Effects of Insulin and Glycogen

Summary of the action of insulin and glycogen in the body

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  • Created on: 28-02-11 16:44
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Hormones Revision:
The Pancreas:
Has both an exocrine and an endocrine function:
Exocrine ­ This is a gland that secretes chemicals into a duct. Acinar cells in the pancreas secrete
pancreatic juice into the pancreatic duct. The pancreatic juice contains many enzymes, including
trypsin, lipase and amylase to help break down food. The pancreatic duct leads to the duodenum
(part of the small intestine).
Endocrine ­ This is the gland that secretes hormones directly into the blood. The Alpha and Beta cells
in the Islets of Langerhans secrete Glucagon and Insulin respectively. Alpha cells are round the
outside, with Beta cells in the centre of the Islets of Langerhans.
The Action of Insulin on a cell:
The Insulin binding to receptors in a cell membrane cause vesicles containing GLUT4 transporter
proteins to merge with the plasma membrane. This means that Glucose molecules can diffuse into
cells, down their concentration gradient, using the GLUT4 transporter proteins. This helps lower the
blood glucose levels in the body.
Glycogenesis = formation of Glycogen from Glucose catalysed by Insulin.
Insulin molecules arrive at the receptors on the surface of hepatocytes, which activates Glucokinase
(an enzyme). Glucokinase causes Glucose molecules to be phosphorylated, trapping the glucose
inside the cell as phosphorylates glucose cannot pass back through the GLUT4 transporter proteins in
the cell membrane.
Insulin activates Glycogen Synthase and Phosphofructokinase, which condense the phosphorylated
glucose molecules, forming alpha 1-4 glycosidic bonds. This is Glycogen!
Glycogenolysis = The breakdown of Glycogen into Glucose catalysed by Glucagon.
The release of Glucagon inhibits the release of Insulin (and vice versa)
Glucagon activates the enzymes needed for the breakdown of glycogen into glucose
This will stimulate the uptake of amino acids and glycerol into the liver, where glycogen is
converted to glucose.
Gluconeogenesis = The production of Glucose from scratch using body fat and muscles.


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