The hormone that increases water reabsorption by inserting water channel or aquaporins is:

ESIC Nursing Officer -2019 (Shift -1)

Applied Physiology

Easy

Appeared in: ESIC Nursing Officer -2019 (Shift -1)

Explanation

Anti-diuretic hormone (ADH), also called vasopressin, directly increases the permeability of the collecting ducts and distal tubules to water.
ADH achieves this by stimulating the insertion of aquaporin-2 (AQP2) water channels into the apical membranes of the renal tubular cells.
This mechanism allows for the passive reabsorption of water from the tubular fluid back into the bloodstream, concentrating the urine and conserving body water.
The release of ADH is primarily stimulated by an increase in plasma osmolarity (a sign of dehydration).

Option A: Angiotensin II's primary roles are vasoconstriction and stimulating the release of aldosterone and ADH. It does not directly insert water channels, making its effect on water reabsorption indirect.
Option C: Aldosterone's primary action is to increase sodium reabsorption. While water follows the reabsorbed sodium, aldosterone does not directly regulate water channels (aquaporins).
Option D: Atrial natriuretic peptide (ANP) has the opposite effect. It promotes the excretion of sodium and water (natriuresis and diuresis) to decrease blood volume and pressure.

Visual 1: Diagram: A detailed illustration of a principal cell in the kidney's collecting duct. The visual should show the V2 receptor, the signaling pathway initiated by ADH binding, and the subsequent translocation and insertion of aquaporin-2 (AQP2) channels into the apical membrane, allowing water to pass through.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Hormonal regulation of renal water reabsorption as background academic context rather than a clinical decision trigger.
Understanding ADH function is critical for recognizing and managing fluid balance disorders.
Diabetes Insipidus (DI): A condition caused by a deficiency of ADH or the kidneys' inability to respond to it. This leads to the excretion of large volumes of dilute urine (polyuria) and intense thirst (polydipsia), risking severe dehydration.
Syndrome of Inappropriate ADH Secretion (SIADH): Characterized by excessive ADH release, leading to increased water reabsorption, dilutional hyponatremia (low blood sodium), and concentrated urine. This can cause cerebral edema and neurological symptoms.

How to Approach the Question

First, identify the key phrase in the question: "increases water reabsorption by inserting water channel or aquaporins."
This points to a very specific physiological mechanism, not just a general effect on water balance.
Review the functions of the hormones listed in the options.
Recall that while multiple hormones influence fluid balance, only one directly acts by controlling the placement of aquaporin water channels.
Eliminate options that work indirectly. Aldosterone's primary target is sodium, and Angiotensin II stimulates other hormones. ANP does the opposite.
Select the hormone whose primary mechanism matches the one described in the question, which is Anti-diuretic hormone (ADH).

Concept Tested & Keywords

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