Mechanical vs. Chemical Digestion Mechanical digestion is physically smashing large chunks of food into smaller chunks of food. Chemical digestion uses chemicals (enzymes) to change the food into different chemicals. (Starch into sugar, for example.) Analogy: –Mechanical digestion is like using a chainsaw to make firewood. –Chemical digestion is like burning the firewood
About Enzymes Enzymes are special protein molecules produced by the body. They make chemical reactions in the body happen faster (make food break down much faster than it would otherwise). They are not used up in these reactions - they can be used over and over again.
Chemicals in the Digestive System Mouth: Amylase - enzyme in saliva that begins to break down starch into sugar.
Stomach: Pepsin - enzyme in gastric juices (stomach juices) that begins digesting protein. Hydrochloric acid - allows pepsin to work more quickly –Common stomach problems: –Heartburn - stomach acid gets up into the esophagus –Ulcer - stomach juices begin to digest the wall of the the stomach - mucus normally helps protect stomach lining
Small intestine Most of our food is digested in the first 25 cm or so called the duodenum. –Intestinal juice –produced by cells in the wall of the small intestine contains enzymes that digest carbs, fats, proteins. –Pancreatic juice –produced by the pancreas and squirted into the small intestine contains enzymes that digest carbs, fast, proteins –Bile –produced by the liver and stored in the gall bladder until needed. NOT an enzyme! It DOES NOT chemically change food - it mechanically breaks up big globs of fat into smaller globs so the enzymes can work on it easier.
Absorption Absorption of most nutrients (carbs, fats, proteins, some vitamins and minerals) happens in the lower portion of the small intestine called the ileum. Food nutrients diffuse through the wall of the small intestine into the bloodstream. Nutrients must be dissolved in water for this to take place.
Villi –Villi - small, finger-like projections that line the surface of the ileum. Give a velvety appearance - shag carpet –Villi contain blood vessels and lymph vessels –Blood carries sugars, amino acids, minerals, some vitamins Lymph carries fatty acids and some vitamins. The folds of the villi greatly increase the surface area of the small intestine, giving more opportunities for nutrients to be absorbed.
Large Intestine –The large intestine (colon) removes excess water from the undigested materials and returns it to the body. –Diarrhea - not enough water is absorbed by the large intestine. Constipation - too much water is removed or not enough fiber in the person’s diet. Some bacteria in the colon feed on cellulose (fiber) and produce vitamins the body needs.
Anus Opening below the rectum through which solid waste exits the body