Blood Glucose Regulation by Glucagon

Overview

This lecture covers how the body regulates low blood glucose using the hormone glucagon, focusing on homeostasis and the processes involved.

Glucagon is a hormone that increases blood glucose levels when they drop too low (e.g., during fasting).
The pancreas detects low blood glucose using specialized alpha cells.
Alpha cells (not beta cells) in the pancreas secrete glucagon as a response.
Glucagon targets the liver, not the muscles, to release stored glucose.
Muscles do not release their stored sugar because they need energy for constant function.

Stimulus: a decrease in blood glucose level is detected by the pancreas.
The pancreas acts as both the receptor and control center.
Alpha cells secrete glucagon, which is carried to the liver.
In the liver, glucagon triggers the conversion of glycogen (stored sugar) into glucose (usable sugar).
Glucose is released into the bloodstream, raising blood glucose levels back to normal.

Once blood glucose returns to normal, glucagon secretion decreases.
This prevents excessive use of stored glycogen, maintaining glucose balance (homeostasis).
The system works through negative feedback: increases and decreases in hormone levels to keep balance.

Always state the change in glucose levels when answering related questions.
Only the liver (not muscles) releases stored sugars in response to glucagon.
Glucagon and insulin are antagonistic hormones—they have opposite effects on blood glucose.

Glucagon — hormone produced by alpha cells that raises blood glucose by converting liver glycogen to glucose.
Glycogen — stored form of glucose in the liver.
Alpha cells — pancreatic cells that detect low glucose and secrete glucagon.
Insulin — hormone produced by beta cells to lower blood glucose.
Negative feedback — a control system that reduces hormone secretion once normal conditions are restored.
Antagonistic hormones — hormones with opposite effects (e.g., insulin vs. glucagon).