1. Digestive System

2. What is digestion? • Digestion is the conversion of food into small substances that are useful to your body • carbohydrates  monosaccharides • protein  amino acids • lipids  fatty acids & glycerol • Takes place in mouth (oral cavity) & stomach

3. Digestive System Parts Mouth Pharynx Esophagus Stomach Small Intestine Large Intestine Anus • aka. gastrointestinal tract or alimentary canal • Contains accessory organs • i.e. salivary glands, pancreas, liver, gall bladder • Provide enzymes needed for digestion

5. Types of Digestion • Mechanical • Occurs in mouth & stomach • Involves tearing, chewing, grinding, peristalsis • Chemical • Occurs in mouth, stomach, small intestine • Food is coated with saliva which contains digestive enzymes that break down food

6. Parts & Functions DIGESTIVE SYSTEM

7. OralCavity PARTS • Teeth • Tongue • Salivary glands • Pharynx

8. Oral Cavity: Teeth • Carnivores • Enlarged canines for biting & tearing meat • Herbivores • Premolars & molars used to grind & crush rough fibrous plants • Incisors angled for cutting • Ominvores • Eat plants & animals so their teeth resemble both carnivores & herbivores

9. Oral Cavity: Saliva • a fluid/ secretion from the salivary glands • made of digestive enzymes • i.e. amylase  breaks down carbohydrates • Function: to lubricate & breakdown food

10. Oral Cavity: Tongue • Tongue manipulates food during chewing • Helps food form the bolus • Pushes food back to molars for grinding

11. Oral Cavity: Bolus • Bolus = moist ball of food • Easy to swallow b/c it is lubricated • Does not damage esophagus lining & digestive tract • Digested bolus = chyme • Movement of bolus: • Tongue • Roof of mouth • Pharynx • Epiglottis • Esophagus

12. Esophagus • Muscular • Diameter = 2 cm • Connects pharynx & stomach • Cardiac (lower esophageal) sphincter prevents food from going back up the esophagus • Food moves by peristalsis • Wave like muscle contractions that push food along

13. Stomach • What type of digestion takes place in the stomach? • Mechanical: churning • Chemical: gastric juices contain enzymes that breakdown food • Gastric juices are made of HCl & pepsinogen • pH of stomach = 2 • Enzymes in the stomach: pepsin & renin • Pepsin breaks down proteins into a.a. • Renin slows down movement of milk to allow proper digestion

14. Stomach • Pepsinogen • Pepsinogen = inactive pepsin • Pepsin causes proteins to be broken down into a.a  • Hydrochloric Acid (HCl) • Secreted from gastric glands • Sterilizes upper digestive tract & destroys invading microbes • causes the stomach to have a low pH which is optimum pH for pepsin to function • mucous, secreted by mucous cell or gastric gland, protects stomach from HCl

15. Small Intestine • Site of digestion & absorption • 6 m long • Smaller in diameter than large intestine • Secretes intestinal juices • Receives intestinal secretions from pancreas & liver • Ileocaecal valve separates small intestine from large intestine

16. Small Intestine • What is intestinal absorption? • Nutrient absorption through walls of small intestine • Uses active & passive transport Nutrients  intestinal wall  liver  blood  body

17. Small Intestine: Absorption • Villi • Found in the small intestine • 80% of absorption occurs here • are projections of the mucosa into the lumen • Increase surface area for absorption • Why are the villi nestled within capillaries? • For quick absorption of nutrients into blood stream for distribution around body

19. Large Intestine • Function: reabsorption of water, salts, some vitamins • Parts: • Caecum: receives material from small intestine • Colon: ascending, transverse, descending • Rectum: Feces passes through here • Anus:Feces exits here

20. Large Intestine • Chyme enters caeccum near appendix • Appendix was part of lymphatic system • Microorganism that live here help body • i.e. absorption of vitamin K • Feces/stool: final product leaves body from here

21. Factoids • HOW LONG ARE YOUR INTESTINES? At least • 25 feet in an adult. • Be glad you're not a full-grown horse -- their coiled-up intestines are 89 feet long • It takes 3 hours for food to move through the intestine • In your lifetime, your digestive system may handle about 50 tons!!

22. Animations • http://www.medtropolis.com/VBody.asp • http://www.tvdsb.on.ca/westmin/science/sbi3a1/digest/digdiag.htm • http://www.pennhealth.com/health_info/animationplayer/

23. Assignment • TB: Read chapter 3 pages 97 to 99 • Course Package B 25 to B27