Metabolism

culled from:www.femalefirst.com


What is Metabolism?
Metabolism is a reference to all the chemical reactions that occur within your body. More specifically, your metabolism is the sum of all energy transformations associated with each chemical reaction in your body. This is the reason why metabolism is commonly discussed from a fitness, exercise, and weight loss perspective, because it ultimately represents your body's regulation of energy or, in other words, calories. Keep reading to learn more about metabolism.

Important Concepts Related to Metabolism
To understand how metabolism works, it is first helpful to understand the simple but fundamental concepts listed below:
1.    Your body's energy source is the food you eat. When you eat food, you are consuming energy stored in a chemical form, the amount of which can be measured by the caloric content (read the Calories Explained article) of whatever you are eating.
2.    Energy can neither be created or destroyed, it can only change form. This is the first law of thermodynamics, and it governs your metabolism (along with everything else in the known universe).

3.    With respect to metabolism and the human body, when we say that calories (i.e. energy) are being "burned," it does not mean that the calories are disappearing. We know that calories can't disappear because calories are units of energy and so that would contravene the first law of thermodynamics (see #2 above). Essentially, calorie burn means that calorie energy is being transformed from the chemical form stored within your body to either a heat or mechanical form that is not stored within your body.
4.    All chemical reactions must either release energy or else absorb energy. Each chemical reaction within your body must be accompanied by a release of energy or an absorption of energy.
The Basic Physiology of Metabolism
Now that you understand the fundamental concepts that govern metabolism, we can review the specifics of metabolism. From item #4 on the list above, you know that there are two basic types of chemical reactions, ones that release energy and ones that absorb energy. When discussing metabolism, these types of reactions are classified as catabolic and anabolic reactions, respectively. They are described in more detail below:
Catabolism
Some chemical reactions in our bodies break down nutrient molecules (i.e. molecules from the food we eat) to release useable energy. This is called catabolism. The energy that is released during catabolic reactions is stored within adenosine triphosphate (ATP) molecules. You can learn more about ATP in the