14.1.10—Negative feedback control of blood glucose

Blood glucose is regulated by opposing negative-feedback responses. A rise is detected by pancreatic beta cells, which release insulin to promote glucose uptake and storage; a fall is detected by alpha cells, which release glucagon to promote glucose release and production.

High blood glucose control:

1. Beta cells in the pancreatic islets release insulin.
2. Insulin stimulates glucose uptake by liver, muscle and adipose target cells; it also supports glucose use in respiration.
3. Insulin promotes glycogenesis, so glucose is stored as glycogen and the blood concentration falls towards its functional range.

Low blood glucose control:

1. Alpha cells release glucagon while insulin secretion decreases.
2. Glucagon acts mainly on liver cells to stimulate glycogenolysis and, when needed, glucose production from non-carbohydrate substrates.
3. The liver releases more glucose into the blood, opposing the fall.

Insulin and glucagon act in opposite directions but are not identical mirror images in every tissue: liver, muscle and adipose cells have different roles. Muscle glycogen supports that muscle rather than being the main source of blood glucose. This card covers hormonal negative feedback, not test strips or biosensor readouts.