Control of Blood Glucose Concentration
- Factors that affect glucose concentration are food, medication, activity, biological, environmental and many more.
Insulin is released from the beta cells of the islets of Langerhans in the pancreas when high levels of glucose are detected.
It binds insulin receptors of the liver which stimulates the conversion of glucose to glycogen (glycogenesis) and glucose to fat. This causes the level of glucose to drop.
If the blood glucose concentration becomes too low, it is detected by the alpha cells of the islets of Langerhans in the pancreas.
These produce glucagon which binds to receptors of the liver cells.
This stimulates the conversion of glycogen to glucose (glycogenolysis) and using other biological molecules such as amino acids and glycerol to convert them into glucose (gluconeogenesis).
This whole process is known to be multiple feedback as the levels of glucose fluctuate around the normal level.
Insulin also binds to insulin receptors of body cells.
This increases the rate of absorption of glucose into the body cells particularly muscle cells and is used for respiration.
- The adrenal glands are found on top of each kidney and it consists of the adrenal cortex and adrenal medulla.
(1) Adrenal cortex - This releases cortisol which is secreted when glycogen stores run out. It stimulates gluconeogenesis which increases glucose levels quickly.
(2) Adrenal medulla - This releases adrenaline and causes glycogenolysis.
- Adrenaline, the first messenger, binds to receptors on the cell surface membrane to create hormone-receptor complex.
- The formation of the complex causes the enzyme adenylate cyclase/adenylyl cyclase to be activated.
- It catalyses the conversion of ATP into cyclic AMP which is the second messenger.
- Cyclic AMP activates an enzyme, Protein Kinase A/Protein Kinase, in the cell which starts a cascade of reactions.
- The last reaction to occur is the conversion of glycogen into glucose (glycogenolysis).
- Diabetes is a disorder where the blood glucose levels are not regulated properly.
(1) Type 1/insulin-dependent
- This occurs suddenly in childhood.
- The body is unable to produce any insulin and is thought to be because the beta cells of the islets of Langerhans in the pancreas have been targeted by the immune system.
- The levels of glucose can be controlled by regular injections with insulin and the careful management of diet and exercise.
(2) Type 2/insulin-independent
- This occurs mainly in people over the age of 40 however it is becoming increasingly more common in adolescents too.
- This condition arises when the insulin receptors are no longer responsive to insulin or an inadequate amount of insulin is being made by the beta cells.
- This can be controlled by the careful management of diet and exercise.
That's the end of the topic!
Drafted by Bonnie (Biology)