Abstract

Arpan Chanda*, Arunava Chandra Chandra, Dr. Dhrubo Jyoti Sen and Dr. Dhananjoy Saha

ABSTRACT

Insulin which is a peptide hormone is produced by ??cells of the pancreatic islets and it is considered to be the main anabolic hormone of the body. It further regulates the metabolism of carbohydrates, fats and protein by promoting the absorption of glucose from the blood into liver, fat and skeletal muscle cells. In these tissues the absorbed glucose from the blood is thus converted into either glycogen via glycogenesis or fats (triglycerides) via lipogenesis, or, in the case of the liver both glycogenesis and lipogenesis. Glucose production and secretion by the liver is strongly supported by high concentrations of insulin in the blood. Circulating insulin on the other hand also affects the synthesis of proteins in a wide variety of tissues. It is thus an anabolic hormone which promotes the conversion of small molecules in the circulating blood into large molecules inside the cells. Conversely low insulin levels in the blood have the opposite effect that promotes widespread catabolism, especially of reserve body fat. ??cells of the pancreatic islets are specifically sensitive to blood sugar levels thus they secrete insulin into the circulating blood in response to high level of glucose; and conversely inhibits the secretion of insulin when blood glucose levels are low. Insulin is responsible for glucose uptake and metabolism in the cells, therefore reducing the blood sugar level. The ?? cells which are present near the ??cells of the pancreatic islets, takes their cues from the ??cells and secretes glucagon into the blood in just the opposite manner i.e. increased glucagon secretion when blood glucose is low, and decreased glucagon secretion when glucose concentrations are high. Glucagon thus increases blood glucose level by stimulating glycogenolysis and gluconeogenesis in the liver. The secretion of insulin and glucagon into the circulating blood in respective response to the glucose concentrations in the blood is termed as glucose homeostasis. Insulin was the first peptide hormone discovered. Frederick Banting and Charles Herbert Best, working in the laboratory of J.J.R. Macleod at the University of Toronto, were the first to isolate insulin from dog pancreas in 1921. Frederick Sanger sequenced the amino acid structure in 1951, which made insulin the first protein to be fully sequenced. The crystal structure of insulin in the solid state was determined by Dorothy Hodgkin in 1969. Insulin is also the first protein to be chemically synthesized and produced by DNA recombinant technology. It is on the WHO Model List of Essential Medicines, the most important medications needed in a basic health system.