1. The Digestive System

3. Purpose of digestive system: –Converts food into small molecules that can be used by cells!! –Why do the food molecules need to be small?? –Four phases: Ingestion  digestion  absorption  elimination

4. Ingestion: process of putting food into your mouth Digestion: process of breaking food down –Mechanical: physical breakdown of large pieces; increases surface area –Chemical: enzymes are used to break food into smaller molecules

5. Absorption: small molecules absorbed by cells in small intestine Elimination: removal of undigestable materials (like cellulose)

6. Mechanical vs Chemical Mechanical: grinding, tearing, peristalsis (churning action)….increases surface area for enzyme action Chemical: enzymes work to make larger molecules into smaller molecules (ex: starch-->simple sugars)

7. Your mouth does both! http://www.hns.org.uk/bio/index.php?option=com_content&view=article&id=123&Itemid=176

8. Mechanical digestion is accomplished by chewing –Your teeth cut, tear, grind, and crush food –Your tongue moves the food around so the tongue can work on it

9. Chemical digestion of mouth –Enzyme=amylase –Amylase begins to break down long starches forming sugars –Saliva also has lysozyme….an enzyme that protects us against bacteria

10. When you swallow the epiglottis covers the windpipe so that you don’t choke!

11. Esophagus Tube connecting throat to stomach Peristalsis: rhythmic contractions of smooth muscles that move food through the digestive system

12. Stomach

13. Large muscular sac Gastric glands release pepsin and HCl Chemical digestion: –Proteins--> smaller polypeptide chains

14. Another gland produces ______mucus_____________ –o This lubricates so food can pass easier and protects the stomach wall –o If acids erode the stomach wall and create a sore it is called a peptic ulcer –o Now scientists know peptic ulcers caused by Helicobacter pylori

15. Mechanical digestion: smooth muscle churns and mixes food –Chyme: mixture with an oatmeal-like consistency

16. Small Intestine Most digestion and all absorption First part of SI= duodenum –Mixes with fluids from the pancreas, the liver and the lining of the SI

17. Pancreas: produces enzymes that break down carbohydrates, proteins, lipids and nucleic acids –Also produces sodium bicarbonate…to neutralize stomach acid

18. Liver and Gallbladder..help in the digestion of fats! Bile: emulsifies fats Bile is made in the liver and stored (released) in the gallbladder

19. Absorption also occurs in SI Structure adapted for this function! Villi: fingerlike projections –Microvilli:tiny projections covering villi

20. Large Intestine Absorbs water from undigested material Bacteria found here help to produce Vitamin K Concentrated waste material: feces Too much water absorbed: constipation If not enough water is absorbed: diarrhea