Question

The major electrolyte lost through gastrointestinal fluid during vomition is mainly

• A. Sodium and chloride
• B. Sodium and Potassium
• C. Potassium and chloride
• D. Potassium and bicarbonate

Hint:

Remember the diagnostic biochemistries:
- Vomiting (loss of stomach acid) $\rightarrow$ Loss of Sodium and Chloride $\rightarrow$ Hypochloremic Metabolic Alkalosis.
- Diarrhea (loss of alkaline pancreatic secretions) $\rightarrow$ Loss of Sodium and Bicarbonate $\rightarrow$ Hyperchloremic Metabolic Acidosis.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Vomiting (emesis) results in the forceful expulsion of gastric contents.
Gastric secretions are rich in hydrochloric acid ($\text{HCl}$), sodium ($\text{Na}^+$), and potassium ($\text{K}^+$), and their loss leads to systemic electrolyte and acid-base imbalances.

Step 2: Detailed Explanation:
Gastric juice contains high concentrations of hydrogen ions ($\text{H}^+$) and chloride ions ($\text{Cl}^-$) secreted by the parietal cells, along with sodium ($\text{Na}^+$) and potassium ($\text{K}^+$) ions.
Although vomiting is classically associated with hypokalemia (due to potassium loss and subsequent renal compensation) and metabolic alkalosis (due to loss of gastric acid), in terms of absolute mass, the most abundant electrolytes lost in the gastric fluid are sodium and chloride.
Sodium ($\text{Na}^+$) is the principal extracellular cation, and chloride ($\text{Cl}^-$) is the major extracellular anion in these secretions.
Severe vomiting therefore leads to rapid depletion of circulating volume, hyponatremia, and profound hypochloremia.
Bicarbonate ($\text{HCO}_3^-$) is typically conserved or elevated in the blood during vomiting due to metabolic alkalosis, so it is not lost in large amounts (unlike in diarrhea, where bicarbonate loss is significant).

Step 3: Final Answer:
Therefore, the major electrolytes lost during vomiting are sodium and chloride, making option (A) the correct choice.