Insulin plays a central role in the regulation of human metabolism.The key functions of insulin are (a) stimulation of glucose uptake from circulation (b) suppression of hapatic gluconeogenesis.Together regulating glucose homeostasis.
Diabetes is characterised by lack ,or relative deficiency of insulin,lack of sensitivity to endogenous insulin resulting in hyperglycaemia.Long term exposure of tissues to elevated glucose concentration is associated with development of complications e.g..CHD,CVD,,retinopathy,nephropathy and neuropathy.
Once insulin is produced by beta cells of Pancreas in response to glucose,it activates specific cellular receptors called Insulin Rceptors.These receptors modulates multiple post receptor signalling pathways.Insulin thus regulates a host of other cellular processes such as (a) Protein and Fat synthesis, (b) DNA and RNA synthesis (c) Cell growth and differentiation. It how ever the uptake of glucose is of primary concern in the in the manifestation of diabetes.
The insulin receptors take up glucose from blood and transport it to cell membrane.Now specific membrane transporters facilitate the movement of glucose INTO the cell to reduce plasma glucose .The transported glucose is used as metabolic fuel or stored as glycogen.
Now there are two major types of glucose transporters (a) Na+ dependent (b) Na+ independent. Of these two only Na+ independent is Insulin RESPONSIVE.
The presence of active transporters in cell membrane favours movement of glucose into the cells,there by lowering the blood glucose.INSULIN enhances glucose uptake by increasing the number of transporters in plasma membrane of target cells.
High ambient glucose concentration in the islets of Langerhans of Pancreas promote insulin biosynthesis and is primary regulator of secretion.
Degradation of insulin --Insulin has short half life in circulation following release estimated at 4-6 minutes.Circulating insulin is cleared by liver as it passés portal circulation,Kidney is largely responsible for insulin clearance in systemic circulation.
NOTE--Several details including details about transporters have been omitted .
