1. Functions of the Digestive System

2. Ingestion Active, voluntary process Food is placed into the mouth http://blog.americanfeast.com/images/eating-disorder.jpg

3. Propulsion Food is moved from one organ to another Peristalsis – alternating waves of contraction and relaxation of the organ walls (GI tract) Segmentation – food is moved back and forth across the internal wall of the organ.

4. a) Peristalsis b) Segmentation http://www.ptonthenet.com/images/articles/2980_fig01.jpg

5. Food Breakdown: Mechanical Digestion Prepares food for further degradation –Mixing food in the mouth by tongue –Churning food in stomach –Segmentation in small intestine

6. Food Breakdown: Chemical Digestion Sequence of steps where large food molecules are broken down to their building blocks by enzymes –Proteins to amino acids –Lipids to fatty acids and glycerol –Carbohydrates to galactose, glucose, and fructose

7. Absorption Transport of digested end products to the blood or lymph Occurs mainly in the small intestine

8. Defecation Elimination of undigested substances from the body via the anus in the form of feces.

9. Mouth Ingestion Mechanical digestion – teeth breaks down food into smaller pieces Chemical digestion – food is mixed with salivary amylase to begin breaking down starches into maltose

10. Pharynx & Esophagus No digestion occurs Deglutition (swallowing) –Buccal phase – voluntary; mouth to pharynx –Pharyngeal-esophageal phase – involuntary; pharynx to esophagus; peristalsis

11. Stomach – chemical digestion Gastric juices is produced –Protein digesting enzymes (pepsin) –Hydrochloric acid (very low pH) –mucus No absorption except for aspirin and alcohol

12. Stomach - Propulsion Rippling peristalsis occurs in lower half of stomach As the stomach contracts, chyme (partially digested food) is squirted through the pyloric sphincter in small amounts into the duodenum.

13. Small Intestine – Chemical Digestion Proteins and starches are partially digested Fats begins to be digested Brush border enzymes Pancreatic juices – contains many enzymes

14. Pancreatic Juices Complete the digestion of starches Carry out half protein digestion Responsible for fat digestion Digest nucleic acids Contains bicarbonate which neutralizes the acid chyme

15. Small Intestine - Absorption Most substances are absorbed through intestinal cell plasma membrane via active transport. Lipids are absorbed via diffusion Water is also absorbed

16. Small Intestine - Propulsion Peristalsis – waves of contraction moves substances through the intestine Segmentation – mixes chyme with digestive juices and propels food

17. Large Intestines – chemical digestion No digestive enzymes Bacterial metabolizes remaining nutrients releasing methane gas Bacteria makes vitamine K and B

18. Large Intestine - Absorption Some ions Vitamin K and B More water

19. Large Intestine - Propulsion Peristalsis Mass movements – long, slow-moving but powerful contractile waves Defecation reflex – initiated when the rectum’s wall is stretched