The Digestive System Digestion is the process of converting food substances to a state in which they can be absorbed by the lining of the digestive tract. digestive tract = tube, stretched out would be 6.5 to 9 m in adults

A. mouth B. tongue C. pancreas D. liver E. gall bladder F. duodenum G. colon H. ileum I. pharynx J. esophagus K. stomach L. jejunum M. rectum N.anus

B] Steps in Digestion 1. Mechanical digestion: chewing, muscular movements, emulsification a) peristalsis - wave-like motion caused by the contraction of two muscle layers, pushes food forward b) sphincters - rings of muscles that mark the beginning and end of the stomach and other specialized regions, help control the forward movement of food and prevent backflow

2. Chemical digestion: breakdown of foods by enzymes (produced by glands)

3. Absorption: end-products of digestion are absorbed into the bloodstream

4. Egestion: elimination of unabsorbed waste materials

C] Physical and Chemical Digestion 1. Mouth a) physical digestion incisors - cutting food canines - tearing and ripping food pre-molars – crushing food molars - grinding food tongue - moves food around

b) chemical digestion saliva - moistens food, enzyme (amylase) begins to break down starch (polysaccharides)

a) physical digestion 2. Stomach (muscular, stretchable sac) storage and mixing of food

b) chemical digestion 2 L of gastric fluids are secreted by lining per day HCl breaks down fibrous tissue and kills bacteria mucus protects lining from acidity pepsin (enzyme) begins protein digestion

3. Small Intestine a) physical digestion bile produced in the liver emulsifies fats bile is stored in the gallbladder and enters the duodenum

b) chemical digestion c) absorption secretions of sodium bicarbonate from the pancreas neutralize acidic chyme enzymes from pancreas breakdown carbohydrates, fats, proteins enzymes are also made in the duodenum villi - finger-like projections that increase surface area for absorption (in jejunum and ileum)

4. Large Intestine (Colon) concentrates material by absorbing water bacteria produce vitamin K which is absorbed by human body the rectum is the end of the colon and it stores feces (mixture of undigested and unabsorbed material, water, dead bacteria)