Beta for insulin, alpha for glucagon, delta for somatostatin
Expansion
| Cell | Proportion | Hormone | Action |
|---|---|---|---|
| Beta | 65 to 80 per cent, central | Insulin, and C-peptide | Lowers glucose, anabolic |
| Alpha | 15 to 20 per cent, peripheral | Glucagon | Raises glucose |
| Delta | 3 to 10 per cent | Somatostatin | Inhibits both, and much else |
| PP (F) | 1 per cent | Pancreatic polypeptide | Inhibits pancreatic secretion |
| Epsilon | Under 1 per cent | Ghrelin | Appetite |
“Beta is biggest and central; alpha sits around the outside.”
The islets are about 1 to 2 per cent of pancreatic mass but receive a disproportionate share of the blood supply, and blood flows from beta cells outwards, so insulin reaches alpha cells at high concentration and suppresses glucagon locally.
C-peptide is the clinically useful consequence: it is cleaved from proinsulin in equimolar amounts with insulin, so it distinguishes endogenous insulin (C-peptide raised, as in insulinoma) from exogenous insulin (C-peptide suppressed, as in factitious hypoglycaemia).
Islet cell tumours: insulinoma (Whipple’s triad), gastrinoma (Zollinger-Ellison), glucagonoma (necrolytic migratory erythema, diabetes), VIPoma (watery diarrhoea, hypokalaemia, achlorhydria), somatostatinoma. Several occur in MEN 1.
Islet amyloid deposition of amylin is characteristic of type 2 diabetes.