Pancreatic Cells: Understanding Alpha & Beta Cell Functions

The pancreatic islets of Langerhans contain five endocrine cell types. Alpha and beta cells are the primary regulators of glucose homeostasis.

Alpha Cells (α-cells, ~20% of islet mass)

• Product: Glucagon (29-aa peptide).
• Trigger: Low blood glucose (<70 mg/dL), amino acids (arginine), sympathetic activation.
• Actions:
  • Liver: Glycogenolysis, gluconeogenesis → ↑ blood glucose.
  • Adipose: Lipolysis → free fatty acids.
  • Heart: Positive inotropy (via cAMP).

Beta Cells (β-cells, ~65–80% of islet mass)

• Product: Insulin (51-aa, two chains), C-peptide, amylin (IAPP).
• Trigger: High blood glucose (>100 mg/dL), incretins (GLP-1, GIP), amino acids, parasympathetic.
• Actions:
  • Muscle/Adipose: GLUT4 translocation → glucose uptake.
  • Liver: Glycogen synthesis, inhibits gluconeogenesis/glycogenolysis.
  • Adipose: Lipogenesis, inhibits lipolysis.
  • Protein synthesis, K⁺ uptake.

Paracrine Crosstalk

• Insulin inhibits α-cells (via GABA, Zn²⁺).
• Glucagon stimulates β-cells (via GLP-1 receptor).
• Somatostatin (δ-cells) inhibits both.
• Pancreatic polypeptide (PP cells) regulates exocrine secretion.

Pathophysiology

• Type 1 DM: Autoimmune β-cell destruction → absolute insulin deficiency, unopposed glucagon.
• Type 2 DM: β-cell dysfunction + insulin resistance + relative glucagon excess.
• Glucagonoma (α-cell tumor): Diabetes, necrolytic migratory erythema, weight loss.