Functions of the Digestive System
The major functions of the digestive tract include the following six processes
1. Ingestion
Food must be placed into the mouth before it can be acted on. This is an active, voluntary process called ingestion.
2. Propulsion
Foods must be propelled from one organ to the next. Swallowing is one example of food movement that depends on peristalsis. Peristalsis is involuntary and involves alternating waves of contraction and relaxation of the muscles in the organ wall. The net effect is to squeeze the food along the tract. Although segmentation may help to propel foodstuffs through the small intestine, it normally only moves food back and forth across the internal wall of the organ, serving to mix it with the digestive juices. Thus, segmentation is more an example of mechanical digestion than of propulsion.
3. Food breakdown: mechanical digestion
Mixing of food in the mouth by the tongue, churning of food in the stomach, and segmentation in the small intestine are all examples of processes contributing to mechanical digestion. Mechanical digestion prepares food for further degradation by enzymes.
4. Food breakdown: chemical digestion
The sequence of steps in which large food molecules are broken down to their building blocks by enzymes.
5. Absorption
Transport of digested end products from the lumen of the GI tract to the blood or lymph is absorption. For absorption to occur, the digested foods must first enter the mucosal cells by active or passive transport processes. The small intestine is the major absorptive site.
6. Defecation
Defecation is the elimination of indigestible residues from the GI tract via the anus in the form of feces.
Some of these processes are the job of a single organ. For example, only the mouth ingests, and only the large intestine defecates.
Activities Occurring in the Mouth, Pharynx, and Esophagus
Food Ingestion and Breakdown
Food Propulsion—Swallowing and Peristalsis
Activities of the Stomach
Food Breakdown
Food Propulsion
Activities of the Small Intestine
Food Breakdown and Absorption
Food Propulsion