APUD (APUD) tumors - systems: causes, symptoms, diagnosis, treatment

The APUD system is a diffuse endocrine system that unites cells present in virtually all organs and synthesizes biogenic amines and numerous peptide hormones. It is an actively functioning system that maintains homeostasis in the body.

The cells of the APUD system (apudocytes) are hormonally active neuroendocrine cells that have the universal property of absorbing amine precursors, decarboxylating them, and synthesizing amines necessary for the construction and functioning of regular peptides (amine precursor uptake and decarboxydation [APUD] cells).

Apudocytes have a characteristic structure, histochemical, immunological features that distinguish them from other cells. They contain endocrine granules in the cytoplasm and synthesize the corresponding hormones.

Many types of apudocytes are found in the gastrointestinal tract and pancreas and form the gastroenteropancreatic endocrine system, which is thus part of the APUD system.

The gastroenteropancreatic endocrine system consists of the following major endocrine cells that secrete specific hormones.

The most important apudocytes of the gastroenteropancreatic endocrine system and the hormones they secrete

A-cells	Glucagon
B cells	Insulin
D-cells	Somatostatin
0-1 cells	Vasoactive intestinal polypeptide (VIP)
Yos-cells	Serotonin, substance P, melatonin
Eel cells	Histamine
G cells	Gastrin
JC cells	Large gastrin
TG cells	Small gastrin
GER cells	Endorphins, enkephalins
J-cells	Cholecystokinin-pancreozymin
K-cells	Gastroinhibitory peptide
L-cells	Glycentin, glucagon, polypeptide YY
Mo cells	Motilin
N-cells	Neurotensin
R-petki	Bombesin
PP cells	Pancreatic polypeptide
S-cells	Secretin
YY cells	YY polypeptide
VL cells	ACTH (adrenocorticotropic hormone)

Apudoma tumors develop from cells of the APUD system, and they can retain the ability to secrete polypeptide hormones characteristic of the cells from which they arose.

Tumors developing from apudocytes of the gastrointestinal tract and pancreas are now commonly called gastroenteropancreatic endocrine tumors. Currently, about 19 types of such tumors and more than 40 products of their secretion have been described. Most tumors have the ability to secrete several hormones simultaneously, but the clinical picture is determined by the predominance of secretion of any one hormone. The main gastroenteropancreatic endocrine tumors of greatest clinical significance are insulinoma, somatostatinoma, glucagonoma, gastrinoma, VIPoma, and carcinoid. These tumors are usually malignant, with the exception of insulinomas.

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