HP_C23Notes_Digestive.doc - Human Physiology Notes Chapter 23 – The Digestive System Function and Processes of the Digestive System Moves nutrients

HP_C23Notes_Digestive.doc - Human Physiology Notes Chapter...

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Human Physiology Notes Chapter 23 – The Digestive System Function and Processes of the Digestive System Moves nutrients, water, electrolytes into body using the following processes: o Digestion – macromolecules broken down into component parts , chemical and mechanical o Absorption - transfer of substances from intestinal lumen, through epithelial cells lining lumen, into blood Reabsorption of various ions causes water to follow via osmosis Epithelial cells of intestine have a brush border Cell have microvilli or projections that increase surface area for absorption Carbohydrates absorbed as monosaccharides Amylase Proteins absorbed as amino acids, dipeptides, tripeptides Endopeptidases o Pepsin in stomach o Tyrpsin from pancreas Exopeptidases o From pancreas – cleave off individual amino acids Fats absorbed via simple diffusion Lipase Bile salts combine with lipids to increase surface area for action of lipases Nucleic acids digested into nitrogenous bases and monosaccharides Pancreatic and intestinal enzymes Vitamins and minerals Fat soluble A, D, E, K absorbed in small intestine Water solubles (B and C) move by mediated transport o Motility Peristalsis - muscular contractions move substances through the GI tract Mechanical breakdown Mixing exposes food to digestive enzymes GI smooth muscle contracts spontaneously Smooth muscle surrounds GI tubes o Tonic muscle – can sustain contraction for minutes to hours; found in sphincters and stomach o Phasic muscle – contraction-relaxation cycle last a few seconds; found in stomach and small intestine Slow wave potential – spontaneous cycle of depolarization and repolarization controlled by the enteric nervous system Threshold causes Ca ++ channels to open Ca ++ enters the muscle cells Ca ++ facilitate muscle contraction (Ca ++ -calmodulin) Gap junctions move the impulse through smooth muscle o Secretion Water, ions, digestive enzymes, mucus, moved into the GI tract from surrounding cells (epithelials within GI Tract) and associated organs and glands (salivary glands, pancreas, liver) Removal of wastes Gut-associated lymphoid tissue (GALT) serve immunodefense function Anatomy of the Digestive System
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