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Chapter 28 Structure and Function of the Gastrointestinal System Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins The Job of the Bowel • Food: – Movement – Breakdown – Absorption • Keeping dangerous gut contents out of the blood • Keeping blood contents from being lost into the gut lumen Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Tell whether the following statement is true or false: The mesentery contains the intestine’s blood supply. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer True An extension of the visceral peritoneum, the mesentery contains blood vessels that supply oxygen and nutrients to (arteries) and eliminate CO2 and waste from (veins) the intestines. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Prader-Willi Syndrome • Plasma ghrelin levels are extremely high Discussion: • What are the effects of this disorder? Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Scenario A woman has a pancreatic tumor that secretes gastrin. Question • What complication is likely to develop? Why? Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Scenario • A man cannot produce cholecystokinin. Question • What problems will this cause him? Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Carbohydrate Digestion • Mouth: salivary amylase • Duodenum: pancreatic amylase – Polysaccharides disaccharides • Brush border enzymes – Disaccharides monosaccharides – Monosaccharides absorbed into blood Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Protein Digestion • Stomach: pepsinogen – Activated to pepsin by acid in stomach – Breaks proteins into polypeptides • Duodenum: pancreatic trypsinogen – Activated to trypsin in duodenum – Breaks proteins into polypeptides • Brush border enzymes – Breaks polypeptides into 2–3 amino acid peptides – Peptides absorbed into blood Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Fat Digestion • Duodenum: bile – Emulsifies fats • Duodenum: pancreatic lipase – Breaks triglycerides into glycerol and fatty acids • Jejunum – Packages digested fats as chylomicrons – Passed to the lymph Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Digestion of which substance begins in the mouth? a. Carbohydrates b. Protein c. Fat d. All of the above Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer a. Carbohydrates Carbohydrate digestion begins in the mouth with salivary amylase; protein digestion begins in the stomach with pepsinogen; fat digestion begins in the small intestine with bile and pancreatic lipase. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Discussion Which is the best choice to reduce fat digestion? • Suppress duodenal hormone secretion • Suppress the activity of chief cells in the stomach • Decrease intrinsic factor secretion • Block gall bladder contraction • Inactivate pancreatic lipase Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Question How would fat digestion be affected if bile levels decreased? a. It would increase. b. It would decrease. c. It would have no effect; fat digestion is mainly affected by amylase. d. It would have no effect; fat digestion is mainly affected by lipase. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer b. It would decrease. Bile emulsifies fat so that it can be more easily digested. Decreased amounts of bile would lead to decreased fat emulsification and decreased ability to breakdown/digest fats. Copyright © 2011 Wolters Kluwer Health | Lippincott Williams & Wilkins