Step by Step
Alpha
Alpha cells — glucagon
Alpha cells make up about 20% of the islets of Langerhans and release glucagon when blood glucose falls (as during fasting). Glucagon raises blood glucose by increasing glycogenolysis and gluconeogenesis in the liver — a catabolic hormone.
Beta
Beta cells — insulin
Beta cells make up about 70% of the islets and release insulin when blood glucose rises (as after eating). Insulin lowers blood glucose by increasing glucose uptake in muscle and fat (via GLUT4 insertion), increasing glycogen synthesis, increasing protein synthesis, increasing fat storage, and decreasing gluconeogenesis — overall, an anabolic hormone.
Delta
Delta cells — somatostatin
Delta cells make up about 10% of the islets and release somatostatin, which inhibits both insulin and glucagon release, as well as inhibiting growth hormone and GI secretions.
DM
Diabetes mellitus — two distinct mechanisms
Type 1 diabetes results from autoimmune destruction of beta cells, leading to no insulin production at all. Type 2 diabetes involves insulin resistance combined with a relative (not absolute) insulin deficiency.
Applied Walkthrough
1
After a carbohydrate-rich meal, blood glucose rises, triggering beta cells to release insulin — promoting glucose uptake into muscle and fat cells, glycogen synthesis, and reduced gluconeogenesis, all working together to bring blood glucose back down.
2
During an overnight fast, blood glucose gradually falls, triggering alpha cells to release glucagon instead — promoting glycogen breakdown and new glucose production in the liver, raising blood glucose back toward normal.
3
A patient newly diagnosed with Type 1 diabetes has had their beta cells destroyed by an autoimmune process — they can no longer produce insulin at all, regardless of how high their blood glucose rises.
4
A different patient with Type 2 diabetes still produces insulin, but their tissues respond poorly to it (insulin resistance), and their beta cells eventually can't keep up with the increased demand — a fundamentally different mechanism from Type 1, despite both resulting in elevated blood glucose.
Exam Application
Exams test whether you can match each islet cell type (alpha, beta, delta) to its hormone and function, whether you understand insulin and glucagon as opposing (anabolic vs. catabolic) hormones, and whether you can distinguish the mechanisms of Type 1 versus Type 2 diabetes.
⚠ Common Trap
The most common trap is confusing which cell type does what — remember alpha cells release glucagon (which makes glucose go up), while beta cells release insulin (which brings glucose down) — the memory anchor "alpha goes up, beta brings down" helps keep this straight.
✓ Quick Self-Check
1. What hormone do alpha cells release, and what does it do to blood glucose?
Glucagon, which raises blood glucose.
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2. What hormone do beta cells release, and what does it do to blood glucose?
Insulin, which lowers blood glucose.
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3. What does somatostatin do, and which cells release it?
Inhibits both insulin and glucagon release (also GH and GI secretions); released by delta cells.
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4. What is the underlying mechanism of Type 1 diabetes?
Autoimmune destruction of beta cells, resulting in no insulin production.
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5. What is the underlying mechanism of Type 2 diabetes?
Insulin resistance combined with a relative insulin deficiency.
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