Regulation of blood sugar levels in the body is a preserve of the endocrine system. The endocrine system of the body is the group of glands that produce hormones which regulate various processes of the body including blood sugar levels.
During increase in blood sugar, the pancreas secretes insulin, a hormone produced by the beta cells in this gland. Insulin causes the fat cells, muscle cells and red blood cells to absorb sugar from the blood.
During decrease in blood sugar levels, the pancreas again secretes glucagon from its alpha cells. Glucagon stimulates the liver to release the glucose stored in its cells.
The adrenal gland also responds to low blood sugar levels by secreting cortisol which promotes the use of fatty acids to provide energy for working muscles rather than use glucose.