フィードバックループ

Negative feedback is a regulatory loop that prevents excessive hormone production. It begins when a stimulus triggers hormone release to maintain a specific level. Once that level is reached, the hormone signals the body to stop further production, creating a self-limiting cycle that maintains hormonal balance through the endocrine system.

When blood glucose rises, the pancreas releases insulin, which stimulates cells to take up glucose for energy and converts excess glucose to glycogen in the liver. These actions lower blood glucose levels, which then signals the pancreas to stop producing insulin through negative feedback regulation.

During low blood glucose, alpha cells of the pancreas release glucagon, which converts stored glycogen in the liver back to glucose for cellular energy use. Glucagon also stimulates the liver to convert amino acids into glucose, raising blood glucose levels until negative feedback signals the pancreas to stop glucagon release.

Hormone production is regulated by other hormones, nervous system activation, and humoral stimuli—concentration changes in extracellular fluids like blood. These regulatory factors work together to control when and how much hormone is released, maintaining physiological balance through mechanisms like negative feedback.

Insulin and glucagon function as opposing hormones in a balanced feedback system. Insulin lowers blood glucose by promoting glucose uptake and storage, while glucagon raises it by converting glycogen to glucose. Each hormone's action triggers negative feedback that inhibits the other, maintaining stable blood glucose levels.

Negative feedback prevents excessive hormone levels by creating a self-regulating cycle where the hormone's effect triggers signals to stop its own production. This mechanism maintains hormonal homeostasis, ensuring the body produces only the amount of hormone needed to respond to a stimulus without overshooting.

High blood glucose stimulates pancreatic beta cells to release insulin. Insulin enables glucose uptake and storage, lowering blood glucose back to normal levels. This decrease in glucose concentration signals the pancreas to cease insulin production, completing the negative feedback loop and restoring hormonal balance.