Regulation of Blood Glucose

The Pancreas has both endocrine and exocrine functions

Exocrine Function:

• Enzymes- amylase (carbohydrase), Trypsinogen (inactive protease) and lipase
• Sodium hydrogen carbonate- neutralises stomach contents
• Mix exits pancreas via pancreatic duct joins bile duct and is secreted ino the duodenum (top of small intestine)

Endocrine Function:

• Islets of langerhans are group of cells
• Alpha cells manufacture and secrete glucagon
• Beta cells manufacture and secrete insulin
• The are secreted directly into the blood (capillaries)

If blood glucose concentration is too high (above 90 mg per 100cm-3)

1) cell membranes of beta cells have K+ and Ca 2+ ion channels- at a resting potential of -70mV potassium ion channels are open and calcium ion channels are closed.

2) When glucose concentrations are too high, glucose molecules diffuse into cell

3) Glucose is quickly converted into ATP

4) Extra ATP causes potassium ion channels to close, potassium ions cannot diffuse out, altering potential difference of cell membrane (inside becomes less negative)

5) The change in potential difference causes the calcium ion channels to open, calcium ions enter cells.

6) The calcium ions entering causes the secretion of insulin by making vesicles containing insulin be released via exocytosis.

7) Insulin travels in blood to target cells- hepatocytes,muscle cells, and brain cells-binds to receptor on cell surface membrane, activates a second messenger system inside cell which activates a series of enzyme controlled reactions:

• More glucose enters cells via glucose channels
• Glucose is converted to glycogen (glycogenesis) for storage
• More glucose is coverted to fats
• More glucose used in respiration

1) Alpha cells detect this and manufacture and secrete glucagon into the blood

2) Travels to receptor sites on target cells and binds.

3) Initiates following reactions:

• Conversion of glycogen to glucose- glycogenolysis
• Use of more fatty acids is respiration
• Production of glucose from conversion of amino acids and fats-glyconeogenesis