1. Human Digestive System

2. All cells need food for growth, energy, and repair. The purpose of the digestive system is to break down the food that we eat into a form that cells can use.

3. Food is broken down in two ways: Mechanical Digestion– when large pieces of food are broken down into smaller pieces through chewing (physical changes) Hydrolysis– enzymes found in saliva with water help to chemically break down the food.

4. Do not need to be digested Need to be digested WaterFats VitaminsProteins MineralsCarbohydrates Nutrients

5. NutrientBroken down into… FatsFatty acids and glycerol ProteinsAmino Acids CarbohydratesGlucose How Nutrients are Broken Down

6. Enzymes are chemicals produced by the digestive system that speed up the rate of chemical changes. Enzymes are specific – enzymes that break down fats will not break down proteins or carbohydrates.

7. The Path That Food Takes 1. Mouth: Teeth break and grind food (physical) Saliva, produced by the salivary glands, contains an enzyme called amylase which breaks down carbohydrates (chemical) In the mouth, mechanical and chemical digestion help to form a ‘bolus’ (the chewed ball of food) to help it transport easier down the esophagus.

8. The Path That Food Takes 2. Epiglottis: is a flap of tissue that closes off access to the trachea when you are swallowing so that food does not go down “the wrong way” when you are talking, the epiglottis covers the esophagus acts as traffic cop directing food and air down their proper tubes

9. The Path That Food Takes, cont’d 3. Esophagus: A tube that connects the mouth to the stomach Peristalsis is the contraction of the esophagus muscles that moves food to the stomach

11. The Path That Food Takes, cont’d 4. Stomach: A muscular bag that produces a protein enzyme called pepsin (chemical) Also produces HCl (hydrochloric acid) which kills microbes and a mucus layer to protect the stomach lining Food is mixed and churned (physical) and chemically broken down to create ‘chyme’ It contains to sphincters (ring of muscles) that open and close allowing food to enter or leave the stomach. Cardiac Sphincter – at the top of the stomach allows food to enter from the esophagus. Pyloric Sphincter – at the bottom of the stomach, allows food to exit and enter the small intestine.

12. The Path That Food Takes, cont’d 5. Small Intestine: A long, hollow tube that produces protein and carbohydrate enzymes (chemical) It’s average size in an adult human is 22 feet long!!! Enzymes from the pancreas and gall bladder enter the small intestine. The majority of absorption of nutrients occurs in the small intestine. Absorption is the process whereby nutrients are absorbed through the lining into the bloodstream. The lining of the small intestine has finger-like projections that aid in the absorption of nutrients by increasing the surface area of the intestinal lining. On each villi are more finger-like projections called microvilli – they help with absorption too!

14. The Path That Food Takes, cont’d 6. Large Intestine (Colon): Food is digested by the time it reaches the colon. Any excess water is removed from the from waste (undigested food), absorbed through the large intestine and returns it to the bloodstream. Contain bacteria (E. coli ) which produce vitamins B 12 and K Produce mucus to help move wastes along

15. The Path That Food Takes, cont’d 7. Rectum: Storage site for solid wastes (feces, stool) 8. Anus: Solid wastes (#2!) exit the body Your digestive system is ~ 5 times longer than you!!

17. Accessory Organs Pancreas – makes fat, protein, and carbohydrate enzymes. Liver – produces bile which physically changes large fat droplets into small ones Gall Bladder – stores bile from the liver

18. Pancreas (under stomach)

19. Absorption Once food has been broken down chemically into a form that is useable by the body, it needs to get to the cells. The inside lining of the small intestine is not smooth, but covered with tiny, finger-like projections called villi (villus –sing.)

20. Absorption, cont’d Each villus contains blood vessels. Digested food particles move from the small intestine into the blood vessels in the villi through the process of diffusion and active transport. Once the food is in the blood vessels, it can be carried to all body cells.

21. Villi Small Intestine Villus Digested food molecules

22. Villi Villus Digested food molecules Blood vessel

23. Villi Villi greatly increase the surface area that comes in contact with the digested food (by 10X). This allows more food to be absorbed into the blood than if the intestine were smooth. Without villi, your small intestine would have to be 70m long to maintain normal absorption!!