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Diabetes: physiology

Watch Dan explain the main functions of insulin and how insulin is normally released from the pancreas.
DANIEL MALONE: In this section, you’ll see what the main functions of insulin are and how insulin is normally released from the pancreas. Insulin is a hormone that is secreted from the pancreas when blood sugar levels are high. The pancreas sits next to the small intestine, under the liver. Insulin is secreted by the pancreas after we have a meal and in response to high blood sugar levels. So the more sugar we have, the more insulin is released. The term “sugar” refers to many different compounds that are sweet and found in different foods. The main sugar regarding diabetes is glucose. Other sugars include fructose and lactose, but these sugars do not trigger insulin release.
Insulin is released into the bloodstream and travels around the body to increase the amount of glucose entering the body’s cells. Once in cells, particularly in the liver, glucose is stored as glycogen for later use. Insulin also increases glycogen being made from glucose in cells such as hepatocytes in the liver and in muscle tissue. Insulin also decreases the breakdown of glycogen into glucose and decreases the glucose being made from other sources in the body such as facts. So over all, insulin reduces the amount of glucose in the blood.
In people with type II diabetes such as Shirley, not only is there less insulin released from the pancreas, the insulin that is released is not able to reduce the amount of blood glucose by these mechanisms as efficiently. Firstly, let’s look at what normally produces insulin to be secreted from the pancreas. This is a pancreatic B cell. The pancreatic B cell’s main function is to produce and secrete insulin into the bloodstream. As you can see, B cells have potassium channels called KATP channels. When the potassium channels open potassium can leave the cell. When a person eats a meal, glucose from the blood is taken up by the B cells in an active transport fashion.
Active transport means the glucose is actively pumped into the cells. Glucose is broken down inside the B cell, and after a number of steps, ATP or adenosine triphosphate is produced. ATP is an important energy source for many cells in the body. In B cells, after ATP is produced from glucose it binds to KATP channels, which is so called because ATP binds to them. The KATP channels close in response to ATP binding. Since potassium is continually being pumped into cells via our potassium pump, closing of the KATP channels results in an increased concentration of potassium in the B cells, and this changes the charge of the cell.
Since calcium channels are sensitive to changes in charge, calcium channels open and this means calcium ions rush into the cell. And it is this increase in intracellular calcium in the B cells that triggers vesicles or little sacs full of insulin to move to the cell membrane and release insulin.
The released insulin then enters the bloodstream.
So in summary, glucose is pumped into the B cell, is made into ATP. ATP binds to the KATP channels and causes them to close, leading to an increase in potassium, which triggers calcium channels open, and calcium rushes into the cell. And this is the trigger for insulin to be released into the bloodstream. In type II diabetes there is impaired insulin secretion from the pancreas. So in this section, you saw how insulin is extremely important in reducing blood glucose, mainly by promoting its uptake and storage in cells and the process by which insulin is normally released from the pancreas.

Watch Dan explain the main functions of insulin and how insulin is normally released from the pancreas.

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The Science of Medicines

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