University of California
Type of paper: Thesis/Dissertation Chapter
The Function and Mechanics of the Digestive System
In this paper I will explain the function and mechanics of the digestive system. The body’s method of taking the food we eat and breaking it down to obtain vital nutrients that will allow us to live and be healthy is digestion. According to “Wikipedia. com” (2013), “Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones, it is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream” (Digestion). Digestion time varies between individuals and between men and women.
After you eat, it takes about six to eight hours for food to pass through your stomach and small intestine. Food then enters your large intestine (colon) for further digestion, absorption of water and, finally, elimination of undigested food (Picco, M. D. , 2012). The point when food enters the mouth, digestion of the food starts by the action of mastication, a form of mechanical digestion where the teeth allow the chewing of food to aid in the digestive process and the wetting contact of saliva (“Wikipedia. com”, 2013).
Saliva, a liquid secreted by the salivary glands, contains salivary amylase, an enzyme which starts the digestion of starch in the food. After undergoing mastication and starch digestion, the food will be in the form of a small, round slurry mass called a bolus. It will then travel down the esophagus, the portion of gastrointestinal tract that reaches from the pharynx, and into the stomach, the organ in the digestive tract that mixes food and secretes gastric juice, by the action of peristalsis, this process can be 2 to 6 hours.
Gastric juice in the stomach starts protein digestion. Gastric juice mainly contains hydrochloric acid and pepsin. As these two chemicals may damage the stomach wall, mucus is secreted by the stomach, providing a slimy layer that acts as a shield against the damaging effects of the chemicals. While protein digestion is occurring, mechanical mixing occurs by peristalsis, waves of muscular contractions that move along the stomach wall. This allows the mass of food to further mix with the digestive nzymes, typically an hour or two in humans (“Wikipedia. com”, 2013). The resulting thick liquid is called chyme.
When the pyloric sphincter valve opens, chyme enters the duodenum where it mixes with digestive enzymes from the pancreas, and then passes through the small intestine,a tube shaped organ of the digestive tract where digestion of ingested food is completed and the majority of nutrient absorption occurs and digestion continues from 3 to 5 hours. When the chyme is fully digested, it is absorbed into the blood. 5% of absorption of nutrients occurs in the small intestine.
Water and minerals are reabsorbed back into the blood in the colon (large intestine) where the pH is slightly acidic about 5. 6 ~ 6. 9. Some vitamins, such as biotin and vitamin K (K2MK7) produced by bacteria in the colon are also absorbed into the blood in the colon (“Wikipedia. com”, 2013). This process could take up to 24 hours. Waste material is eliminated from the rectum during defecation through the anus, the lower opening of the digestive tract through which the feces leave the body.