Pancreatic (alpha/beta) cells synthesize and secrete insulin.
Content Reviewers:Rishi Desai, MD, MPH
Insulin is a type of peptide hormone that reduces the amount of glucose in the blood.
It is produced in the pancreas by beta cells.
These cells are found within clusters of endocrine cells called the islets of Langerhans, which are distributed across the pancreas.
If the body is unable to produce enough insulin, then insulin therapy is used to keep the blood glucose low.
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.
Glycogenesis is the process that takes place in the liver and skeletal muscles.
Finally, insulin activates Na+/K+- ATPase pumps and shifts potassium into intracellular space, thereby decreasing potassium levels in the blood.
Finally, insulin inhibits lipolysis, the breakdown of lipids; and proteolysis, the breakdown of proteins.
The result is the destruction of the beta cells which leads to decreased insulin production and hyperglycemia, or increased blood glucose.
Type 2 diabetes is caused by insulin resistance in the cells of the body.
When blood glucose rises after a meal, the pancreas produces insulin as a response.
Eventually, the poor pancreas gets so overworked that the beta cell starts to atrophy, which leads to decreased insulin production and high blood glucose levels.
Insulin is administered subcutaneously because they can be broken down in the GI tract.
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.
Rapid-acting and short-acting insulins are used for bolus insulin regimen, where they are taken before each meal to counteract the post-meal increase in blood glucose.
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.
Next, there’s basal-bolus regimen where a basal insulin is used to maintain fasting blood glucose levels, and a bolus insulin is taken before meals.
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.
In this regimen, every 4-6 hours, the person’s glucose level is measured and an appropriate dosage of short acting insulin is given.
Now let’s look at each class of insulin, starting with rapid-acting insulins, which include insulin aspart, lispro, and glulisine.
These medications are given subcutaneously and they are actually modified versions of regular insulin with different sequences of amino acids.
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.
These insulins are injected right before a meal or they can be used in insulin pumps.
This structure allows insulin to remain stable within the body, and break down into individual monomers in order to become active.
Thus, regular insulin only begins working 30 minutes after administration and its effect peaks at 2-3 hours.
Next up is the intermediate-acting insulin known as NPH insulin, which stands for neutral protamine hagedorn.
It’s created through the addition of protamine and zinc to regular insulin.
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