Blood sugar levels are regulated by
negative feedback in order to keep the body in
balance. The levels of
glucose in the blood are monitored by many tissues, but the cells in the
pancreatic islets are among the most well understood and important. Granule docking is an important glucose-dependent step in human insulin secretion that does not work properly in
type 2 diabetes.
Glucagon If the blood glucose level falls to dangerously low levels (as during very heavy exercise or lack of food for extended periods), the
alpha cells of the pancreas release
glucagon, a peptide
hormone which travels through the blood to the liver, where it binds to
glucagon receptors on the surface of liver cells and stimulates them to break down
glycogen stored inside the cells into glucose (this process is called
glycogenolysis). The cells release the glucose into the bloodstream, increasing blood sugar levels.
Hypoglycemia, the state of having low blood sugar, is treated by restoring the blood glucose level to normal by the ingestion or administration of
dextrose or
carbohydrate foods. It is often self-diagnosed and self-medicated orally by the ingestion of balanced meals. In more severe circumstances, it is treated by injection or infusion of glucagon.
Insulin When levels of blood sugar rise, whether as a result of
glycogen conversion, or from digestion of a meal, a different hormone is released from
beta cells found in the
islets of Langerhans in the pancreas. This hormone,
insulin, causes the liver to convert more glucose into glycogen (this process is called
glycogenesis), and to force about 2/3 of body cells (primarily
muscle and fat tissue cells) to take up glucose from the blood through the
GLUT4 transporter, thus decreasing blood sugar. When insulin binds to the receptors on the cell surface, vesicles containing the GLUT4 transporters come to the plasma membrane and fuse together by the process of
endocytosis, thus enabling a facilitated diffusion of glucose into the cell. As soon as the glucose enters the cell, it is phosphorylated into
glucose-6-phosphate in order to preserve the concentration gradient so glucose will continue to enter the cell. Insulin also provides signals to several other body systems, and is the chief regulator of metabolic control in humans. There are also several other causes for an increase in blood sugar levels. Among them are the 'stress' hormones such as
epinephrine (also known as adrenaline), several of the steroids, infections, trauma, and of course, the ingestion of food.
Diabetes mellitus type 1 is caused by insufficient or non-existent production of insulin, while type 2 is primarily due to a decreased response to insulin in the tissues of the body (
insulin resistance). Both types of diabetes, if untreated, result in too much glucose remaining in the blood (
hyperglycemia) and many of the same complications. Also, too much insulin and/or exercise without enough corresponding food intake in diabetics can result in low blood sugar (
hypoglycemia). ==Hormones that influence blood glucose level==