What Does the Term Metabolism Mean?

What Does the Term Metabolism Mean?
Each and every second of every day our cells are engaged in the oper-
ations 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 reac-
tions 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 tem-
perature 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.




Table  Primary Functions of the Major Tissue and Organs in Our Body
Bone              Provides structure and the basis of movement of limbs and
                  our entire body. Also serves as a mineral storage. Primarily
                  composed of minerals and protein and smaller amount of
                  cells, nerves and blood vessels.
Skeletal muscle   We have three kinds of muscle (skeletal, cardiac (heart) and
                  smooth), which is largely water and protein and to a lesser
                  degree carbohydrate and fat. Contraction of muscle results in
                  movement of some type. Skeletal muscle is connected to bone
                  and provides movement of our limbs and body.
Heart and blood   Our heart is mostly muscle (cardiac). Contraction of cardiac
                  muscle establishes the blood pressure in our heart, which
                  drives blood through our blood vessels. We have about
                  100,000 miles of blood vessels and our blood is, for the most
                  part, a delivery medium!
Smooth muscle     Smooth muscle lines tubes in our body such as airways, blood
                  vessels, digestive tract, reproductive tract, etc.) Smooth
                  muscle is responsible for regulating the flow of content (gases,
                  fluids, semi-solids) through those tubes.
Lungs             Serves as the site of oxygen and carbon dioxide exchange
                  between our body and the air around us.
Liver             Perhaps the "hub" of nutrition. Our liver is involved in
                  maintain blood glucose, regulating blood lipid levels,
                  processing amino acids, making plasma proteins (e.g., clotting
                  factors, transport proteins), and bile and metabolizing and
                  storing many vitamins, minerals, and other nutrients.
Kidneys           Regulate the composition of our body fluid. They do this by
                  filtering and regulating the composition of our blood, which
                  in turn regulates the composition of the fluid in-between our
                  cells and inside of our cells.
Adrenal glands    Our adrenals are steroid hormone producing factories. They
                  produce cortisol (stress hormone), aldosterone, a lot of
                  DHEA and lesser amount of androstenedione, testosterone,
                  and estrogens.
Thyroid gland     Produces the hormones thyroid hormone and calcitonin.
                  Thyroid hormone is one of the most influential hormones in
                  regulating our energy expenditure.
Brain and spinal  Our brain is an information processing center and the spinal
cord              cord is the conduit for signals to leave (or be carried to) our
                  brain to the rest of our body. Our brain initiates and regulates
                  muscle activity, processes sensory information and controls
                  body temperature and appetite.
Skin              Site of heat removal and protective coating. Some vitamin D is
                  produced in our skin.
Pancreas          Produces the hormones insulin and glucagon and digestive
                  enzymes.
Pituitary gland   Produces a slew of hormones including thyroid stimulating
                  hormone (TSH) and adrenocorticotrophic hormone (ACTH).