Insulin
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Insulin
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Aspart insulin
β2 -agonists
insulin and p. 331
C-peptide
insulin and p. 331
in insulinomas p. 357
Detemir insulin
Glargine insulin
Glucagon p. 333
insulin and p. 331, 333
Gluconeogenesis p. 76
in insulin deficiency p. 350
Glucose
insulin and p. 333
Glulisine insulin
Glycogen p. 84
insulin and p. 331
Glycogenolysis
in insulin deficiency p. 350
Insulin p. 333
anabolic effects of p. 331
deficiency in p. 350
diabetic ketoacidosis p. 355
for HHNS p. 355
fructose bisphosphatase-2 and p. 74
GIP effect on p. 378
glucagon and p. 333
glycogen regulation p. 71, 84
hypokalemia from p. 608
in pregnancy p. 331
production of p. 337
secretion of p. 333
signaling pathways for p. 351
somatostatin and p. 378
somatostatinomas and p. 355
Insulinomas
insulin and C-peptide in p. 331
Insulin preparations p. 358
Ketogenesis
insulin deficiency p. 350
Lipolysis
insulin and p. 333
in insulin deficiency p. 350
Lispro insulin
Osmotic diuresis
insulin deficiency/insensitivity p. 350
Plasma osmolality
insulin deficiency/insensitivity p. 350
Pregnancy p. 651
insulin in p. 331
Protein synthesis p. 184, 196
insulin and p. 333
Proteolysis
in insulin deficiency p. 350
Regular insulin
Sulfonylureas p. 359
insulin and p. 331
Triglycerides
insulin and p. 331
Tyrosine kinase
insulin and p. 331
Transcript
Insulin is a hormone that’s involved in lowering the blood sugar levels or glycemia after a meal. Insulin comes from the latin insula, which means island, because this hormone is produced by some small islands of cells scattered throughout the pancreas that are called pancreatic islets or islets of Langerhans.
The pancreas lies in the upper left part of the abdomen, right behind the stomach. The vast majority of the pancreas is made up by exocrine glands in charge of secreting digestive enzymes into the small intestine to help digestion. But about 1 to 2% of the mass of the pancreas is made up by the islets of Langerhans, which are endocrine glands made up by five different cell types, and each cell type secretes a specific hormone. The most abundant are the beta cells, which produce insulin. But you can also find alpha cells that secrete glucagon, delta cells that secrete somatostatin, gamma cells that secrete pancreatic polypeptide, and finally epsilon cells that secrete ghrelin.
Let’s focus on beta cells. Beta cells are in charge of producing insulin, which is a peptide hormone encoded by the INS gene on chromosome 11. Insulin is first synthesized as a single polypeptide called preproinsulin. A short tail called leader or signal peptide is cleaved from preproinsulin to form proinsulin. Proinsulin consists of three peptide chains in the order B, C for connecting peptide, and A. Proinsulin is then further cleaved at two positions, releasing a fragment called the C-peptide, and leaving the B- and A- chains, and two disulfide bonds which link the B- and A- chains together to form insulin. This mature insulin is stored inside granules within the beta cells where it waits until it’s released into the blood.
The most important trigger for insulin secretion is glucose. Beta cells are sensitive to glucose concentrations in blood, and when blood glucose levels rise, beta cells secrete insulin into the blood to help lower those levels and store glucose. Other stimulatory factors for insulin secretion include hormones like glucagon and cortisol, which stimulate insulin indirectly by increasing blood glucose levels, increased fatty acid or amino acid concentrations in blood, since insulin is also involved in their storage, and acetylcholine from the parasympathetic nervous system, which helps with digestion, and stimulates insulin secretion to decrease the recently absorbed glucose in blood.
Summary
Insulin is a hormone that helps the body to metabolize sugar (glucose). It is made by the pancreas, specifically the islets of Langerhans.
Insulin controls how much glucose is in the blood. When you eat, your body breaks down food into glucose and other nutrients. These enter the bloodstream and signal the pancreas to make insulin. The insulin then allows the glucose to enter cells in the body, where it is used for energy or stored for later use.
Sources
- "Medical Physiology" Elsevier (2016)
- "Physiology" Elsevier (2017)
- "Human Anatomy & Physiology" Pearson (2018)
- "Principles of Anatomy and Physiology" Wiley (2014)
- "Insulin: understanding its action in health and disease" British Journal of Anaesthesia (2000)
- "Are islet cells the gatekeepers of the pancreas?" Pancreatology (2002)
- "A Reappraisal of the Blood Glucose Homeostat which Comprehensively Explains the Type 2 Diabetes Mellitus–Syndrome X Complex" The Journal of Physiology (2003)