Insulin is a hormone with a protein structure. Therefore, it’s both part of the Hormone and the Plasma protein found in the blood plasma.
It’s released by beta cells in the pancreas when Glucose is too high. Its overall job is to lower blood glucose, which it does in a few ways:
- Uptake (main role): it lets Glucose enter muscle and fat cells, by moving glucose transporters to the cell surface. Not all tissues need insulin for this (the brain and liver don’t).
- Storage: it signals Glucose to be stored as Glycogen in the liver and muscles.
- Braking the liver: it tells the liver to stop releasing glucose into the blood.
Its counterpart is Glucagon, which raises blood glucose.