The body manufactures insulin in the pancreas, and the hormone is secreted by its beta cells, primarily in response to glucose.
The beta cells of the pancreas are perfectly designed "fuel sensors" stimulated by glucose.
As glucose levels rise in the plasma of the blood, uptake and metabolism by the pancreas beta cells are enhanced, leading to insulin secretion.
Insulin has two modes of action on the body - an excitatory one and an inhibitory one:
- Insulin stimulates glucose uptake and lipid synthesis
- It inhibits the breakdown of lipids, proteins and glycogen, and inhibits the glucose pathway (gluconeogenesis) and production of ketone bodies (ketogenesis).
What is the pancreas?
The pancreas is responsible for controlling the body's sugar levels and sits near the stomach in the abdomen.
The pancreas is the organ responsible for controlling sugar levels. It is part of the digestive system and located in the abdomen, behind the stomach and next to the duodenum - the first part of the small intestine.
The pancreas has two main functional components:
- Exocrine cells - cells that release digestive enzymes into the gut via the pancreatic duct
- The endocrine pancreas - islands of cells known as the islets of Langerhans within the "sea" of exocrine tissue; islets release hormones such as insulin and glucagon into the blood to control blood sugar levels.
Islets are highly vascularized (supplied by blood vessels) and specialized to monitor nutrients in the blood. The alpha cells of the islets secrete glucagon while the beta cells - the most abundant of the islet cells - release insulin.
The release of insulin in response to elevated glucose has two phases - a first around 5-10 minutes after glucose levels are raised and a second after 30-60 minutes.
How does insulin regulate glucose?
Glucose levels are tightly controlled by insulin so that the rate of glucose production by the liver is matched by the rate of use by the cells. In diabetes, hyperglycemia means that the loss of glucose through the urine is also needed to achieve this balance.
In healthy individuals, the role of insulin is to keep a steady blood glucose level by ensuring sufficient release from the liver. Low insulin levels cause the release of glucose while more insulin inhibits glucose production by telling the liver to store glucose as glycogen.
The importance of insulin for maintaining blood glucose levels is mainly due to this effect on liver storage and release. The uptake of glucose by cells can take place without insulin - the hormone simply accelerates this uptake through recruitment of glucose transporter molecules to the cell membrane.
If there is a lack of insulin in the liver, the liver releases glucose into the bloodstream faster than tissues can metabolize it.