Control of blood glucose levels

The conc. of blood glucose levels in blood is 90mg per 100ml of blood. Despite what you eat or you don’t, it will always stay the same. This is achieved by negative feedback. Blood glucose levels are controlled by islets of langerhans (endocrine gland portion of the pancreas) and secrete glucagon to raise glucose levels in blood and insulin to lower glucose levels.

Glucose levels too high:-

  1. Islets of Langerhans monitor blood glucose levels.
  2. Alpha cells cease to secrete their hormone glucagon .
  3. Beta cells secrete their hormone insulin in to the blood.
  4. Insulin binds to a complementary protein receptor- this is an example of cell signalling(important that you know this). This acts as the 1st messenger, sometimes referred to a 1ry messenger.
  5. The cells that it activates are G-protein coupled receptors (GPCR’s).
  6. Next, alpha subunit dissociates from the trimeric G-protein(Beta and Gamma subunits still attached to each other) and activates adenyl cyclase.(sometimes, this enzyme is referred to adenylyl cyclase or adenylate cyclase)
  7. Now, this catalyses a reaction. This enzyme converts ATP to cyclic AMP. This acts as the 2nd messenger or sometimes referred to a 2ndry messenger
  8. So cells respond

What effect it produces:-

We need more glucose into the cells, as glucose concentration is above the threshold level as well as it being above the renal threshold. This causes a lot of health problems e.g. renal failure.So , we need more glucose uptake. The effector/target organs are the liver and the muscle. Sometimes, the brain is involved.

  1. After 1st and 2nd messenger activity, we get more glucose channel proteins. So, glucose will enter by facilitated diffusion.
  2. Also we get the activation of glycogen synthetase. This, as the name suggests converts glucose to glycogen. So, this is an example of a condensation reaction. This reaction is also called glycogenesis
  3. Thirdly, we are going to get more respiration. This is not breathing in an out. Instead, the respiration of glucose ( the respiratory substrate) is converted into ATP by the glycolytic pathway, krebs cycle and oxidative phosphorylation. This is because NADred and FADred have been made-so there is a lot of reducing power. So therefore, more glucose is used, hence glucose conc. drops.

Glucose is too low:-

  1. Islet cells monitor glucose levels.
  2. Beta cells no longer secrete their hormone insulin
  3. Alpha cells secrete their hormone glucagon
  4. Same cell signalling methods described above occur.
  5. Target is the liver cells
  6. You will get glycogenolysis. This is because of the activation of glycogen phosphorylase. As the name of the enzyme implies, glycogen is converted in to load of glucose molecules, hence an increase conc. Of glucose in blood
  7. You will get also gluconeogenesis. This occurs in the kidney. This is when fatty acids and amino acid both containing carbon, hydrogen and oxygen get converted into glucose.hence an increase conc. Of glucose in blood
  8. Also because of the lack of insulin, you will get less respiration and less glucose uptake.