Corpus: Paraganglion

Paraganglia are collections of epithelial-like, endocrine-active parenchymal cells. They are functionally located between the autonomic nervous system and the endocrine system.

In addition to the parenchyma cells, paraganglia have a well-vascularised interstitium and are surrounded on the outside by a connective tissue capsule. The main cells serve as chemosensors and are surrounded by a network of glial sheath cells.

Like the adrenal medulla, the paraganglia derive developmentally from sympathicoblasts. These are of ectodermal origin and migrate from the neural crest.

A distinction is made between two different forms of paraganglia:

• chromaffin, sympathetic paraganglia
• non-chromaffinic, parasympathetic paraganglia

Sympathetic paraganglia[Bearbeiten]

Sympathetic paraganglia contain chromaffin parenchymal cells that produce catecholamines. They include the retroperitoneal paraganglia such as the Zuckerkandl organ at the exit of the inferior mesenteric artery. The adrenal medulla is also considered a paraganglion due to its origin. It is therefore the largest paraganglion in the human body.

Parasympathetic paraganglia[Bearbeiten]

Parasympathetic paraganglia contain non-chromaffin parenchymal cells. They include:

• Glomus caroticum in the carotid bifurcation
• Glomus aorticum at the aortic arch

These two paraganglia send afferents to the CNS with the vagus nerve (nerve X) and the glossopharyngeal nerve (nerve IX). They serve as chemoreceptors. There are also other parasympathetic paraganglia:

• Glomus jugulare (paraganglion jugulare)
• Glomus laryngicum superius (paraganglion laryngicum superius)
• Glomus laryngicum inferius (Paraganglion laryngicum inferius)
• Glomus tympanicum (paraganglion tympanicum)

All paraganglia serve as chemosensors. They recognise and react to a falling oxygen partial pressure or a rising carbon dioxide partial pressure in the arteries.

The sympathetic paraganglia are weakly innervated. This is why they release noradrenaline into the blood largely autonomously when stimulated. As a result, the heart rate and blood pressure increase, which improves the oxygen supply to the organs.

The function of the parasympathetic paraganglia differs significantly from this. They have contact with synapses of afferent fibres of the vagus and glossopharyngeal nerves and release ATP as a neurotransmitter after stimulation. The ATP reaches the purinergic receptors of the afferent axons via pannexin half-channels. The nerve fibres depolarise and thereby increase the respiratory drive in the CNS.

There is also a paracrine function in parasympathetic paraganglia. The sensitivity of the chemosensors is probably influenced by the secretion of dopamine and other substances.

Neuroendocrine tumours, so-called paragangliomas, can originate from the paraganglia.