Understanding Digestion, Absorption, and Transport in the Digestive System

1. Digestion, Absorption, and Transport

2. Overview Digestive System • Functions: Digestion, Absorption, Elimination • Digestion – process of breaking down foods to release nutrients • Goal is to break nutrients into absorbable units • 2 types of digestions: • Mechanical • Enzymatic (chemical)

3. Overview Digestive System • Absorption – movement of nutrients out of GI tract into blood or lymph • Water soluble nutrients  • Fat soluble nutrients  • Excretion – elimination of undigested foods (feces)

4. GI Tract Anatomy

6. Digestive Tract • Layers of GI tract organs • Serosa (outermost) • Interface between GI tract and lymph & blood • Muscle Layers • Longitudinal muscles • Circular muscles • Submucosal and Mucosal and layers (innermost) • Nerves, blood and lymph vessels • Cells of the mucosal layer produce secretions

7. Mouth • Structure – teeth, tongue, salivary glands • Secretions • Saliva • Salivary amylase ….. • Digestion • Mechanical …. • Enzymatic/chemical …. • Swallow  tongue pushes food  pharynx  ……

10. Esophagus • Structure – 12” tube • UES and LES • Function • Transports food from mouth to stomach • Peristalsis and gravity aid food movement • Secretions -- mucus • Digestion • Mechanical (limited) • Enzymatic/chemical – starch digestion continues

12. Stomach • Structure – muscular sack that can expand • extra muscle layer to aid in the mechanical digestion of food (pg 73)

13. Stomach

14. Stomach Related Secretions • Gastrin – hormone that stimulates stomach to release secretions • Hydrochloric Acid (HCl) -- unravels proteins, kills bacteria, activates pepsinogen • Pepsinogen – once activated, begins protein digestion • Mucus – secreted by goblet cells, protects stomach, moistens food

15. Stomach - Digestion • Mechanical • Stomach muscles grind food into a paste called chyme • Enzymatic/chemical • Proteins uncoiled • Protein digestion to polypeptides begins • Starch digestion stops

16. Small Intestine

17. Small Intestine (SI) • Function – The SI is where: • the majority of digestion to absorbable units occurs • Digestion of carbohydrates, fats, and proteins • Vitamins and minerals do not need digestion • Nutrients are absorbed into either capillaries or lacteals

18. Small Intestine

19. The Small Intestinal Villi

20. The Small Intestinal Villi

23. Small Intestine • Digestion - Mechanical • Peristalsis pushes food through SI • Segmentation mixes chyme with digestive enzymes • Also breaks up food mass into smaller masses • Bile emulsifies fats

24. Peristalsis & Segmentation

25. Muscular Action of Digestion Segmentation

26. SI • Absorbed into lacteals (lymph) • Digested fats • Fat soluble vitamins • Cholesterol • Nutrients travel through lymph system to chest area where lymph and blood join • Nutrients enter blood and travel to liver

27. Preparing Nutrients for Transport • Transport pathways • Bloodstream • Water-soluble nutrients and smaller products of fat digestion • Liver • Lymphatic system • Larger fats and fat-soluble vitamins • Chylomicrons • Bypass liver at first

28. The Vascular System • Closed system of vessels • Heart pump • Blood • Delivers oxygen and nutrients • Removes carbon dioxide and wastes • Blood flow • Special routing for digestive system • Liver

30. The Vascular System

31. Large Intestine or Colon

32. Large Intestine or Colon • Undigested foods (fiber) enter into colon • Unabsorbed nutrients pass into colon • E.g. calcium, iron, cholesterol trapped in fiber

33. Colon • Structure • 5-6’ long • Wider diameter than SI • No villi or microvilli • Appendix is a little pouch near beginning of colon • Colon “wraps around” SI

35. Large Intestine or Colon