APUD

APUD

The term APUD refers to a group of cells that share certain characteristics, specifically the ability to take up amine precursors and decarboxylate them. This concept was first introduced by the British scientist A.G.E. Pearse in the 1960s. APUD cells are part of the diffuse neuroendocrine system and are found throughout the body, particularly in the gastrointestinal tract, pancreas, and respiratory system.

Characteristics

APUD cells are characterized by their ability to:

1. Amine Precursor Uptake: These cells can take up amine precursors from the bloodstream. 2. Decarboxylation: They possess enzymes that allow them to decarboxylate these precursors, converting them into active amines. 3. Hormone Secretion: APUD cells often secrete peptide hormones or biogenic amines, which play roles in various physiological processes.

Locations and Functions

APUD cells are distributed throughout the body and are involved in numerous functions:

• Gastrointestinal Tract: In the gut, APUD cells include enterochromaffin cells, which secrete serotonin, and G cells, which secrete gastrin.
• Pancreas: In the pancreas, APUD cells include insulin-secreting beta cells and glucagon-secreting alpha cells.
• Respiratory System: In the lungs, APUD cells can be found in the bronchial epithelium, where they may play a role in regulating airway tone.

Clinical Significance

APUD cells are implicated in various diseases, particularly neuroendocrine tumors. These tumors can arise from any APUD cell and are often classified based on their site of origin and the hormones they secrete.

• Carcinoid Tumors: These are slow-growing tumors that often originate in the gastrointestinal tract and can secrete serotonin, leading to carcinoid syndrome.
• Insulinomas: Tumors of the pancreatic beta cells that secrete insulin, causing hypoglycemia.
• Gastrinomas: Tumors that secrete gastrin, leading to Zollinger-Ellison syndrome.

History

The APUD concept was developed by A.G.E. Pearse, who proposed that these cells shared a common embryological origin from the neural crest. This idea has since evolved, and while the neural crest origin is not universally accepted, the functional similarities of APUD cells remain a useful classification.

Also see

• Neuroendocrine tumor
• Enterochromaffin cell
• Carcinoid syndrome
• Zollinger-Ellison syndrome