQs

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