In part one of my discussion about metabolism I discussed the different fuel sources. In part two, I will discuss metabolic regulation, starting with hormones. Hormones are biological compounds made in one part of a body to control another part of the body. The two main hormones that regulate metabolism are insulin and glucagon.
Insulin is secreted from the pancreas and signals muscle cells and fat cells to get their energy from blood glucose. Insulin also signals fat cells to convert excess blood sugar into fat and muscle cells to store excess blood glucose as glycogen (Don't know what glycogen is? Don't worry, glycogen will be discussed later).
Glucagon, which is also secreted from the pancreas, signals actions that oppose insulin. Glucagon inhibits fat and glycogen production. Glucagon signals muscle cells and fat cells to get their energy from stored fat. Thus, glucagon promotes fat breakdown (lipolysis).
There are other hormones that regulate metabolism. They all work similarly to glucagon and oppose the actions of insulin. However, I will not be discussing them here because they go beyond the scope of my talk about metabolism.
Insulin AND glucagon are ALWAYS present in your blood (assuming you're health, i.e. not a Type 1 diabetic). Their effect on your metabolism are dependent on their relative ratio. If you have more insulin than glucagon in your blood, then your body is probably making fat. If you have less insulin than glucagon in your blood, then your body is probably burning fat.
As you can imagine, immediately after a meal, your pancreas secretes more insulin. Your body wants to get its energy from the recently consumed sugars instead of its own energy stores (your fat). However, when you haven't eaten for a while, your pancreas secretes glucagon. This is because it wants your muscle and fat cells to get their energy from your fat stores, not your blood sugar. I'll discuss why in my next post.