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