[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Biochemistry](https://durgical.com/en/biochemistry/) › Ammonia (ammonium)

[Biochemistry](https://durgical.com/en/biochemistry/) · Molecule

# Ammonia (ammonium)

Ammonia comes from breaking down amino acids. It is toxic to the brain, so the liver turns it into urea.

Updated 2026-11-01

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## Key facts

- At body pH almost all of it is ammonium ion (NH₄⁺); the small NH₃ fraction crosses membranes, including the blood–brain barrier.
- Sources: deamination of glutamate (glutamate dehydrogenase), glutaminase in kidney and gut, and colonic bacteria.
- It travels in blood as glutamine (from almost every tissue) and as alanine (from muscle).
- The liver removes it as urea; the kidney excretes NH₄⁺ to get rid of acid.

**Also called**
NH₃ / NH₄⁺

**Formula**
NH₃

**PubChem**
[CID 222](https://pubchem.ncbi.nlm.nih.gov/compound/222)

## Structure

- A small pyramidal molecule: one nitrogen with three hydrogens and a lone pair that accepts a proton (pKa near 9.2).

## Clinical notes

- In hyperammonaemia, astrocytes turn ammonia into glutamine, swell, and cerebral oedema follows.
- Causes: urea cycle disorders and organic acidaemias in children; cirrhosis and GI bleeding in adults.
- Lactulose acidifies the colon and traps NH₄⁺; rifaximin reduces the bacteria that make it.
- An ammonia sample is processed fast and on ice, because the level rises in the tube.

## Drugs that act here

- [Lactulose](https://durgical.com/en/pharmacology/lactulose/)

## Pathways

- [Urea cycle](https://durgical.com/en/biochemistry/pathways/urea-cycle/)

## Related conditions

- [Hyperammonaemia](https://durgical.com/en/conditions/hyperammonaemia/)
- [Ornithine transcarbamylase (OTC) deficiency](https://durgical.com/en/conditions/ornithine-transcarbamylase-deficiency/)
- [Cirrhosis](https://durgical.com/en/conditions/cirrhosis/)

## Related

- [Urea](https://durgical.com/en/biochemistry/molecules/urea/)
- [Glutamine](https://durgical.com/en/biochemistry/molecules/glutamine/)
- [Glutamate (glutamic acid)](https://durgical.com/en/biochemistry/molecules/glutamate/)
- [Glutamate dehydrogenase (GDH)](https://durgical.com/en/biochemistry/enzymes/glutamate-dehydrogenase/)
- [Glutamine synthetase](https://durgical.com/en/biochemistry/enzymes/glutamine-synthetase/)
- [Carbamoyl phosphate synthetase I (CPS-I)](https://durgical.com/en/biochemistry/enzymes/carbamoyl-phosphate-synthetase-i/)

## Test yourself

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

## Which form of ammonia crosses the blood–brain barrier?

Uncharged NH₃; although it is a small fraction at body pH, it passes membranes easily.

## How does ammonia travel from tissues to the liver without poisoning them?

As glutamine (glutamine synthetase) and, from muscle, as alanine (glucose–alanine cycle).

## Why is an ammonia sample carried on ice?

Because cells and time in the tube release ammonia and give falsely high values.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/biochemistry/molecules/ammonia/)

Molecules are shown in their neutral form, as the databases deposit them; in the cell the acids and phosphates are ionised.

Educational information, not medical advice. For any symptom, see a health professional.

Sources: [Ammonia (CID 222)](https://pubchem.ncbi.nlm.nih.gov/compound/222) (PubChem, NCBI, 2026) · Public domain; [Ammonia Levels: MedlinePlus Medical Test](https://medlineplus.gov/lab-tests/ammonia-levels/) (MedlinePlus, US National Library of Medicine, 2026); [Urea cycle](https://reactome.org/PathwayBrowser/#/R-HSA-70635) (Reactome, 2026).

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Representative model, for educational purposes only.

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