What Does the Term Metabolism Mean?

Each and every second of every day our cells are engaged in the operations that help keep them alive and well. At the same time the efforts of each cell also contribute to the proper functioning of our body as a whole. To do so each cell must perform an incredible number of chemical reactions every second. The term metabolism refers to those chemical reactions collectively.
 

The term metabolism is somewhat general. For instance, total body metabolism refers to all the energy released from all the chemical reactions and associated processes in our body. Said differently, total body metabolism is the total of all reactions taking place in each cell added together. However, if we wanted to describe just those chemical reactions within a specific tissue, such as muscle or bone, we would say “muscle
metabolism” or “bone metabolism.” We can be even more focused and use the term metabolism to describe only those reactions associated with a single nutrient or nutrient class. For example, if we were discussing the

chemical reactions that involve only proteins or carbohydrates, we would be discussing protein or carbohydrate metabolism, respectively.
 

In general, chemical reactions and/or pathways will release energy. Ultimately, this extra energy will be converted to heat. Since body temperature remains fairly constant, the heat produced in metabolism must be removed from our body. Therefore, our total body metabolism can be estimated by measuring how much heat is lost from our body. Researchers can do this in specialized laboratories as discussed in a later chapter.