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[Physiology](https://durgical.com/en/physiology/) · [Endocrine](https://durgical.com/en/physiology/#s-endocrine)

# The posterior pituitary: ADH and oxytocin

- Regulation
- Exam priority: medium

The posterior pituitary releases two hypothalamic hormones: ADH, which makes the kidney save water, and oxytocin, for birth and milk.

Updated 2026-11-01

Also called: Vasopressin, Antidiuretic hormone, Oxytocin

**See it in 3D:** [Hypothalamus](https://durgical.com/en/anatomy/hypothalamus/) · [Pituitary gland](https://durgical.com/en/anatomy/pituitary-gland/)

## Key points

- Osmoreceptors (organum vasculosum of the lamina terminalis) sense ≈1–2% changes in osmolality; baroreceptors need ≈5–10% volume loss.
- ADH at the V2 receptor → cAMP → aquaporin 2 in the luminal membrane of the collecting duct; at V1 → vasoconstriction.
- Central diabetes insipidus (no ADH) versus nephrogenic (kidney does not respond): both give dilute urine and high sodium if water is not drunk.
- SIADH: ADH without a physiological stimulus → euvolemic hyponatremia with inappropriately concentrated urine.
- Oxytocin: milk ejection and uterine contraction; positive feedback in labor (Ferguson reflex).

## What it is

ADH and oxytocin are made in neurons of the supraoptic and paraventricular nuclei, travel down the axons bound to neurophysins and are released in the posterior pituitary. ADH responds mainly to plasma osmolality and, more strongly but less sensitively, to falling volume. Oxytocin responds to neuroendocrine reflexes: nipple suckling and stretch of the cervix.

## How it works, step by step

- Plasma osmolality rises: osmoreceptor neurons shrink and activate the ADH-producing neurons.
- Action potentials run down the stalk and release ADH into posterior pituitary capillaries; thirst is also triggered.
- In the collecting-duct principal cell, ADH activates V2 → cAMP → PKA, which inserts aquaporin 2 into the luminal membrane.
- Water moves into the hypertonic medullary interstitium and urine concentrates; ADH also adds urea transporters.
- Osmolality falls and ADH drops; within minutes the aquaporins are pulled back by endocytosis.

## Guide values

| Parameter | Value | Note |
| --- | --- | --- |
| Plasma osmolality | ≈275–295 mOsm/kg | |
| ADH release threshold | ≈280–285 mOsm/kg | |
| Possible urine osmolality | ≈50–1200 mOsm/kg | from maximal dilution to maximal concentration |
| Plasma sodium | ≈135–145 mEq/L | |

Approximate values for a healthy adult at rest; each laboratory sets its own ranges.

## Disorders of water and ADH

| Disorder | Plasma sodium | Urine | After water deprivation and ADH analog |
| --- | --- | --- | --- |
| [Central diabetes insipidus](https://durgical.com/en/conditions/hypernatraemia/) | High-normal or ↑ | Dilute, large volume | No concentration with deprivation; concentrates with the analog |
| [Nephrogenic diabetes insipidus](https://durgical.com/en/conditions/hypernatraemia/) | High-normal or ↑ | Dilute, large volume | Concentrates with neither |
| Primary polydipsia | Low-normal | Dilute, large volume | Concentrates with deprivation |
| [SIADH](https://durgical.com/en/conditions/syndrome-of-inappropriate-antidiuretic-hormone-secretion/) | ↓ | Concentrated, high urine sodium | Not applicable: the problem is too much ADH |

## Clinical notes

- SIADH: typical causes are small cell lung carcinoma, central nervous system disease, pneumonia and drugs.
- Lithium is a classic cause of nephrogenic diabetes insipidus; hypercalcemia and hypokalemia also blunt the response to ADH.
- Correcting chronic hyponatremia too fast can cause osmotic demyelination.

## Memory aid

ADH = "Add Dat H₂O": it opens the water gate in the collecting duct and adds water back to the blood.

## Test yourself

Think of the answer, then tap the question to see it.

## Why does SIADH cause hyponatremia without edema?

The retained water spreads through all compartments, and the mild volume expansion increases sodium excretion (natriuretic peptide, less aldosterone); extracellular volume stays near normal.

## How does the water deprivation test separate central from nephrogenic diabetes insipidus?

In both, urine stays dilute with deprivation. After an ADH analog, central DI concentrates the urine (the kidney responds) and nephrogenic DI does not.

## Why does a large hemorrhage release ADH even with normal osmolality?

Falling volume and pressure reduce baroreceptor firing; this stimulus is less sensitive than the osmotic one but far more powerful, and it puts volume ahead of osmolality.

## Why does nipple suckling cause milk ejection within seconds?

It is a neuroendocrine reflex: sensory nerves from the nipple activate paraventricular neurons that release oxytocin, which contracts the myoepithelial cells of the alveoli.

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## See it in 3D

The structures of Durgical's 3D anatomy where it happens.

- [Hypothalamus](https://durgical.com/en/anatomy/hypothalamus/)
- [Pituitary gland](https://durgical.com/en/anatomy/pituitary-gland/)

## Related topics

- [ADH, thirst and water balance](https://durgical.com/en/physiology/adh-thirst-and-water-balance/)
- [The countercurrent mechanism, urea recycling and urine concentration](https://durgical.com/en/physiology/the-countercurrent-mechanism-urea-recycling-and-urine-concentration/)
- [Urine dilution, free water and osmotic diuresis](https://durgical.com/en/physiology/urine-dilution-free-water-and-osmotic-diuresis/)
- [The hypothalamic–pituitary system: overview](https://durgical.com/en/physiology/the-hypothalamic-pituitary-system-overview/)
- [Lactation](https://durgical.com/en/physiology/lactation/)
- [The baroreceptor reflex](https://durgical.com/en/physiology/the-baroreceptor-reflex/)

## Related conditions

- [Syndrome of inappropriate antidiuretic hormone secretion (SIADH)](https://durgical.com/en/conditions/syndrome-of-inappropriate-antidiuretic-hormone-secretion/)
- [Hypernatraemia](https://durgical.com/en/conditions/hypernatraemia/)
- [Hyponatraemia](https://durgical.com/en/conditions/hyponatraemia/)

## In Biochemistry

- [G protein-coupled receptors and cAMP](https://durgical.com/en/biochemistry/topics/g-protein-coupled-receptors-and-camp/)

[← All of physiology](https://durgical.com/en/physiology/)

Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.

Sources: [17.3 The Pituitary Gland and Hypothalamus](https://openstax.org/books/anatomy-and-physiology-2e/pages/17-3-the-pituitary-gland-and-hypothalamus) (OpenStax (Rice University), 2022); [Syndrome of inappropriate antidiuretic hormone secretion: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000314.htm) (MedlinePlus, US National Library of Medicine, 2024); [Diabetes insipidus: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000377.htm) (MedlinePlus, US National Library of Medicine, 2024); [Antidiuretic hormone blood test: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/003702.htm) (MedlinePlus, US National Library of Medicine, 2024); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 76). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).

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Representative model, for educational purposes only.

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License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/physiology/the-posterior-pituitary-adh-and-oxytocin/