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Digestive System

Digestive System. Digestive system functions. Ingestion Mixing and movement of food. Peristalysis Digestion of foods. Chemical Mechanical Absorption of digested foods. Defecation. Layers of the GI tract. Alimentary canal vs Accessory organs.

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Digestive System

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  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

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