Digestive System

1. Digestive System

2. Digestive system functions • Ingestion • Mixing and movement of food. • Peristalysis • Digestion of foods. • Chemical • Mechanical • Absorption of digested foods. • Defecation.

3. Layers of the GI tract • Alimentary canal vs Accessory organs. • Wall of GI tract is composed of four layers (inside->outside) • Mucosa • Submucosa • Muscularis • Serosa • Peritoneum • Mesentery

4. Layers of the GI tract

5. Tortora 516 Salivary Glands • Saliva is secreted from 3 pairs of glands • Parotid glands (back) • Submandibular glands (jaw) • Sublingual (below tongue) • Composition of saliva: • 99.5% water • 0.5% solutes • Salivary amylase- (digestive enzyme for starch) • Mucus (lubrication) • lysozyme (kills bacteria)

6. Control of Salivary Glands • Parasympathetic ANS stimulates production of saliva. • Stimuli: • Food touching the tongue • Smell • Taste • Thought of food.

7. Chewing • Mechanical digestion involves • Muscular manipulation by the tongue • Teeth grind food into smaller pieces • Saliva mixes in Result: a soft, flexible, easily swallowed mass called a bolus

8. Tortora Pages 519-520 Swallowing • Voluntary stage • Bolus is pushed to back of mouth by tongue. • Pharyngeal stage • Breathing stops. • Bolus passes through pharynx • Esophageal stage • Peristalysis • Heartburn

9. Tortora Pages 518-520 Esophagus • Connects mouth to stomach. • Lies behind the trachea (flat side) • Passes through the diaphragm • Contains two layers of smooth muscle. • Food has to pass over trachea @ epiglottis

10. 520-521 Stomach • J shaped, lies under diaphragm. • A mixing chamber and holding reservoir- size varies • Divided into four areas: • Cardia • Fundus • Body • Pylorus/ Pyloric sphincter • Rugae

11. Tortora Pages 439-443 Wall of Stomach • 4 layers: • Mucosa • Submucosa • Muscularis: 3 layers of muscle • Longitudinal layer • Circular layer • Oblique layer • Serosa

12. Tortora Page 522 Gastric Gland secretions • Mucous cells • Mucus • Chief cells • Pepsinogen • Parietal Cells • HCL • Intrinsic factor (B12) • G cells • Gastrin (hormone)

13. Tortora 522-523 Stomach & Digestion • Mechanical digestion • Bolus converted to chyme. • Mixing waves push chyme into duodenum. • Pyloric sphincter releases into SI • Chemical digestion • Pepsin breaks down proteins into peptides. • Lipase digests triglycerides (in acid) into diglycerides

14. Tortora 523 Stomach & Absorption • Mucus protects the stomach lining from being digested itself • Little absorption of nutrients here • Stomach wall does absorb: • Water • Electrolytes • Some drugs (aspirin) • Alcohol

15. Tortora 523 Pancreas • Pancreas lies behind the stomach • Secretions pass through pancreatic duct into duodenum • Pancreatic juice:Bicarbonate counteracts acid from chyme • Digestive enzymes • Islets of Langerhans produce hormones: insulin

16. Enzymes produced by the pancreas that work in the small intestine: • Pancreatic amylase – turns starches to dissacharides • Trypsin - proteins to polypeptides. • Chymotrypsin - proteins to peptides. • Carboxypeptidase - proteins to peptides. • Pancreatic lipase - triglycerides to fatty acids & monoglcerides • Ribonuclease -nucleic acid digestion

17. Tortora 524-525 Liver • Heaviest gland in the body: 3 lbs. • Involved in filtration, storage (glycogen), protein metabolism, and excretion • Produces bile • Emulsifies lipids (fats) • Bile leaves liver through cystic duct.

18. Tortora 525-526 Gall Bladder • Bile (made in the liver) is stored in the gall bladder. • Carried by cystic duct to common bile duct, then released into duodenum. • Bile emulsifies lipids Gall stones (crystallized cholesterol)

19. Tortora 526-527 Small Intestine • Composed of • Duodenum • Jejunum • Ileum • Food is released through ileocecal sphincter into the cecum

20. Small Intestine • Villi extend from wall of sm intestine. • Mucosa • Capillary network • Lacteal • Small intestine gland. • microrvilli

21. Enzymes produced by small intestine • Maltase maltose to glucose • Sucrase sucrose to glucose & fructose • Lactase lactose to glucose & galactose • Peptidases peptides to amino acids • Ribonuclease RNA to sugar & bases • Deoxyribonuclease DNA to sugar & bases

22. Tortora 530 Absorption in the Small Intestine • Carbohydrates & Proteins move into capillaries. • Fatty acids & monoglycerides move into the lacteal.

23. Tortora 532-533 Large Intestine/ colon • 5 ft in length/2.5 inches diameter • Ileocecal sphincter: allows material to pass from sm. intestine to the colon • Has ascending, transverse, descending, and sigmoid portions. • Puckered due to contraction of muscular bands (teniae coli)

24. Digestion and absorption • Bacteria ferment & digest food- releasing H2, CO2, methane gases (flatulence) • Bacteria produce vitamin B & K(absorbed) • Bacteria break down bilirubin- brown color • Absorbs much of the waterand ions, forming feces.

25. Tortora 532 Appendix • Structure: • Short finger-like extension of the lg. intestine • Attaches to the cecum • Stores a sample of healthy colon bacteria, to re-colonize the colon after an intestinal disease. Appendicitis: inflammation requiring removal of the appendix

26. Inflamed appendix

27. Tortora 533-534 Defecation reflex • Mass peristalysispushes contents from the sigmoid colon to the rectum • Stretch receptors initiate the defecation reflex • Initiated by food in the stomach/ ANS • Internal sphincter- (involuntary) opens • External sphincter (voluntary control) + downward pushing of the diaphragm push out the feces

28. Colon cancer Healthy colon • One of the deadliest cancers • Detected by stool samples, or sigmoid/colonoscopies • Polyp removal using a wire snare