Coupon Accepted Successfully!


Insulin and Glucagon

Pancreatic Cell
α cells
β cells (most common 60-75%)
F cells
Pancreatic Polypeptide
D1 cells
Epsilon cells
  1. Insulin is a polypeptide anabolic hormone containing two chains of amino acids linked by disulfide bridges
  2. Insulin secretion begins at 12 weeks.
  3. Beef insulin differs by three amino acids from a human, Pork insulin differs from human insulin by only one amino acid.
  4. Insulin is synthesized in the rough endoplasmic reticulum of the B cells. It is then packaged in Golgi apparatus and expelled by exocytosis.
  5. Insulin is synthesized as part of a larger preprohormone. The gene for insulin is located on the short arm of chromosome 11 in humans.
  6. Preproinsulin has a 23-amino-acid signal peptide removed as it enters the endoplasmic reticulum. The remainder of the molecule is then folded, and the disulfide bonds are formed to make proinsulin.
  7. The peptide segment connecting the A and B chains, the connecting peptide (C peptide), facilitates the folding and then is detached in the granules before secretion.
  8. Normally, 90–97% of the product released from the B cells is insulin along with equimolar amounts of C-Peptide
1. peptide.
  1. C-peptide level in blood provides an index of B cell function in patients receiving exogenous insulin.
  2. The half-life of insulin in the circulation in humans is about 5 min
  3. The normal concentration of insulin in fasting normal humans is 0–70 U/mL. The amount of insulin secreted in the basal state is about 1 U/h, with a fivefold to tenfold increase following ingestion of food. The average amount secreted per day in a normal human is about 40 U.
GLUT Transporter for facilitated diffusion of glucose
  GLUT 1 Basal glucose uptake Placenta, blood-brain barrier, brain, red cells, kidneys, colon, many other organs
  GLUT 2 Act as B-cell glucose sensor B cells of islets , liver
  GLUT 3 Basal glucose uptake Brain, placenta, kidneys
  GLUT 4 Insulin-Dependent glucose uptake Skeletal and cardiac muscle, adipose tissue,
  GLUT 5 Fructose transport Jejunum, sperm
  GLUT 6 None Pseudogene
  GLUT 7 Glucose 6-phosphate transporter in endoplasmic reticulum Liver, other tissues

Glucose transporter in myocyte is (AIIMS Nov 09)

a. GLUT1                
b. GLUT2
c. GLUT3                
d. GLUT 4    



Mechanism of secretion

  1. Glucose enters β cells via GLUT 2 transporters, which is metabolized to produce ATP.
  2. Increased ATP inhibits ATP sensitive K+  channels, resulting in ↓ K+ efflux which depolarizes the β cells.
  3. This opens voltage-sensitive Ca2+ channels. The Ca2+ influx causes insulin release by exocytosis.

Description: insulin-secretion-w500









Amino acids (leucine, arginine, others)


Intestinal hormones (GIP, GLP-1, gastrin, secretin, CCK)

α Adrenergic stimulators

β Keto acids

β Adrenergic blockers




Thiazide diuretics

Cyclic AMP and various cyclic AMP-generating substances

K+ depletion

β-Adrenergic stimulators





Microtubule inhibitors

Description: SEC

3. Insulin Receptors:
The insulin receptor is a tetramer made up of two α and two β glycoprotein subunits.

  • The gene for the insulin receptor is located on chromosome 19.
  • The α subunits bind insulin and are extracellular, whereas the β subunits span the membrane.
  • The intracellular portions of the β subunits have tyrosine kinase activity
  • Binding of insulin triggers the tyrosine kinase activity of the β subunits, producing autophosphorylation of the β subunits on tyrosine residues.
  • Insulin receptor substrate (IRS-1) mediates some of the effects in humans but there are other effector systems also

Test Your Skills Now!
Take a Quiz now
Reviewer Name