1. Biology 1-2

2. Mouth and Pharynx Digestion begins in the mouth. Teeth tear and shred food. Salivary glands secrete saliva, a mix of amylase (breaks down starch) and water. Partially digested food passes through the pharynx. The pharynx connects the mouth to the esophagus. The epiglottis closes off the larynx, preventing food from entering the lungs.

3. The Esophagus The esophagus connects the pharynx to the stomach. Sits behind the larynx (voice box).

4. The Esophagus cont’d The food is pushed down the esophagus by peristalsis. Peristalsis-rhythmic contractions that move the bolus through the alimentary canal. Caused by contractions of the smooth muscle of the esophagus, stomach, small and large intestines.

5. The Stomach Chemical digestion continues in the stomach. The stomach secretes gastric juice, a mix of: Mucus (protects the stomach) Hydrochloric acid (denatures proteins and kills bacteria) Enzymes to break down proteins.

6. The Small Intestine Food passes from the stomach to the small intestine. Enzymes from the liver and pancreas enter the small intestine to complete digestion.

7. The Small Intestine cont’d The liver makes bile to break down fats. Bile is stored in the gall bladder before entering the intestine. The pancreas makes enzymes for breaking down organic compounds. Enzymes are secreted into the intestine.

8. The Small Intestine cont’d Absorption occurs in the small intestine. The surface of the small intestine has many folds, called villi. Increase surface area for absorption.

9. The Small Intestine cont’d Blood vessels in the middle of each villus carry away absorbed nutrients. Carried first to the liver. Removes excess glucose and stores it as glycogen. The rest are carried away to be used by the rest of the body. To make ATP (cellular respiration) or organic compounds.

10. The Large Intestine The large intestine reclaims water. Food from the small intestine passes through the large intestine and excess water is reabsorbed. Water enters nearby blood vessels by osmosis. What remains is undigested matter, feces. Feces is stored in latter section of the large intestine, called the rectum. Feces passes out of the body through the anus.

11. The Large Intestine cont’d Bacteria (E. coli) break down undigested matter to make energy. Bacteria produce vitamins (some B’s, K, folic acid, biotin), which are absorbed into the bloodstream through the large intestine.