Insulin is a key hormone regulating glucose homeostasis. Its major target tissues are the liver, the skeletal muscle and the adipose tissue. At the cellular level, insulin activates glucose and amino acids transport, lipid and glycogen metabolism, protein synthesis, and transcription of specific genes.

Insulin levels are regulated by the balance of insulin production by the pancreas and its subsequent clearance and insulin sensitivity within maternal muscle, liver, and fat tissues.

However, insulin action directly on vascular endothelium, atherosclerotic plaque macrophages, and in the heart, kidney, and retina has now been described, and impaired insulin signaling in these locations can alter progression of cardiovascular disease in the metabolic syndrome and affect development of microvascular …

The primary targets for insulin are liver, skeletal muscle, and fat. Insulin has multiple actions in each of these tissues, the net result of which is fuel storage (glycogen or fat).

Diabetes is a serious disease that can affect your eyes, heart, nerves, feet and kidneys. Understanding how diabetes affects your body is important.

Physiological Actions of Glucagon at Target Tissues Glucagon exerts its physiological action on target tissues via the G-protein coupled glucagon receptor, which is found on multiple tissues including the liver, fat, intestine, kidney and brain (50,68).

When blood sugar is too high, the pancreas secretes more insulin. When blood sugar levels drop, the pancreas releases glucagon to raise them. This balance helps provide sufficient energy to the cells while preventing the nerve damage that can result from consistently high levels of blood sugar.

Glucagon works along with the hormone insulin to control blood sugar levels and keep them within set levels. Glucagon is released to stop blood sugar levels dropping too low (hypoglycaemia), while insulin is released to stop blood sugar levels rising too high (hyperglycaemia).

The α-cell of the pancreatic islet modulates glucose homeostasis by secreting glucagon that acts primarily by driving hepatic glucose production. Glucose sensing of the α-cell becomes defective in both type 1 and type 2 diabetes, resulting in hyperglucagonemia that likely contributes to hyperglycemia (1).

Epinephrine directly stimulates glucagon secretion in normal human subjects, and stimulation of the autonomic sympathetic nervous system innervation to the pancreas elicits an increase in α cell secretion.

The two most abundant and prominent endocrine cell types, the beta and the alpha cells, are essential for the maintenance of blood glucose homeostasis. While the beta cell produces insulin, the only blood glucose-lowering hormone of the body, the alpha cell releases glucagon, which elevates blood glucose.

Glucagon is a 29-amino acid peptide hormone, the main secretory product of the pancreatic alpha-cells, acting to increase plasma glucose levels.

Insulin stimulates the liver to store glucose in the form of glycogen. A large fraction of glucose absorbed from the small intestine is immediately taken up by hepatocytes, which convert it into the storage polymer glycogen. Insulin has several effects in liver which stimulate glycogen synthesis.

Individuals affected by excess weight, particularly obesity and morbid obesity, are more likely to develop type 2 diabetes as a related condition of their excess weight.

pancreas

The normal human pancreas contains about 1 million islets. The islets consist of four distinct cell types, of which three (alpha, beta, and delta cells) produce important hormones; the fourth component (C cells) has no known function.

The feedback system of the pancreatic islets is paracrine—it is based on the activation and inhibition of the islet cells by the endocrine hormones produced in the islets. Insulin activates beta cells and inhibits alpha cells, while glucagon activates alpha cells, which activates beta cells and delta cells.

α-Melanocyte–stimulating hormone (α-MSH) is secreted into the systemic circulation from the intermediate lobe of the pituitary; it and related melanocortin peptides, derived from the precursor proopiomelanocortin (POMC), are also expressed in numerous CNS and peripheral structures.

Glucagon, a hormone secreted from the alpha-cells of the endocrine pancreas, is critical for blood glucose homeostasis. It is the major counterpart to insulin and is released during hypoglycemia to induce hepatic glucose output.

Pancreatic glucagon, the hyperglycemic hormone secreted by the alpha cells of the islets of Langerhans, promotes glycogenolysis, neoglucogenesis, lipolysis, and ketogenesis.