The main cation in extracellular fluid is:

Appeared in: UP NHM CHO 7 Sept 2022 (Shift-2)

Explanation

Sodium (Na⁺) is a cation, meaning it carries a positive electrical charge.
It is the most abundant electrolyte found in the extracellular fluid (ECF), the fluid environment outside of the body's cells.
Sodium plays a critical role in maintaining fluid balance, blood pressure, and the function of nerves and muscles.
The normal serum concentration of sodium is approximately 135–145 mEq/L, highlighting its high concentration in the ECF.

Option A: Sulfate (SO₄²⁻) is an anion, meaning it has a negative charge. The question asks for the main cation (positive charge).
Option B: Bicarbonate (HCO₃⁻) is a major anion (negative charge) in the ECF. It is crucial for the body's acid-base buffering system, but it is not a cation.
Option D: Chloride (Cl⁻) is the most abundant anion (negative charge) in the ECF. It often pairs with sodium to maintain electrical neutrality and osmotic pressure, but it is not a cation.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Fluid and Electrolyte Balance: Major Cations in Body Fluid Compartments as background academic context rather than a clinical decision trigger.
Monitoring a patient's sodium level is a fundamental nursing responsibility. Imbalances can lead to serious conditions.
Hyponatremia (low sodium) can cause confusion, seizures, and coma. Hypernatremia (high sodium) can lead to dehydration, thirst, and neurological changes.
Nurses must carefully manage intravenous fluids and monitor intake and output to prevent iatrogenic (illness caused by medical examination or treatment) sodium imbalances.

How to Approach the Question

First, break down the question. Identify the two key terms: 'main cation' and 'extracellular fluid' (ECF).
Recall the definition of a cation: a positively charged ion. This allows you to evaluate the options based on their electrical charge.
Differentiate between cations and anions. Sulfate, bicarbonate, and chloride are all anions (negatively charged), which immediately eliminates them as potential answers.
Recall the distribution of major electrolytes in the body's fluid compartments. Sodium (Na⁺) is the primary cation in the ECF, while potassium (K⁺) is the primary cation in the intracellular fluid (ICF).
Based on this knowledge, conclude that Sodium is the main cation in the extracellular fluid.

Concept Tested & Keywords

Concept Tested: Fluid and Electrolyte Balance: Major Cations in Body Fluid Compartments
Stem keywords: cation, extracellular fluid, ECF
Lead-in keywords: main
Negative lead-in flag: false

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E6 Nursing Fundamentals Taylor pp. 773-775, 772-774

E6 Pharmacology Nursing Lilley 11e Part 2 p. 164-166

Practise the full UP NHM CHO 7 Sept 2022 (Shift-2)

Attempt every question from this paper in a timed mock, then review the full solution for each one.