THE ACTIONS OF GLUCAGON AND INSULIN

 

Introduction: Glucagon is a peptide hormone, and is one of the hormones produced by α cells of the pancreas from one of the divisions known as the endocrine pancreas.  Glucagon works to raise the concentration of glucose in the bloodstream from the liver and skeletal muscles, as the opposite step accomplished by Insulin, which lowers the glucose levels in blood and initiates it's storage for later use. 

Mechanism of Glucagon production:  The pancreas releases glucagon when the concentration of glucose in the bloodstream falls too low to sustain cellular respiration. This is especially true between meals, or during starvation.  Glucagon causes the liver to convert stored glycogen into glucose, which is released into the bloodstream in situations of lower than normal blood glucose. 

In a negative feedback mechanism, high blood-glucose levels stimulate the release of insulin from the endocrine pancreas. 

[glycogen] [insulin] [glucose] [carbohydrates] [negative feedback mechanism]  

Insulin:  Insulin allows glucose to be taken up and used by insulin-dependent tissues. Thus, glucagon and insulin are part of a feedback system that keeps blood glucose levels at a stable level. It increases energy expenditure and is elevated under conditions of stress. Glucagon generally elevates the concentration of glucose in the blood by promoting gluconeogenesis and glycogenolysis. 

[gluconeogenesis] 

Storage and release of Glucose:  Glucose is stored in the liver in the form of the polysaccharide glycogen, which is a glucan, which is a polymer made up of glucose molecules. Liver cells also known as hepatocytes, have glucagon receptors. When glucagon binds to the glucagon receptors, the liver cells convert the glycogen into individual glucose molecules and release them into the bloodstream, in a process known as glycogenolysis. 

As these stores become depleted, glucagon then encourages the liver and kidney to synthesize additional glucose by gluconeogenesis. Glucagon turns off glycolysis in the liver, causing glycolytic intermediates to be shuttled to gluconeogenesis. Glucagon also regulates the rate of glucose production through lipolysis. Glucagon induces lipolysis in humans under conditions of insulin suppression such as diabetes mellitus type 1.

RELATED;

1.  INSULIN  

2.  CARBOHYDRATES

3. THE ENDOCRINE PANCREAS

REFERENCES