A healthy gastrointestinal tract is important in maintaining the overall health of the body. Understanding the complex digestion process is important to understanding how maintaining a healthy GI tract contributes to promoting a healthy immune system, and maintaining the overall health of the body. Digestion is the metabolic process that converts foodstuffs within the body for use. The process begins in the mouth, where it is chewed and mixed with saliva to prepare it for swallowing. After swallowing, the food is pushed through the esophagus, which transports it to the stomach, where it is further diluted and mixed with enzymes, breaking down the food to be absorbed in the intestines. Most of the absorption process begins to take place in the small intestine. Macronutrients, minerals, vitamins, trace elements and water are absorbed here before reaching the colon. The nutrients pass through the small intestine's wall, which contains small, finger-like structures called villi.
The blood, which contains the absorbed nutrients, is carried away from the small intestine and goes to the liver for filtration, toxin removal and nutrient processing. The primary function here is regulation of blood glucose levels through a process of temporary storage of excess glucose that is converted in the liver to glycogen in response to insulin. The colon is the final step in the digestion process. The remaining water is reabsorbed in the colon as well as any substance that cannot pass through the villi such as dietary fiber. Digestion is a complex process, which is controlled by several factors. The gastrointestinal tract is also a prominent part of the immune system. The low pH (ranging from 1 to 4) of the stomach is fatal for many microorganisms that enter it. Similarly, mucus neutralizes many of these microorganisms. Other factors in the GI tract help with immune function as well, including enzymes in the saliva and bile.