Functions of Gastrointestinal System
The gastrointestinal system is the portal through which all nutrients, such as carbohydrates, fats, proteins, vitamins, minerals, and water, required by the body enter. Before the nutrients enter the body, they need to be processed in many ways. Food must be broken down into smaller particles. Once broken into smaller pieces, the different components of food must be reduced to a chemical form that can be ab-sorbed by the epithelium of the gut. The remaining waste material must then be eliminated from the body. For this to occur, many specific processes are involved.
The food must be ingested—taken in via the mouth. This involves conscious choice; areas in the brain regulate the quantity and type of food that is in-gested. Once ingested, the food is mechanically processed. This includes breaking the food into smaller pieces and changing the consistency to allow it to be easily swallowed. The mechanically processed food is then ready for digestion. Digestion refers to breaking the food down into small organic pieces us-ing enzymes, assuring that the food particles are small enough to be absorbed by the epithelium cov-ering the gut. Many enzymes manufactured in vari-ous parts of the digestive system help with that process.
The enzymes, together with water, acids, elec-trolytes, and salts, are secreted into the gut to help with digestion. The digested food is then absorbed by the epithelium lining the gut and passed into the cir-culation and the lymphatics. This material, some of which is processed in the liver, enters the general cir-culation and is transported to the various tissue of the body, according to their needs. The remaining food—the waste matter—is excreted from the body by a process called defecation. Specialized innerva-tion of the gut helps move the food from the mouth to the anus.
Exposed to the external environment, the digestive system has its own mechanism for protecting the body from bacteria or toxic materials entering the body.