Digestion

1. Digestion Mechanical Digestion (mouth, stomach) Chemical Digestion (mouth, stomach, intestines) Absorption (intestines) Assimilation (at each cell in the body)

3. Sphincters divide the alimentary canal Into separate compartments. Cardiac sphincter Pyloric sphincter Ileocecal sphincter Anal sphinters

4. MOTILITY PERISTALSIS MIXING WAVES

5. Mouth 1. Saliva: Mucous - lubricates food, easier to swallow. Amylase – initiates hydrolysis of starch Lysozyme – bacteriostatic enzyme2. Mastication:3. Epiglottis: cartilage flap that covers the top of the larynx (glottis) Esophagus Muscular tube that propels food to stomach using peristalsis

7. B – Esophagus D – Cardiac Sphincter (esophageal reflux) F – Stomach Muscular, mechanical digestion, also produces bacteriostatic acid, and digestive enzymes H – Pyloric Sphincter (controls flow of food into duodenum)

8. Internal Structure of Stomach Rugae Chief Cells Secrete Digestive Enzymes Parietal Cells Secrete Hydrochloric Acid

9. Pepsinogen – Most Important of the Stomach Enzymes When first secreted, pepsinogen is inactive. When pepsinogen is exposed to HCl, it reacts and converts to Pepsin. Pepsin is the active form of the enzyme. It is a protease. Intrinsic Factor Produced by parietal cells. Essential for absorption of vitamin B12 in the intestine.

10. Control of Gastric Secretions • Smell, sight or taste of food stimulates the vagus nerve to stimulate the stomach. • Increased motility and increased gastric secretions. • Increased release of a hormone called gastrin. • Gastrin stimulates the stomach to produce even more secretions. Peptic Ulcer: a sore in the mucosal lining of the stomach. 90% caused by a bacterial infection.

11. Liver, Gall Bladder and Exocrine Pancreas Liver produces bile. The bile is stored in the gall bladder, and is delivered to the duodenum by the bile duct. Exocrine portion of the pancreas produces digestive enzymes that are carried to the duodenum by the pancreatic duct.

12. Pancreatic Enzymes • Amylase: hydrolyzes starch to maltose • Protease: hydrolyzes proteins to peptides and amino acids • Lipase: hydrolyzes triglycerides (fats and oils) to fatty acids and glycerol • Nucleotidases: hydrolyzes DNA and RNA to form nucleotides

13. Digestion at Duodenum • Role of gastric motility • Role of Bile • Role of pancreatic enzymes • Chemical changes in duodenum (decreased pH)

14. Control of Pancreas and Gall Bladder Cholescystokinin

16. For Absorption to occur, chemically digested nutrients must move through the wall of the intestine and enter the blood circulation or the lymph (lacteal). Mesentery has blood andlymph supply The inner wall of theintestinal lumen is foldedto form villi. Each villus has blood capillaries andlymph vessels.

17. Lymph vessel (lacteal) villi Blood capillaries

18. Muscularis (smooth muscle layer) Serosa (serous membrane) - outermost layer Submucosa(blood vessels, lymph and nerves) Mucosa(mucous membrane) Cells with microvilliand goblet cells

19. Absorption of Lipids 1. In the duodenum, lipids mix with Bile, become emulsified and forms “micelles.” 2. Micelles are taken up by endocytosis andmoved through themucosal cell. 3. While in the mucosalcell proteins are addedto the micelle to makethem more soluble. 4. The new mixture of bile,lipids and protein is called achylomicron. 5. The chylomicron entersthe lymph and is carried away.

20. 8. Chlymycra arecarried in the blood to the liver where theliver converts theminto HDL’s and LDL’sthat are returned to the blood. 7. Lymph vessels empty intothe blood circulation at thesubclavian vein. 6. Chylomicra pass throughlymph nodes and arecarried up the torso to thelymph duct.

21. HDL’s and LDL’s • Lipoproteins- formed by the liver from chylomicra- contain both lipids and proteins • High Density Lipoproteins - “Good Cholesterol”- contain more protein- more soluble in water- tend to remove fatty deposits from blood vessels. • Low Density Lipoproteins – “Bad Cholesterol”- contain less protein, more lipid- tend to add fatty deposits to walls of blood vessels

22. Sugar, Nucleotide and Amino Acid Absorption Active transport processes movethese nutrientsthrough the mucosal cells and into the blood. blood

23. Sugars, amino acids andnucleotides move into the mesentery and are carriedto the liver via the hepatic portal vessel. Liver may store nutrients.Liver may remove toxins. sugars Amino Acids nucleotides

24. The Amazing Liver Stores and Releases Glucose Removes toxins from blood Produces bile Produces blood proteins Stores Lipids and Converts Chylomicra to HDL’s and LDL’s

25. The Large Intestine The ileum is the last segment of the small intestine. It joins the large intestine at the ileocecal sphincter (valve). Below the junction is a small pouch called thececum, and hanging from that is the appendix. The appendix is believed to be avestigial organ because some animals have a very large, functional cecum.

26. Digestive Tract of the Pig In the pig the cecum houses micro-organisms that are essential for the digestion of cellulose (plant fibers). Humans can not digest plant fiber.

27. Large Intestine Function • Each day a typical person swallows about two liters of liquid. • The salivary glands, stomach, pancreas, gall bladder, and intestines add another 6-7 liters of liquid per day. • The large intestines reabsorb that liquid, form a more compact feces, and reabsorb salt. • In diarrhea, bacteria have infected the large intestine and it is no longer able to reabsorb fluids - risk of dehydration.

28. Rectum: stores feces • Anal Sphincters: control defecation