#InsulinAndGlucagon

#Biology

#EndocrineSystem

Introduction

• Insulin and glucagon are hormones that help regulate the levels of blood glucose — aka sugar — in your body. Glucose comes from the food you eat and moves through your bloodstream to help fuel your body.

  ○ Insulin controls whether sugar is used as energy or stored as glycogen.

  ○ Glucagon signals cells to convert glycogen back into sugar.

• Insulin and glucagon work in what’s called a negative feedback loop. During this process, one event triggers another, which triggers another, and so on, to keep your blood sugar levels balanced.

• Insulin lowers your blood sugar level. Glucagon (another hormone) naturally raises it. Your body uses these two hormones to balance out your blood sugar level to keep it in a healthy range. If you have diabetes, too much (manufactured) insulin can lead to low blood sugar (hypoglycemia).

How insulin works

• During digestion, foods that contain carbohydrates are converted into glucose. Most of this glucose is sent into your bloodstream, causing a rise in blood glucose levels, which signalsTrusted Source your pancreas to produce insulin.

• The insulin tells cells throughout your body to take in glucose from your bloodstream. As the glucose moves into your cells, your blood glucose levels go down.

• Some cells use glucose as energy. Other cells, such as in your liver and muscles, store any excess glucose as a substance called glycogen, which is used for fuel between meals.

• Beta cells identify high blood sugar concentrations primarily through the phosphorylation of glucose via high-affinity glucokinase, which occurs when glucose levels exceed 2.5 mmol/l.

• Rising blood glucose levels increase oxidative metabolism in beta cells, resulting in a higher ATP/ADP ratio, which triggers insulin secretion.

• Pancreatic beta cells sense higher ATP levels through the ATP-sensitive K+ (KATP) channels in their plasma membrane.

• Insulin opens cells by binding to receptors on the cell's surface, which causes glucose transporter proteins (GLUT4) to move to the cell's surface. GLUT4 molecules then act as vehicles to transport glucose into the cell.

How glucagon works

• Glucagon works to counterbalance the actions of insulin.

• About 4–6 hours after you eat, the glucose levels in your blood decrease. This triggers your pancreas to produce glucagon.

• This hormone signals your liver and muscle cells to convert the stored glycogen back into glucose. These cells then release the glucose into your bloodstream so your other cells can use it for energy.

• This whole feedback loop with insulin and glucagon is constantly in motion. It keeps your blood sugar levels from dipping too low, ensuring that your body has a steady supply of energy.

• Upon glucagon stimulation, activated PKA phosphorylates glycogen phosphorylase kinase, which phosphorylates serine-14 residue of glycogen phosphorylase.

• This activated glycogen phosphorylase phosphorylates glycogen, resulting in increased glycogenolysis and the production of glucose-6-phosphate.