Insulin and glucagon are hormones secreted by islet cells within the pancreas. They are both secreted in response to blood sugar levels, but in opposite fashion! Insulin is normally secreted by the beta cells (a type of islet cell) of the pancreas.
Keeping this in view, how does insulin control blood sugar levels in the body?
This hormone, insulin, causes the liver to convert more glucose into glycogen (this process is called glycogenesis), and to force about 2/3 of body cells (primarily muscle and fat tissue cells) to take up glucose from the blood through the GLUT4 transporter, thus decreasing blood sugar.
What happens if you take insulin?
Insulin reactions. Hypoglycemia, or blood glucose levels that are too low, can sometimes happen when you take insulin. If you exercise too much or don't eat enough, your glucose level can drop too low and trigger an insulin reaction.
Why would you take insulin?
If your pancreas secretes little or no insulin (type 1 diabetes), or your body doesn't produce enough insulin or has become resistant to insulin's action (type 2 diabetes), the level of glucose in your bloodstream increases because it's unable to enter cells.