Hormonal Regulation

6 min read Updated Mar 26, 2026

Three hormones dominate renal regulation: ADH, aldosterone, and ANP. Each responds to a different stimulus, acts on a different part of the nephron, and produces a different effect. But they all serve the same ultimate goal - maintaining blood volume, blood pressure, and electrolyte balance.

The MCAT tests these hormones constantly. If you know the trigger, target, and effect of each hormone, you can reason through almost any renal physiology question.

Kidney cross-section showing cortex, medulla, renal pelvis, with inset nephron detail showing glomerulus, tubules, and loop of Henle — Kidney cross-section with nephron placement. Glomeruli and convoluted tubules sit in the cortex, while the loops of Henle dip into the medulla. Hormones (ADH, aldosterone, ANP) act on specific nephron segments to regulate water and ion balance. *Credit: Wikimedia Commons, CC BY-SA 3.0*

ADH (Antidiuretic Hormone / Vasopressin)

Trigger: Increased blood osmolarity (detected by hypothalamic osmoreceptors) or decreased blood volume/pressure (detected by baroreceptors in the carotid sinus and aortic arch)

Source: Synthesized in the hypothalamus, released from the posterior pituitary

Target: Receptors on collecting duct principal cells

Effect: Inserts aquaporin-2 channels into the apical membrane, increasing water reabsorption. Also promotes urea recycling in the inner medullary collecting duct.

Net result: Decreased urine volume, increased urine concentration, decreased blood osmolarity

Inhibited by: Low blood osmolarity, alcohol, ANP

Aldosterone

Trigger: Angiotensin II (from RAAS), high blood K+, low blood Na+, and ACTH (minor role)

Source: Zona glomerulosa of the adrenal cortex

Target: Principal cells of the DCT and collecting duct

Effect: Increases expression of sodium channels on the apical membrane and Na+/K+ ATPase on the basolateral membrane. This increases Na+ reabsorption and K+ secretion.

Net result: Na+ and water retention (water follows sodium), K+ excretion, increased blood volume and blood pressure

Inhibited by: ANP, high blood Na+, low K+

ANP (Atrial Natriuretic Peptide)

Trigger: Atrial stretch from increased blood volume (the atria of the heart release ANP when they are overfilled)

Source: Cardiac atrial myocytes

Target: Multiple sites - kidneys, adrenal glands, blood vessels, hypothalamus

Effects:

Increases GFR (dilates afferent arteriole, constricts efferent arteriole)
Inhibits Na+ reabsorption in the collecting duct
Inhibits renin release (suppresses RAAS)
Inhibits aldosterone secretion
Inhibits ADH release
Causes vasodilation

Net result: Increased Na+ and water excretion, decreased blood volume and blood pressure

Head-to-Head Comparison

Feature	ADH	Aldosterone	ANP
Stimulus	High osmolarity, low BP	Angiotensin II, high K+	Atrial stretch (high volume)
Source	Posterior pituitary	Adrenal cortex (zona glomerulosa)	Heart atria
Primary target	Collecting duct (principal cells)	DCT and collecting duct (principal cells)	Kidneys, adrenals, vessels
Mechanism	Inserts aquaporin channels	Upregulates Na+ channels and Na+/K+ ATPase	Dilates afferent arteriole, blocks Na+ reabsorption
Effect on Na+	Minimal direct effect	Increases reabsorption	Increases excretion
Effect on K+	No direct effect	Increases secretion	No major direct effect
Effect on water	Increases reabsorption	Increases reabsorption (follows Na+)	Increases excretion
Effect on BP	Increases	Increases	Decreases
Urine volume	Decreases	Decreases	Increases

How the Three Hormones Interact

Dehydration scenario:

Blood osmolarity rises and blood volume drops
ADH is released - collecting duct reabsorbs water
RAAS is activated - aldosterone causes Na+ (and water) retention
ANP is suppressed (atria are not stretched)
Result: concentrated, low-volume urine; blood volume and pressure restored

Overhydration scenario:

Blood volume rises, blood osmolarity drops
ADH is suppressed - collecting duct stays impermeable
RAAS is suppressed - less aldosterone, less Na+ retention
ANP is released - promotes Na+ and water excretion, further suppresses RAAS and ADH
Result: dilute, high-volume urine; blood volume and pressure decrease

A patient takes a drug that blocks aldosterone receptors. Predict the effects on Na+, K+, blood pressure, and urine volume.

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Blocking aldosterone prevents Na+ reabsorption and K+ secretion in the DCT and collecting duct. Blood Na+ decreases (and water follows, so blood volume and blood pressure drop). Blood K+ increases (hyperkalemia - the main risk of this drug class). Urine volume increases (Na+ and water are lost). This type of drug is classified as a "potassium-sparing diuretic."

A patient has congestive heart failure with high blood volume. Which hormone is elevated, and why does the kidney still retain sodium?

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ANP is elevated (atria are stretched by high blood volume), but the kidney still retains sodium because RAAS is also activated. In CHF, cardiac output is low, so renal perfusion is reduced. The kidneys interpret low perfusion as low blood volume and activate RAAS, causing sodium and water retention despite total body fluid overload. The RAAS signal overrides ANP in this context. This is the pathological "vicious cycle" of CHF.