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

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

APUD-system cells are hormone-active neuroendocrine cells possessing a universal property to absorb amine precursors, decarboxylate them and synthesize amines necessary for the construction and operation of regular peptides (amine precursor uptake and decarboxydation [APUD] cells).

Apodocytes 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 a gastroenteropancreatic endocrine system, which is, therefore, part of the APUD system.

The gastroenteropancreatic endocrine system consists of the following major endocrine cells secreting certain hormones.

The most important apodocytes of the gastroenteropancreatic endocrine system and the hormones secreted by them

A-cells	Glucagon
B cells	Insulin
D-cells	Somatostatin
0-1-cells	The vasoactive intestinal polypeptide (VIP)
Yeoc 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-pancreosimin
K-cells	Gastroinhibitory peptide
L-cells	Glitsentin, glucagon, polypeptide YY
Mo-cells	Motilin
N-cells	Neurotensin
R-eyelashes	Bombesin
PP cells	Pancreatic polypeptide
S-cells	Secretin
YY cells	YY polypeptide
VL-cells	ACTH (adrenocorticotropic hormone)

From the APUD-system cells, tumors-apodomas develop, while they can retain the ability to secrete the polypeptide hormones peculiar to the cells from which they originated.

Tumors that develop from the appendicitis of the gastrointestinal tract and pancreas are now commonly called gastroenteropancreatic endocrine tumors. At present, about 19 types of such tumors and more than 40 products of their secretion are described. Most tumors have the ability to secrete several hormones at the same time, but the clinical picture is determined by the predominance of the secretion of a single hormone. The main gastroenteropancreatic endocrine tumors having the greatest clinical significance are insulinoma, somatostatinoma, glucagonoma, gastrinoma, VIPoma, carcinoid. These tumors are usually malignant, with the exception of insulin.

[1], [2], [3], [4]