Modern pharmacauticals are an area where body chemistry is extremely important and constantly discussed. Body chemistry is defined as the chemical reactions and interactions that occur throughout the human body. There are literally a countless number of interactions that are occuring in the human body at any point in time. Proteins are interacting with other proteins, sugars, nucleic acids, and small molecules to facilitate responses. Enzymes are interacting with sustrates to facilitate chemical reactions. Acids and microbes are interacting with food molecules in the stomach and intestines to faciliate the breakdown of digested food.
In pharmaceuticals, we are concerned with how small molecules interact with specific receptors (often proteins) in the body. Most importantly, we want to maximize the desired chemical interactions while minimizing unwanted or detrimental interactions so as to reduce side effects. Chemists and biologists spend years mapping out and studying body chemistry to try and make a drug work in a clinical setting. Even besides minimizing side effects there are numerous other issues to work out such as making an oral drug that can survive the stomach and digestion process and make it into the bloodstream, a brain drug that can cross the notorious blood-brain barrier, and a drug that won't be cleared through the liver or kidneys before it can have its desired effect.
Understanding body chemistry is extremely important in the field of clinical laboratory science. Say you are not feeling fatigued and go to a doctor. The doctor might decide to draw your blood to run tests for liver, kidney, and thyroid function. The blood is sent to the clinical laboratory where clinical lab scientists (CLS or medical technologists) run biochemical assays to determine levels or activities of specific enzymes.
When an organ is diseased it may release compounds into the blood. An increase (or decrease depending on what is being tested) of a specific compound can signify a diseased state. For example, an increase in the level of the enzyme alanine transaminase (ALT) indicates that the liver is inflamed. ALT is an enzyme that is normally found in liver cells. However, if the liver is damaged (e.g. due to hepatitis or liver inflammation) ALT can be released into the blood stream.
Identifying ways that disease alters body chemistry is important for the development of better diagnostic tools. For certain diseases, like cancer, early detection is important for the best outcome. Understanding exactly what part of the body is dysfunctional is critical for treatment decisions.