1. Two Types of Systems Incomplete digestive system –One-way, saclike digestive cavity Complete digestive system –Tube with opening at each end

2. 5 Tasks of Digestive Systems 1. Mechanical processing - break up, mix, and move food material 2. Secretion - of enzymes into tube where digestion occurs 3. Digestion - break down of food particles into smaller molecules

3. 5 Tasks of Digestive Systems 4. Absorption of nutrients and fluids 5. Elimination of wastes and residues

4. Human Digestive System Complete system with many specialized accessory glands and organs About 10 meters long Lined with mucus-secreting epithelium Movement is one way, from mouth to anus

5. Major Components Mouth (oral cavity) Pharynx (throat) Esophagus Gut –Stomach –Small intestine –Large intestine –Rectum –Anus

6. Accessory Organs Salivary glands –Secrete saliva Liver –Secretes bile Gallbladder –Stores and concentrates bile Pancreas –Secretes digestive enzymes

7. Saliva Produced by salivary glands at back of mouth and under tongue Saliva includes –Salivary amylase (enzyme) –Bicarbonate (buffer) –Mucins (bind food into bolus) –Water

8. Structure of Stomach J-shaped organ lies below the diaphragm Sphincters at both ends Outer serosa covers smooth muscle layers Inner layer of glandular epithelium faces lumen mucosa sphincters muscle serosa

9. Stomach Secretions Secreted into lumen (gastric fluid) –Hydrochloric acid (HCl) –Mucus (protective) –Protein-digesting enzymes Stomach cells also secrete the hormone gastrin into the bloodstream

10. Small Intestine Longest segment of digestive tract Receives chyme from stomach Receives secretions from liver, gallbladder, and pancreas Digests food into absorbable subunits

11. Walls of Small Intestine Projections into the intestinal lumen increase the surface area available for absorption one villus

12. mucosa (inner lining) Fig. 24-6a, p.407

13. microvilli at the free surface of an absorptive cell (brush border cell) cytoplasm mucus secretion hormone secretion lysozyme secretion nutrient absorption Fig. 24-6b2, p.407

14. Nutrient Absorption Passage of molecules into internal environment Occurs mainly in small intestine Various methods of absorption –Osmosis, transport proteins, diffusion

15. Large Intestine (Colon) Concentrates and stores feces Actively transports sodium ions out of lumen; water follows Resident bacteria produce vitamins Large and small intestines reclaim 90% of water that enters alimentary

16. Dietary Recommendations Whole foods help prevent chronic disease

17. Vitamins and Minerals Vitamins –Essential organic substances Minerals –Essential inorganic substances