Anatomy Review

Anatomy Review - THE DIGESTIVE SYSTEM Topic 5 Digestion and...

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THE DIGESTIVE SYSTEM Topic 5: Digestion and Absorption Graphics are used with permission of: Pearson Education Inc., publishing as Benjamin Cummings ( Page 1: Title Page Chemical digestion involves breaking down food with enzymes into molecules (nutrients, salts, water) that can be absorbed Absorption involves moving those molecules through the GI epithelium and into the blood (most molecules) or lymph (lipids) Page 2: Goals To discuss the action of digestive enzymes (amylases, proteases, lipase) and bile salts To describe trans-epithelial transport of simple sugars (monosaccharides) and amino acids To discuss emulsification, chemical digestion, and absorption of lipids. Page 3: Food is broken down mechanically and chemically Ingested food first is broken down mechanically in the mouth (mastication or chewing) into pieces small enough to be swallowed, and then into even smaller particles in the stomach that can move into the small intestine These small particles contain both major nutrients (a.k.a. macronutrients) and minor nutrients (e.g. minerals) The major nutrients must be broken down enzymatically into their component parts, which then can be absorbed. The major nutrients are: carbohydrates, proteins, lipids
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The main dietary sources of carbohydrates include: starch (a polysaccharide), and the disaccharides sucrose (table sugar), lactose (milk sugar), and maltose (grain or brewer’s sugar) All carbohydrates must be digested enzymatically into their component monosaccharides (the monomers of carbohydrates) for absorption. For example: Starch is digested to glucose monomers Sucrose is digested to one glucose monomer and one fructose monomer Lactose is digested to one glucose monomer and one galactose monomer Maltose is digested to two glucose monomers Proteins (both animal and plant) are digested to amino acids and small peptide chains of two (dipeptides) or three (tripeptides) amino acids Most dietary fat is in the form of neutral fats or triglycerides (a.k.a. triacylglycerols) Each triglyceride molecule is broken down into one monoglyceride (= glycerol + one fatty acid) and two free fatty acids Non-polar products of digestion (e.g. lipid breakdown products) can be absorbed by simple diffusion (passive) through the phospholipids bi-layer of the intestinal epithelial cells; most polar substances are absorbed using either active (i.e. ATP-requiring) or passive carrier-mediated transport mechanisms Page 4: Carbohydrate digestion begins in the mouth Plant starch and glycogen are long polymers of glucose; they are abundant in the diet. Chemical digestion of starch begins in the mouth with the enzyme, salivary amylase (optimal pH ~ 7). Amylase breaks down starch into the following components*:
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Anatomy Review - THE DIGESTIVE SYSTEM Topic 5 Digestion and...

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