Insulin is a small hormone responsible for reducing blood sugar levels.
For an overall view of how blood glucose is regulated, see my article “How the body regulates blood sugar levels”. This article is more specifically about the actions of insulin, is a little more technical, and goes into a little more details of how insulin works to bring about a reduction in blood sugar levels.
Summary of how insulin works
Elevated levels of glucose in the blood stimulates cells of the pancreas to increase insulin secretion into the blood. The insulin circulates the body, and within minutes, stimulates the liver and muscle cells to take up glucose from the blood. As glucose is removed from the blood, obviously blood levels fall. As the levels in the blood fall, the secretion of insulin falls to, so less is produced, and less is taken up by the liver and muscle. In this way, the blood glucose level is reduced back to within the normal range.
Let’s take a closer look at what is happening
Blood glucose level is monitored by the beta cells of the pancreas, and when levels rise above about 90 mg/dl, the pancreas begins to secrete an increased amount of insulin. The higher the sugar levels, the more insulin is released.
The insulin is carried in the blood plasma (which is the term given to the liquid part of the blood and its the plasma that carries the blood cells around) bound to beta-globulin. Globulins are just large proteins found in the blood, and the alpha & beta-globulins carry hormones, lipids, vitamins e.t.c. around the body.
There are “receptor sites” on the cell membranes of liver & muscle cells, and the insulin binds to these receptors. This causes the cells to become more permeable to glucose, as well as activating some enzyme systems within the cells. These changes lead to:
- Increased Glycogenesis – the conversion of glucose to glycogen in liver and muscles.
- Increased Glucose uptake by the cells.
- Increased use of glucose for energy rather than fats or other energy stores.
- Increased production of fats (and fat deposition) from the excess glucose.
- Decreased Gluconeogenesis – the production of glucose from non-carbohydrate sources. Gluconeogenesis usually occurs in the hypoglycaemic state, which stimulates the sympathetic nervous system to release adrenaline (which itself stimulates the conversion of stored glycogen into free glucose). In extreme cases of hypoglycaemia, proteins in the body will be broken down and converted to glucose for energy. Obviously this is a very bad state to be in, as your body can start to eat your own muscle.
A note about synthetic Insulins
If you do any research on the internet, you'll probably hear about Humalog, a synthetic insulin mimic. It is often called by a number of other names including lispro Humalog insulin. Interestingly, this mimic is not identical to human insulin. Scientists found that by swapping a couple of amino acids on the b-chain of the molecule – namely Lysine and Proline (hence the name), they could get the same effect, but because the insulin was absorbed much faster, it acted more quickly offering a range of benefits to diabetics. Another insulin mimic that works in a similar way to Humalog, is Novolog.