Final answer:
Insulin lowers blood glucose levels by promoting glucose uptake and storage, while glucagon raises blood glucose levels by stimulating glycogen breakdown and glucose production. Together, they regulate glucose homeostasis, especially during variations in energy demand such as exercise or fasting.
Step-by-step explanation:
The role of insulin and glucagon in controlling blood glucose levels involves their opposing actions. Insulin, which is released from the beta cells of the pancreas when blood glucose levels are high, primarily lowers blood glucose levels by promoting glucose uptake into cells, such as liver and muscle cells, and converting glucose into glycogen for storage. It also stimulates the conversion of glucose to fat in adipose cells and inhibits glucose production in the liver.
On the other hand, glucose is secreted by the alpha cells of the pancreas when blood glucose levels are low. It raises blood glucose levels by stimulating the breakdown of glycogen back into glucose in the liver and muscles, a process known as glycogenolysis, and by promoting the production of glucose through gluconeogenesis.
During exercise or fasting, when glucose is rapidly utilized, glucagon helps to maintain blood glucose levels by these processes. Thus, insulin and glucagon work together to maintain glucose homeostasis, with insulin activated in times of high blood sugar and glucagon in times of low blood sugar.