Corpus: Adrenal medulla

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Synonyms: Medulla glandulae suprarenalis, NNM
English: , adrenal marrow

1. Definition[Bearbeiten]

The adrenal medulla, or NNM for short, forms the smallest part of the adrenal gland. It is a sympathetic paraganglion consisting of chromaffin cells that synthesise the catecholamines adrenaline (80%) and noradrenaline (20%) from L-tyrosine.

2. Histology[Bearbeiten]

Two types of chromaffin cells can be distinguished in the adrenal medulla:

  • Type 1 ("A cell", "epinephrocytus") has large chromaffin granules, which have a diameter of 100-300 nm. They contain adrenalin. A cells make up about 80% of chromaffin cells.
  • Type 2 ("N-cell", "Norepinephrocytus") is filled with small, very dense granules containing noradrenaline. N-cells represent about 20% of chromaffin cells.

The chromaffin cells are arranged in the form of groups or cell strands around dilated capillaries or venules. In addition, the adrenal medulla contains connective tissue, multipolar sympathetic ganglion cells, undifferentiated sympathicoblasts and nerve fibres.

The strong blood supply to the adrenal glands guarantees the rapid transfer of hormones into the blood. The blood flows via sinusoids from the cortex into the medulla, exposing it to high concentrations of bovine hormones. In this way, cortisol can influence the release of catecholamines.


3. Innervation[Bearbeiten]

The multipolar ganglion cells of the adrenal medulla are innervated by preganglionic sympathetic nerve fibres from the greater splanchnic nerve and the lesser splanchnic nerve. They release the neurotransmitter acetylcholine, which binds to the nicotinic ACh receptors of the chromaffin cells.

4. Embryology[Bearbeiten]

The cells of the adrenal medulla originate from the ectodermal neural crest and migrate into the adrenal gland in the course of embryogenesis. There is therefore a developmental relationship to the sympathetic paraganglia.

5. Clinic[Bearbeiten]

Hyperfunction due to increased release of catecholamines is caused by a tumour of the NNM, the so-called pheochromocytoma.

6. Trivia[Bearbeiten]

The adrenal medulla is one of the organs with the highest concentration of vitamin C in the human body. It is used there to synthesise catecholamines.

See also: Adrenal cortex

7. Podcast[Bearbeiten]

8. Image source[Bearbeiten]

  • Podcast image source: ©Kamran Chaudhry / Unsplash

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