IB Biology Topic D3.3.3: Regulation of Blood Glucose as an Example of the Role of Hormones in Homeostasis Notes

Insulin and Glucagon Keep Blood Glucose Within a Narrow Range

1. Blood glucose must be held steady as part of homeostasis.
2. Two hormones from the pancreas control it: insulin lowers blood glucose and glucagon raises it.
3. They act in opposition, so glucose stays within a narrow, healthy range.

The Pancreas Both Senses Glucose and Releases the Hormones

1. The pancreas acts as both the sensor and the responder for blood glucose.
2. The hormones come from clusters of cells called the islets of Langerhans.
   1. Beta cells secrete insulin, which lowers blood glucose.
   2. Alpha cells secrete glucagon, which raises blood glucose.

Negative Feedback Corrects Glucose in Both Directions

A change in blood glucose triggers a hormone that reverses that change, then switches off once glucose returns to normal.

1. High blood glucose after a meal.
   1. Beta cells detect the rise and secrete insulin.
   2. Insulin makes body cells take up glucose and makes the liver store it as glycogen by glycogenesis.
   3. Blood glucose falls back toward normal.
   4. Once glucose is normal, insulin secretion stops.
2. Low blood glucose between meals.
   1. Alpha cells detect the fall and secrete glucagon.
   2. Glucagon makes the liver break down glycogen into glucose by glycogenolysis.
   3. Blood glucose rises back toward normal.
   4. Once glucose is normal, glucagon secretion stops.
3. When this control system fails, the result is diabetes, covered in D3.3.4.