Digestion is the process a body uses to turn food into a usable source of energy. For humans and most mammals, digestion starts in the mouth, where enzymes that aid in digestion are released in saliva and help prepare food for further digestion by the stomach and intestines. Acids in the stomach break down complex carbohydrates, such as starches, and smaller particles are absorbed into the bloodstream. The unabsorbed particles then move to the small intestine, where they are further broken down and either absorbed by the intestinal wall to immediately be used as energy or to be stored as energy reserves (fat). What is left is moved to the large intestine for the final stages of absorption and digestion, and the unusable waste is expelled from the body as excrement.

Maintaining Homeostasis: pH Balance

The process of digestion seems deceptively simple: Matter moves into the body and continues down a conveyer beltlike chain of organs that break it down completely before it leaves the body. Yet the maintenance of such a system is complex and relies on a balance of pH and helpful bacteria to maintain homeostasis. Both acidic and basic pHs are required at various points in digestion to maintain balance during the process. Saliva in the mouth, the starting point of digestion, is only mildly acidic for the purpose of initially breaking down the food without damaging the teeth or delicate throat tissue. The stomach, on the other hand, needs to be highly acidic to jump-start the breakdown process as well as act as a defense for the body against any harmful bacteria or other intruders. To balance things out on the basic side, it is important that the small intestine has a high pH, because most of the enzymes used in digestion can’t function properly in an acidic environment.

Maintaining Homeostasis: Helpful Bacteria

Helpful bacteria also are integral to maintaining homeostasis in the digestive system. It is estimated that the average human has around 500 species of helpful bacteria, also known as intestinal microflora, in his digestive tract, mostly concentrated in the large intestine. These bacteria aid in digestion, help produce vitamins, help formulate excrement and guard against harmful bacteria. When the bacteria population in a digestive tract is thrown off or decimated, the host will notice a change in the pace and quality of digestion. Microflora species have such a positive effect on their host that there are many products available, mostly yogurts, that contain material that supports intestinal microflora's growth and health.