Controlling blood glucose (how much sugar is in the blood) is very important in the body. If our blood sugar levels get out of control this can lead to serious short term problems such as hypoglycemia (low blood sugar), hyperglycemia (high blood sugar) or diabetic ketoacidosis. In the long term is can also damage vessels that supply blood to important organs like the heart, kidneys, eyes and nerves.
So basically it’s really, really important!
So how does the body control blood glucose I hear you ask, well, it’s all down to a little thing called insulin.
Insulin is a hormone that works to decrease the concentration of glucose in the blood. It does this by increasing the number of glucose carrier proteins in the plasma membranes of some cells. (More glucose will be taken up from the blood into cells and so the concentration of the glucose in the blood decreases).
Insulin binds to the receptors on the cell membrane of cells. When insulin binds to the receptor it causes blood glucose concentration to decrease. One way it can do this is by activating enzymes involved with converting glucose into fat and glycogen.
Insulin comes from the Islets of Langerhans found in the pancreas. There are two types of cells in the Islets of Langerhans. The alpha cells secrete glucagon and beta cells secrete insulin.
However, some people are unable to produce enough insulin, this causes someone to suffer from diabetes.
There are two main types of diabetes. Type two is insulin independent. Here insulin no longer has an effect on the uptake of glucose by cells in the body.
Type two diabetes is often controlled by insulin injections. Insulin cannot be taken as a tablet as it is a protein and so will be broken down by enzymes in the stomach and the small intestine.
Type one is often due to a response where the body attacks its own beta cells in the pancreas. These are the cells responsible for producing insulin.
On the opposite side of the spectrum what happens to the body when the blood sugar levels are too low?
Well, a hormone called glucagon works to increase the concentration of glucose in the blood. Glucagon is released from the alpha cells in the Islets of Langerhans. The Islets of Langerhans are found in the pancreas.
The process of breaking down glycogen into glucose is called glycogenolysis. Glycogen stores are found in the liver and skeletal muscle.
By increasing the rate of respiration, the concentration of glucose in the blood decreases. Glucose is the main respiratory substrate in cells. Increasing the respiratory rate will increase the amount of glucose used, and so the concentration of glucose in the blood decreases.
Adrenaline can reduce the activity of enzymes that turn glucose into glycogen. Adrenaline is part of the flight or fight response. Glucose is needed for respiration, and so turning it to glycogen could limit the amount of energy available to the body.
The secondary messenger that adrenaline binds to in a cell is cAMP. ATP is converted to cyclic AMP which can then act as a secondary messenger. Both glucagon and adrenaline act using this secondary messenger.