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10.2: Main Functions for Homeostasis

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    84056

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    Supplying Nutrients

    The digestive system has six main functions. One function is to supply nutrients needed in several ways by body systems. For example, nutrients are needed for building and maintaining structures such as bones, producing substances such as glandular secretions and neurotransmitters, and supplying energy to power the operations of all body systems. To maintain homeostasis, the nutrient supply must be steady so that the body cells have adequate amounts of each required material at all times while not being exposed to excessive amounts of any nutrient.

    Converting Foods to a Usable Form

    Five processes are involved in supplying nutrients at proper and fairly steady levels. One is converting foods to a usable form. This is necessary because although foods provide most of the nutrients later supplied by the digestive system, they are usually not in a form that can be used by the body. For example, it is impossible to swallow a whole apple, have chunks of meat float through the blood vessels, or have a piece of candy enter a brain cell. To pass through the circulatory system and into cells, foods must be converted into small molecules that are dissolved. The main aspects of this conversion process include mechanically breaking large pieces of food into small pieces by chewing; adding saliva to moisten food and dissolve small molecules; and chemically breaking large nutrient molecules into smaller ones by using enzymes in digestive juices.

    Absorption

    Once nutrients are in a usable form, the digestive system moves them from the GI tract into the circulatory system. This step is called absorption. The blood and lymph distribute the absorbed nutrients to other body regions.

    Manufacturing Certain Materials

    Some nutrients cannot be obtained from foods in adequate amounts. The digestive system compensates for some of these deficiencies by manufacturing certain nutrients. For example, only a portion of the substance called vitamin K, which helps form blood-clotting materials, is obtained from foods. The rest is produced by bacteria in the large intestine. Also, certain types of foods have inadequate amounts of the amino acids needed to repair muscle cells and build red blood cells. The liver can manufacture some of these amino acids so that they are supplied at proper and fairly steady rates even when they are not eaten regularly.

    Storing and Converting Excess Nutrients

    Though certain foods have inadequate amounts of some nutrients, they often have a great abundance of others. Furthermore, people usually eat only occasionally during the day and eat only a few types of food. Therefore, the GI tract periodically absorbs large quantities of certain nutrients. To prevent body cells from receiving excessive amounts of these nutrients and becoming deficient in others, the liver performs the fourth and fifth steps in supplying nutrients: storing excess nutrients until they are needed and converting excess nutrients into other nutrients that are in low supply in the foods eaten.

    Eliminating Toxins and Wastes

    A second main function of the digestive system is eliminating toxins and wastes. Though most materials absorbed by the GI tract are beneficial, some are harmful to body cells (e.g., alcohol, detergents, industrial solvents, inappropriate medications, bacterial wastes). Body cells are protected from exposure to many of these substances because the liver eliminates them. The liver also eliminates toxic substances produced by body cells, such as ammonia and bilirubin. It converts harmful materials such as alcohol and ammonia into useful or harmless substances and secretes others (e.g., bilirubin) into the GI tract in a liquid called bile. Many substances in bile pass through the GI tract and are eliminated during a bowel movement.

    Other Functions

    Various parts of the digestive system have other functions, including helping with voice and speech (mouth region), storing blood (liver), regulating certain components in the blood (liver), and producing hormones (GI tract and pancreas).


    This page titled 10.2: Main Functions for Homeostasis is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Augustine G. DiGiovanna via source content that was edited to the style and standards of the LibreTexts platform.