Homeostasis can be defined as an organism's tendency to maintain the equilibrium of different internal systems by using various biochemical and physical processes. Examples of homeostasis in humans include the body's attempt to maintain a fairly constant and normal blood pressure, and its efforts to regulate internal body temperature. Another example of human homeostasis is glucose homeostasis, also known as blood glucose regulation or blood sugar regulation. Glucose homeostasis relies on the balance and interactions of two hormones — insulin and glucagon — to maintain a healthy blood glucose level.
Under normal circumstances, the body is able to balance the amount of glucose, or sugar, in the blood with the amount of glucose that the cells need for fuel. The hormone insulin, which the pancreas produces, facilitates the transport of glucose into the cells. Too little available insulin in the bloodstream will reduce the amount of glucose that the cells are able to absorb. This will raise the blood glucose level, which in turn stimulates the pancreas to release more insulin and allow more glucose absorption.
The other side of the equation in glucose homeostasis involves glucagon — another hormone produced by the pancreas. Glucagon works in a similar but opposite manner as insulin. When blood glucose levels are low, the pancreas releases glucagon. The hormone stimulates the liver to release glucose stored within its cells, thus raising blood glucose levels to a normal level.
In a healthy individual, these hormonal interactions and adjustments maintain a fairly constant and optimal blood glucose level. When something interrupts this glucose homeostasis, a person may experience blood glucose levels outside the normal range for a healthy person. Hyperglycemia, or high blood glucose, can occur when the pancreas produces insufficient insulin or when cells are resistant to insulin.
Insufficient insulin and insulin resistance are associated with diabetes mellitus and can cause severe hyperglycemia. Patients with diabetes mellitus should closely monitor their blood glucose levels. Often, individuals with diabetes will need to take insulin injections or oral medications to control their high blood glucose. Left untreated, diabetes mellitus and the associated hyperglycemia can damage the kidneys, eyes, and circulatory system.
Hypoglycemia, or low blood glucose, is typically considered less serious than hyperglycemia unless the hypoglycemia is present in a patient with diabetes. In such cases, the hypoglycemia can mean an overdose of administered insulin or oral medication, which can lead to dangerously low blood glucose levels. Less serious cases can occur because of fasting, overexertion, or some metabolic condition. Symptoms of hypoglycemia include fatigue, nausea, and dizziness.