Ebook Review of medical physiology (27th edition): Part 2
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Ebook Review of medical physiology (27th edition): Part 2
SECTION VGastrointestinal FunctionDigestion & Absorption25INTRODUCTIONThe gastrointestinal system is the portal through which nutritive substances, vi Ebook Review of medical physiology (27th edition): Part 2itamins, minerals, and fluids enter the body. Proteins, fats, and complex carbohydrates arc broken down into absorbable units (digested), principally in the small intestine. The products of digestion and the vitamins, minerals, and water cross the mucosa and enter the lymph or the blood (absorption) Ebook Review of medical physiology (27th edition): Part 2. The digestive and absorptive processes are the subject of this chapter. The details of the functions of the various parts of the gastrointestinal syEbook Review of medical physiology (27th edition): Part 2
stem are considered in Chapter 26.Digestion of rhe major foodstuffs is an orderly process involving the action of a large number of digestive enzymes SECTION VGastrointestinal FunctionDigestion & Absorption25INTRODUCTIONThe gastrointestinal system is the portal through which nutritive substances, vi Ebook Review of medical physiology (27th edition): Part 2ymes from the exocrine portion of the pancreas attack carbohydrates, proteins, lipids, DNA, and RNA. Other enzymes that complete the digestive process arc found in the luminal membranes and the cytoplasm of the cells that line the small intestine. The action of the enzymes is aided by the hydrochlor Ebook Review of medical physiology (27th edition): Part 2ic acid secreted by the stomach and the bile secreted by the liver.The mucosal cells in the small intestine are called enterocytes. In the small intesEbook Review of medical physiology (27th edition): Part 2
tine they have a brush border made up of numerous microvilli lining their apical surface (see figure 26-28). This border is rich in enzymes. It is linSECTION VGastrointestinal FunctionDigestion & Absorption25INTRODUCTIONThe gastrointestinal system is the portal through which nutritive substances, vi Ebook Review of medical physiology (27th edition): Part 2zymes that hydrolyze carbohydrates and peptides, and the glycocalyx is made up in part of the carbohydrate portions of these glycoproteins that extend into the intestinal lumen. Next to the brush border and glycocalyx is an unstirred layer similar to the layer adjacent to other biologic membranes (s Ebook Review of medical physiology (27th edition): Part 2ee Chapter 1). Solutes must diffuse across this layer to reach the mucosal cells. The mucous coat overlying the cells also constitutes a significant bEbook Review of medical physiology (27th edition): Part 2
arrier to diffusion.Most substances pass from the intestinal lumen into the enterocytes and then out of the enterocytes to the interstitial fluid. TheSECTION VGastrointestinal FunctionDigestion & Absorption25INTRODUCTIONThe gastrointestinal system is the portal through which nutritive substances, vi Ebook Review of medical physiology (27th edition): Part 2d lateral cell membranes to the interstitial fluid. The dynamics of transport in all parts of the body are considered in Chapter 1.CARBOHYDRATESDigestionThe principal dietary carbohydrates are polysaccharides, disaccharides, and monosaccharides. Starches (glucose polymers) and their derivatives arc Ebook Review of medical physiology (27th edition): Part 2the only polysaccharides that are digested to any degree in the human gastrointestinal tract. In glycogen, the glucose molecules arc mostly in long chEbook Review of medical physiology (27th edition): Part 2
ains (glucose molecules in 1:4a linkage), but some chain branching is produced by 1:6a linkages; (sec Figure 17-11). Amylopectin, which constitutes 80SECTION VGastrointestinal FunctionDigestion & Absorption25INTRODUCTIONThe gastrointestinal system is the portal through which nutritive substances, vi Ebook Review of medical physiology (27th edition): Part 2as amylose and amylopectin are of plant origin. The disaccharidcs lactose (milk sugar) and sucrose (table sugar) are also ingested, along with the monosaccharides fructose and glucose.In rhe mouth, starch is attacked by salivary a-amy-lase. However, the optimal pH for this enzyme is 6.7, and its act Ebook Review of medical physiology (27th edition): Part 2ion is inhibited by the acidic gastric juice467Table 25-1. Principal digestive enzymes. The corresponding proenzymes are shown in parenrneses.SourceEnEbook Review of medical physiology (27th edition): Part 2
zymeActivatorSubstrateCatalytic Function or ProductsSalivary glandsSalivary a-amylaseCl-StarchHydrolyzes 1:4a linkages, producing a-limit dextrins, maSECTION VGastrointestinal FunctionDigestion & Absorption25INTRODUCTIONThe gastrointestinal system is the portal through which nutritive substances, vi Ebook Review of medical physiology (27th edition): Part 2tidesCleave peptide bonds adjacent to aromatic amino acidsGastric lipaseTriglyceridesFatty acids and glycerolExocrine pancreasTrypsin (trypsinogen)EnteropeptidaseProteins and polypeptidesCleave peptide bonds on carboxyl side of basic amino acids (arginine or lysine)Chymotrypsins (chymotrypsinogens)T Ebook Review of medical physiology (27th edition): Part 2rypsinProteins and polypeptidesCleave peptide bonds on carboxyl side of aromatic amino acidsElastase (proelastase)TrypsinElastin, some other proteinsCEbook Review of medical physiology (27th edition): Part 2
leaves bonds on carboxyl side of aliphatic amino acidsCarboxypeptidase A (procarboxypeptidase A)TrypsinProteins and polypeptidesCleave carboxyl terminSECTION VGastrointestinal FunctionDigestion & Absorption25INTRODUCTIONThe gastrointestinal system is the portal through which nutritive substances, vi Ebook Review of medical physiology (27th edition): Part 2rboxyl terminal amino acids that have basic side chainsColipase (procolipase)TrypsinFat dropletsFacilitates exposure of active site ofpancreatic lipasePancreatic lipase...TriglyceridesMonogfycerides and fatty acidsBile salt-acid lipaseCholesteryl estersCholesterolCholesteryl ester hydrolase...Choles Ebook Review of medical physiology (27th edition): Part 2teryl estersCholesterolPancreatic «-amylaseCl-StarchSame as salivary a-amylaseRibonuclease...RNANucleotidesDeoxyribonuclease...ONANucleotidesPhospholiEbook Review of medical physiology (27th edition): Part 2
pase A2 (prophospholipase A;)TrypsinPhospholipidsFatty acids, lysophospholipidsIntestinal mucosaEnteropeptidase...TrypsinogenTrypsinAminopeptidases...SECTION VGastrointestinal FunctionDigestion & Absorption25INTRODUCTIONThe gastrointestinal system is the portal through which nutritive substances, viSECTION VGastrointestinal FunctionDigestion & Absorption25INTRODUCTIONThe gastrointestinal system is the portal through which nutritive substances, viGọi ngay
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