The Four Stages of Food Processing

1. The Four Stages of Food Processing • Ingestion • Is another word for eating • Digestion • Is the breakdown of food to small molecules • Absorption • Is the uptake of the small nutrient molecules by the body’s cells • Elimination • Is the disposal of undigested materials from the food we eat

2. Mechanical digestion • Begins the process • Involves physical processes like chewing Increases the surface to volume ratio of food particles but it does not break the chemical bonds within a food molecule

3. Chemical Digestion:enzymes and H2O used to break chemical bonds Hydrolase (pepsin) Amino acid Protein Sugar Hydrolase (amylase) Fatty acid Glycerol Hydrolase (lipase) Figure 22.4b

4. Anatomy of oral cavity (mouth)

5. The major salivary glands

6. Esophagus- delivers food to stomach

7. Anatomy of the Stomach • Stores and begins the chemical breakdown of food into chyme (creamy paste) • Parts include the cardiac, fundus, pyloris • Sphincters at both ends • Rugae to allow expansion

8. Stomach- specialized structure for further chemical digestion Enzymes target proteins and lipids

9. Anatomy of the stomach

10. Histology of the Stomach • Oblique musculature allows food to by churned while being moved • Gastric pits with gastric glands: secrete gastric juice • Mucous neck cells: Acidic mucous • Parietal (oxynetic) cells: HCl and intrinsic factor (for B12 absorbtion in SI) • Chief (zygomatic) cells: Pepsin (protein digestion) • Enteroendocrine cells: Hormones to regulate digestion • gastrin • histamine • endorphins • serotonin • cholecystokinin • somatistatin

11. Microscopic anatomy of the stomach

12. Peristaltic waves

13. Small intestine – Primary site of absorption of digested molecules

14. The small intestine • Three regions • Duodenum • Ileum • Jejunum

15. Duodenum-upper portion still receives some digestive enzymes • Is the first part of the small intestine • Receives digestive agents from several organs Fats are emulsified for absorption Pancreas- neutralizes acids from stomach Bile Liver Gallbladder Bile Acid chyme Pancreatic juice Duodenum of small intestine Pancreas

16. The jejunum and ileum • Are parts of the small intestine • Are specialized for absorption Nutrient absorption Nutrient absorption Blood vessels Microvilli Epithelial cells Interior of intestine Muscle layers Blood capillaries Villi Lymphatic vessel Epithelial cells Nutrient absorption Intestinal wall Villi

17. Liver and Gall Bladder • Liver: Produce Bile (emulsifies fat) • Gall Bladder: Stores Bile • Liver • Liver lobules (sexagonal) with hepatocytes • Portal triad at each corner (Hepatic artery, HPV, and Bile Duct) • Liver sinusoids with macrophages (Kupffer cells) that remove bacteria and worn RBC’s

18. Microscopic anatomy of the liver

19. Bile • Yellow-green alkaline solution that emulsifies fat • Bile salts, bile pigments, cholesterol, neutral fats, phospholipids (lecithin, etc.) and electrolytes • Bile salt: Cholic acid and chenodeoxycholic acid (cholesterol derivatives) emulsify fats. Recycled rather than secreted by the enterohepatic circulation

20. Role of bile salts & fat emulsification

21. Gall Bladder • Stores, but does not produce, bile • Bile from hepatic ducts enters through a cystic duct to the GB. Upon stimulation, bile leaves the cystic duct, to the common bile duct (cbd) and goes to the duodenum of the SI • Major stimulus: CCK (cholecystokinin) from SI causes contraction (released when fat detected)

22. Pancreas • Secretes enzymes (in pancreatic juice) for the breakdown of proteins and other foodstuffs • Enters via the main pancreatic duct • Pancreas has acini, whose cells are filled with zymogen granules (enzymes)

23. Structure of acinar tissue of the pancreas

24. Pancreatic juice • Water, enzymes, and electrolytes (primarily bicarbonate). Helps neutralize chyme. • Enzymes are released inactive, which activate under the proper pH preventing self-digestion. • Pancreatic enzymes (amylase, lipase, nuclease) may be active, but require ions or bile for optimal activity

25. The Large Intestine • Function is to absorb water, not nutrients, from fluid state chyme and secrete a semisolid feces • Three unique characteristics • Teniae coli: three bands of smooth muscle • Haustra: pocket-like sacs created by muscle bands • Epiploic appendages: fat filled pouches of the visceral peritoneum (function unknown)

26. Colon: Large intestine- absorption of water.

27. Colon: rectum – specialized region for temporary storage Anus – exit from digestive system- separate exit from the urogenital system