What is insulin ?
Insulin is a peptide hormone produced by beta cells present in
langerhans islets in pancreas
Chemistry of insulin
Insulin is a small peptide (protein) consisting of
fifty-one amino acids synthesized and stored within
The protein itself consists of two chains, denoted
A and B, linked by disulfide (sulfur-sulfur) bridges
between cysteine residues
Summary of how insulin works
Elevated levels of glucose in the blood stimulates cells of
the pancreas to increase insulin secretion into the blood.
The insulin circulates the body, and within
minutes, stimulates the liver and muscle cells to take up
glucose from the blood. As glucose is removed from the
blood, obviously blood levels fall.
Let’s take a closer look at what is happening
Blood glucose level is monitored by the beta cells of the pancreas, and
when levels rise above about 90 mg/dl, the pancreas begins to secrete an
increased amount of insulin.
The higher the sugar levels, the more insulin is released.
The insulin is carried in the blood plasma bound to beta-globulin.
Globulins are just large proteins found in the blood, and the alpha & betaglobulins carry hormones, lipids, vitamins e.t.c. around the body.
There are “receptor sites” on the cell membranes of liver & muscle cells,
and the insulin binds to these receptors.
This causes the cells to become more permeable to glucose, as well as
activating some enzyme systems within the cells.
Other substances known to stimulate insulin release
include :Amino acids from ingested proteins, Three amino
acids (alanine, glycine and arginine) act similarly to
glucose by altering the beta cell's membrane potential.
Acetylcholine released from vagus nerve endings
Gastrointestinal hormones released by
enteroendocrine cells of intestinal mucosa and
Glucose-dependent insulinotropic peptide (GIP).
Insulin modulates NT levels such
as dopamine and acetylcholine
excess insulin cause excess
glucose uptake leading to
liberation of free radicals after
breakdown of glucose
Due to destruction of
cells by free radicals
Insulin is a fat sparer causing
And decrease vessel
diameter leading in ^BP
INHIBITORS OF INSULLIN SECRETION
HORMONES ANTAGONIST TO INSULIN
(and Growth Hormone)
Half life of insulin is about 6 minutes
So it is cleared off from circulation within 10 -15 mins
except that has combined with receptors
The remainder is degraded by enzyme INSULINASE
mainly in liver