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CHAPTER 18: DIGESTIVE SYSTEM I. Processes of Digestion a. DIGESTION: dissolving and break down of ingested materials (occurs primarily in the first 20- 25% of the small intestine—not in the large intestine) b. Fig 18.1 c. Secretion—release of substances into the GI tract c.i. Exocrine secretion: enzymes, bile, HCl mucous c.i.1. Have large amount of mucous secreted in stomach to protect it from HCl (has high protein content—so not just digest what ingest) c.ii. Endocrine secretion: hormones that regulate digestive system c.ii.1. First isolated and named hormones d. Absorption—movement of molecules produced by digestion from GI tract to the blood or lymph d.i. When digest proteins and carbohydrates, are absorbed into the blood d.ii. When digest fatty acids, are absorbed into the lymphatics e. Motility—smooth muscle contractions that move materials through GI tract and mix contents with various secretions f. Storage and Elimination—temporary storage, elimination and indigestible food molecules II. Digestive System Anatomy a. Folds in the mucosa of (lining of the lumen of the GI tract) form projections called villi (singular=villus) b. Within each villis there are capillaries and a lymphatic vessel called the central lacteal c. Microvilli are formed at the apical surface of each epithelial cell in the villus. When looking at the cells in the light microscope the microvilli give a brush border appearance d. The terms microvilli and brush border are often used interchangeably e. The villi and microvilli increase surface area for absorption. The surface area of the intestine is 600x greater than a tube of the same length and diameter with a flat surface. f. Fig 18.3
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III. Digestion of Carbohydrates a. Carbohydrates a.i. Polysaccharides—made up of a number of subunits a.i.1. Plant starch—long, straight chain of glucose molecules with few branches a.i.2. Glycogen (animal starch)—long chain of glucose molecules with numerous branches a.i.3. Cellulose—complex polysaccharide, partially digested in large intestine by intestinal bacteria (bacteria in large intestine partially digest this fiber, but not well) a.ii. Disaccharides—made up of 2 subunits a.ii.1. Sucrose (table sugar): made up of Glucose-Fructose molecules a.ii.2. Lactose (milk sugar): made up of Glucose-Galactose molecules a.ii.3. Maltose (malt sugar): made up of Glucose-Glucose molecules b. Types of Carbohydrates: b.i. Salivary Amylase—active in mouth and upper portion of stomach b.i.1. Not much digestion occurs between amylase and stomach—not enough time b.i.2. What happens when salivary amylase is exposed to the low pH of the stomach? b.i.2.a.
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This note was uploaded on 02/12/2012 for the course BI 202 taught by Professor Winn during the Fall '10 term at Northern Michigan University.

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