The pituitary gland produces and secretes growth hormone, which raises blood glucose levels by increasing protein synthesis and promoting the breakdown of fatty acids in adipose tissue. Stress, exercise, a high-protein diet, and hypoglycemia increase its secretion. Growth hormone prevents hypoglycemia by stimulating the release of glycogen from the liver.

Cortisol, produced in the adrenal cortex, maintains normal liver gluconeogenesis and aids in the conversion of amino acids into glucose in the liver. A potent inhibitor of glucose uptake by tissues, cortisol elevates blood glucose levels and resists the action of insulin. Cortisol levels increase in the early morning and in response to stress and hypoglycemia.

• glucagon-secreting alpha cells
• insulin-secreting beta cells
• somatostatin-secreting delta cells.

These islets also contain F cells that secrete pancreatic polypeptide, an exocrine hormone. Unlike exocrine cells, the endocrine cells release their secretions into capillaries rather than into ducts.

Glucagon

Produced and secreted by the alpha cells of the islets of Langerhans, glucagon increases blood glucose levels via a negative feedback system. Glucagon restores normal blood glucose levels by stimulating hepatic glucose production through glycogenolysis (the breakdown of glycogen into glucose by hepatic enzymes), glucagon sustains these blood levels through gluconeogenesis (the formation of glycogen from free fatty acids and proteins). An increase in circulating amino acid levels-which occurs with high-protein meals, exercise, and sympathetic nerve stimulation-stimulates glucagon secretion. Somatostatin and decreased blood glucose levels inhibit glucagon secretion.

Insulin

Normally, the pancreas releases insulin into the bloodstream in small pulsating increments at a rate of 1 to 2 units (U) per hour; after meals, the rate increases to 4 to 6 U per hour . Insulin levels begin to increase 8 to 10 minutes after a person eats and reach their peak in 30 to 45 minutes. Blood glucose levels quickly decline, returning to baseline 1 1/2 to 2 hours after the initial ingestion of food.

The beta cells of the islets of Langerhans increase insulin secretion when blood glucose levels rise, for example, after a person finishes a meal; when blood levels of amino acids, glucagon, and secretin rise and when the parasympathetic nervous system stimulates the beta cells. Insulin lowers blood glucose levels by binding to receptors on the surface of cell membranes and promoting the movement of glucose from the bloodstream into the cells. Insulin also promotes the movement of potassium, phosphate, and magnesium into the cells.

Insulin secretion decreases as blood glucose levels fall between meals and overnight when a person doesn’t eat. As insulin levels fall, glycogen stores in the liver release glucose. When glycogen stores fall, as with continued fasting, muscle cells release amino acids to be converted to glucose. If energy needs remain unmet, adipose tissue releases fatty acids, which are converted into glucose (this conversion is called lipolysis). Fatty acids then are metabolized to form ketones (this process is called ketogenesis).

The hormones glucagon, epinephrine, growth hormone, and cortisol counteract the effects of insulin by promoting the release of glycogen, which raises blood glucose levels. Normally, insulin and the other hormones provide a system of checks and balances that maintains blood glucose levels in the range of 70 to 120 mg/dl.

Somatostatin

Somatostatin, also called the growth hormone­inhibiting hormone, is secreted by the delta cells of the islets of Langerhans. Somatostatin regulates alpha and beta cell function and inhibits the secretion of insulin, glucagon, and pancreatic polypeptide.

Pancreatic polypeptide

Produced by the F cells of the islets of Langer­hans, pancreatic polypeptides inhibit pancreatic bicarbonate and protein secretion. Pancreatic polypeptides also help to relax the gallbladder, releasing bile to aid in digestion. Somatostatin inhibits the secretion of pancreatic polypeptides.

How Pancreas helps

The pancreas helps regulate and maintain homeostasis by performing both exocrine and endocrine functions. As part of the exocrine system, the pancreas aids in the digestion of proteins, fats, and carbohydrates. As part of the endocrine system, the pancreas plays an important role in metabolizing glucose and regulating blood glucose levels. In people with diabetes, a dysfunction in glucose metabolism leads to hyperglycemia.

Location and Structure

The pancreas lies in the upper abdominal cavity behind the stomach and in front of the first and second lumbar vertebrae. It also lies over the inferior vena cava and the two large renal arteries. Measuring 12 to 15 cm in length and weighing about 60 grams, the pancreas is divided into a head, body and tail. The head of the pancreas lies in and is attached to the C-shaped duodenal loop. The body of the pancreas extends horizontally across the upper abdomen and the tail touches the spleen.