Content Reviewers:Yifan Xiao, MD
Contributors:Sam Gillespie, BSc
These cells are found within clusters of endocrine cells called the islets of Langerhans, which are distributed across the pancreas.
Insulin’s main function is to facilitate the transport of glucose from the blood into the various insulin-responsive tissues like muscle cells and adipose tissue. This hormone binds to insulin receptors on the surface of the cell membrane.
Now, these receptors have two alpha and two beta subunits. Alpha subunits are located outside of the cell and they bind insulin; while two beta subunits are located within the cell and they have tyrosine kinase activity which carries signals into the cell.
Next, the GLUT4 proteins embed themselves into the membrane and allow glucose to move into the cell.
Finally, insulin activates Na+/K+- ATPase pumps and shifts potassium into intracellular space, thereby decreasing potassium levels in the blood.
When injected into the abdominal region, the absorption is the quickest, followed by arms, thighs, and buttocks.
Some diabetics prefer the insulin pump since insulin dosages are programmed into the device and will be delivered subcutaneously throughout the day, thus preventing the need for multiple daily insulin injections.
These preparations are categorized according to their onset of action and duration of effect; and they include rapid-acting, short-acting, intermediate-acting, long-acting, and ultra long-acting insulins.
Intermediate-acting, long-acting, and ultra long-lasting insulins are used for basal insulin regimen to maintain a steady background level of insulin throughout the day.
They are given once or twice daily to regulate the basal, or fasting blood glucose, level.
Lastly, is the sliding-scale regimen. This regimen is typically reserved for hospital settings where a person’s blood glucose level could fluctuate rapidly due to metabolic stressors like infections or other illnesses.
This makes them less stable, and they break down into single monomers soon after injection.
Rapid-acting insulins begin working within 5 to 15 minutes of administration, with a peak effect at 1 hour. Their effects last for 3 to 4 hours.
Thus, regular insulin only begins working 30 minutes after administration and its effect peaks at 2-3 hours.
- "Katzung & Trevor's Pharmacology Examination and Board Review,12th Edition" McGraw-Hill Education / Medical (2018)
- "Rang and Dale's Pharmacology" Elsevier (2019)
- "Goodman and Gilman's The Pharmacological Basis of Therapeutics, 13th Edition" McGraw-Hill Education / Medical (2017)
- "Insulin lispro: a fast-acting insulin analog" Am Fam Physician (1998)
- "Rapid-Acting and Human Insulins: Hexamer Dissociation Kinetics upon Dilution of the Pharmaceutical Formulation" Pharmaceutical Research (2017)
- "Short-acting insulin analogues versus regular human insulin for adults with type 1 diabetes mellitus" Cochrane Database of Systematic Reviews (2016)