1. Your Digestive System The main role of the digestive system is to break down and absorb nutrients that are necessary for growth and maintenance.

2. The Path of Digestion n Mouth n Esophagus n Stomach n Small intestine n Large intestine n Rectum n Helpers are: liver, gall bladder & pancreas

3. Beginning in the Mouth n Mechanical Digestion begins: –Chewed by the mouth using teeth and tongue –Food is swallowed & squeezed (peristalsis) through the esophagus to the stomach –Churned by stomach muscles

4. Swallowed food enters the Esophagus http://www.endoatlas.com/atlas_es.html

5. Esophagus n Moves food from the back of throat to the stomach n Epiglottis – flap of skin that covers windpipe (trachea), keeping food out of lungs n Valve at the end of the esophagus (sphincter) allows food to pass into the stomach but not back into the esophagus n Takes 8-10 seconds to move bolus (chewed food) from swallowing to stomach

6. From the esophagus to the Stomach

7. Stomach n Muscular walls of stomach contract to churn and mix the food with gastric juices n Gastric juices (hydrochloric acid and pepsin with mucus) - begin the break down of proteins n Chemical and mechanical digestion takes about 2 to 3 hours n Mixture of partially digested food is called chyme

8. Food passes through the pyloric valve from the stomach to the small intestines Close-up of pylorus (pyloric valve) The small intestine is 22 feet long

9. Small Intestine n Chyme is flooded with enzymes n Enzymes help break down the nutrients to basic forms n Liver produces bile (stored in the gall bladder) – a salt that helps break down fats n Villi - finger like projections in the wall of the small intestines where blood vessels absorb nutrients into the bloodstream

10. From the small intestine food passes through a valve to the large intestine http://www.gastrointestinalatlas.com

11. Large Intestine n Undigested material (fiber, water, and un-digestible substances) moves into the large intestine or colon n Water is removed and undigested material reduced to a solid waste called feces n Colon contains bacteria to help final digestion n Feces (yes, poop) is stored in the rectum and eliminated

12. Elimination n Undigested waste is moved into the rectum where it is eliminated through the anus n Peristalsis – the muscular contractions that move food through your digestive system

13. The Liver (& Gall Bladder) n Liver produces bile to help with chemical digestion n Bile stored in the gall bladder (then sent to beginning of small intestine) n The liver filters harmful substances or wastes, turning some of the waste into more bile n The liver helps figure out how many nutrients will go to the rest of the body, and how many will stay behind in storage. – For example, the liver stores certain vitamins and a type of sugar your body uses for energy.

14. Pancreas n Produces some digestive enzymes

15. Chemical Digestion  Mouth - chemical digestion begins in the mouth with saliva (spit)  Stomach - gastric juices (stomach acid, mucus, enzymes) begin to break down the food to smaller molecules  Small intestine – food broken down even more so your body can absorb the nutrients ** Most digestion occurs in the small intestine  Large intestine – bacteria help with final stage of digestion

16. Physical Digestion n Chewing in the mouth using the teeth n Churning in the stomach n Contraction by smooth muscle in the intestine to move food down to the rectum

17. Nutrients n Carbohydrates: starches and sugars; simplest form saccharides n Proteins: simplest form is amino acids n Fats : absorbed as fatty acids (with the help of bile from the liver) n Vitamins & Minerals n Water

18. Enzymes  Enzymes are proteins that help chemical digestion  Enzymes help a chemical reaction without being changed itself  Found in raw fruits and vegetables  Also produced in the stomach, small intestine and pancreas

19. Energy Transformation Chemical energy stored in our food is transformed in digestion to mechanical energy for motion and thermal energy to maintain homeostasis.