Glucose Homeostasis: Regulation of Blood Glucose

After eating, high blood glucose levels stimulate insulin secretion from the pancreas. Insulin inhibits hepatic glucose production and stimulates glucose uptake and metabolism by muscle and adipose tissue. Excess glucose is converted into glycogen and stored in the liver and muscles for later use during fasting.

During fasting, when blood glucose levels drop, the pancreas secretes glucagon. In the liver, glucagon stimulates glucose production via gluconeogenesis and glycogenolysis, raising blood glucose back to normal levels. This counterbalances insulin's effects to maintain stable glucose homeostasis throughout the fasting period.

Insulin and glucagon work in a reciprocal manner to regulate blood glucose. When glucagon levels rise during fasting, the body counteracts by releasing insulin when glucose becomes available. This hormonal cycle ensures blood glucose remains stable whether the body is fed or fasting, maintaining energy balance and metabolic function.

During exercise, catecholamines stimulate hepatic glucose production, inhibit insulin secretion, and enhance glucagon release. These coordinated hormonal changes increase glucose availability to working muscles while preventing hypoglycemia. This ensures sufficient energy supply during physical activity and maintains stable blood glucose levels.

Excess glucose consumed after meals is converted into glycogen and stored in the liver and muscles. Glycogen serves as a readily available energy reserve during fasting or between meals. This storage mechanism allows the body to maintain stable blood glucose levels and provide sustained energy throughout the day.

During fasting, the liver produces glucose through two pathways: gluconeogenesis, which creates new glucose from non-carbohydrate sources, and glycogenolysis, which breaks down stored glycogen. Glucagon stimulates both pathways to restore blood glucose levels when dietary glucose is unavailable, maintaining energy homeostasis.

In the prandial state after eating, high blood glucose stimulates insulin secretion, promoting glucose uptake and storage as glycogen. During fasting, low blood glucose triggers glucagon secretion, stimulating glucose production through gluconeogenesis and glycogenolysis. These opposing hormonal responses maintain glucose homeostasis across different metabolic states.