Insulin

Insulin is a peptide hormone produced by beta cells of the pancreatic islets (also known as islets of Langerhans). It is central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle, and as triglycerides in fat tissue.

Function:

The primary function of insulin is to decrease blood glucose levels. It achieves this by:

• Facilitating glucose uptake: Insulin binds to insulin receptors on cells, triggering a signaling cascade that results in the translocation of GLUT4 glucose transporters to the cell membrane. This allows glucose to enter the cell.
• Stimulating glycogenesis: Insulin promotes the conversion of glucose to glycogen in the liver and muscles for storage.
• Inhibiting glycogenolysis: Insulin suppresses the breakdown of glycogen into glucose.
• Inhibiting gluconeogenesis: Insulin reduces the production of glucose from non-carbohydrate sources in the liver.
• Promoting lipogenesis: Insulin encourages the synthesis of fatty acids and triglycerides in fat tissue.
• Inhibiting lipolysis: Insulin reduces the breakdown of triglycerides into fatty acids and glycerol.
• Promoting protein synthesis: Insulin facilitates the uptake of amino acids and stimulates protein synthesis.

Regulation:

Insulin secretion is primarily stimulated by elevated blood glucose levels. Other factors that can stimulate insulin secretion include:

• Amino acids
• Gastrointestinal hormones (e.g., glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP))
• Parasympathetic nervous system activity

Factors that can inhibit insulin secretion include:

• Low blood glucose levels
• Somatostatin
• Sympathetic nervous system activity

Clinical Significance:

Insulin deficiency or insulin resistance can lead to diabetes mellitus.

• Type 1 diabetes: An autoimmune disease in which the body's immune system destroys the beta cells of the pancreas, resulting in an absolute insulin deficiency. Treatment requires lifelong insulin injections or infusions.
• Type 2 diabetes: A condition characterized by insulin resistance, where cells become less responsive to insulin. The pancreas may initially compensate by producing more insulin, but eventually, it may become exhausted, leading to relative insulin deficiency. Management typically involves lifestyle modifications (diet and exercise), oral medications, and sometimes insulin therapy.

Insulin Preparations:

Various types of insulin preparations are available, differing in their onset of action, peak effect, and duration of action. These include:

• Rapid-acting insulin
• Short-acting insulin
• Intermediate-acting insulin
• Long-acting insulin
• Premixed insulin

The choice of insulin preparation and dosage is individualized based on the patient's needs and is determined by a healthcare professional.