# ADH: How the Kidney Conserves Water

Andrew Bland, MD, FACP, FAAP · October 19, 2026

ADH changes the collecting duct’s permeability to water. Its principal renal effect is water conservation, so connect the hormone to tonicity and urine concentration.

![Diagram](https://urinenephrology.org/2025_UDPA_Lectures_Live/assets/adh-kidney-effects-2026-10-19.png)

## What triggers ADH?

Rising plasma tonicity is a major stimulus. Low effective circulating volume can also drive ADH release, even when serum sodium is already low.

## Where does it come from?

ADH, also called vasopressin, is synthesized in the hypothalamus and released from the posterior pituitary.

## Follow the collecting-duct mechanism

ADH binds basolateral V2 receptors on principal cells. The cAMP/PKA pathway increases insertion of aquaporin-2 in the apical membrane; water exits through basolateral aquaporin-3 and aquaporin-4.

## The gradient makes water movement possible

Water moves down an osmotic gradient toward the medullary interstitium and blood. ADH supplies permeability; a functioning medullary concentration gradient is also needed.

## Connect urine and blood

More ADH generally means less water excretion and more concentrated urine. Reduced ADH allows more dilute urine when the kidney can dilute normally. ADH is not simply a sodium-retaining hormone: interpret serum sodium as a water-balance clue and assess volume separately.

## Supporting evidence

- [Primary study: vasopressin and aquaporin redistribution](https://pubmed.ncbi.nlm.nih.gov/7532304/)
- [NIDDK: Your Kidneys & How They Work](https://www.niddk.nih.gov/health-information/kidney-disease/kidneys-how-they-work)

## Continue learning

- [Opening lecture: ADH](https://urinenephrology.org/2025_UDPA_Lectures_Live/case-based-lectures/opening-lecture.html#adh-diagram)
- [Electrolyte lectures](https://urinenephrology.org/2025_UDPA_Lectures_Live/electrolytes/index.html)
- [Edema lecture](https://urinenephrology.org/2025_UDPA_Lectures_Live/edema/index.html)
- [RAAS and kidney effects](https://urinenephrology.org/visual-reference/raas-kidney-effects.html)
- [Case lecture series](https://urinenephrology.org/2025_UDPA_Lectures_Live/case-based-lectures/index.html)