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Lecture 9
Digesting and Absorption
| Question | Answer |
|---|---|
| 3 major foods on which the body lives | carbohydrates, fats, proteins |
| digestion definition | the chemical breakdown of food by enzymes, digestive enzymes are secreted by salivary, gastric, and pancreatic juices |
| absorption definition | movement of nutrients, water, and electrolytes from the lumen of the stomach and intestine into blood (paths) |
| Digestive enzymes: amylase and protease | carbs = starches, protein |
| Digestive enzymes: lipase and sucrase | fats and sugar |
| Digestive enzymes: lactase and maltase | dairy, sugar and malt sugars, grains |
| Carbohydrate Digestion | begins with saliva = salivary amylase, small intestine = pancreatic amylase, 15-30 min after chyme enters the duodenum, maltose |
| Carbohydrate Digestion | enterocytes contain lactase, sucrase, maltase, dextrinase = break down monosaccharides to be absorbed |
| Carbohydrate Absorption: brush border membrane | glucose and galactose; transported against their concentration gradient by Na+ coupled secondary active transport (major mechanism of Na+ absorption); powered by Na+K+ATPase in the basolateal membrane; sodium dependent glucose transporters (SGLTs) |
| Carbohydrate Absorption: fructose | transported by facilitated diffusion in basolateral membrane, cannot be transported against its concentration gradient, facilitative glucose transporters (GLUT2) |
| Protein Digestion | stomach by pepsin = breaks peptide bonds into polypeptides then into peptides |
| Protein Digestion | Polypeptides then move to small intestine where digestion is continued by pancreatic enzymes = trypsin, chymotrypsin, elastase |
| Protein Absorption: brush border membrane | last stage = enterocytes; brush border has microvilli --> peptidase; amino acids transported by facilitated diffusion |
| Protein Digestion flow for stomach and small intestine | stomach: pepsinogen --> pepsin (digestion of proteins) small intestine: trypsinogen --> trypsin --> enzymes (further break down proteins) |
| Lipid Digestion | begins in moth (lingual lipase); stomach (gastric lipase) = chewing and stomach churning break up lipids into smaller pieces |
| Lipid Digestion | stomach empties slowly = allows time for digestion of lipids and fatty foods leave the slowest |
| Lipid Digestion: bile | bile salts and lecithin --> required for absorption -- emulsify lipids into micelles |
| lipid digestion: pancreatic enzymes (pancreatic lipase) | triglycerides |
| Lipid Absorption | lipids are delivered as micelles to the epithelial cells (lipids diffuse into the cells, bile salts remain in the lumen); lipids are resterified into original absorbed lipids |
| Lipid Absorption | packaged into chylomicron with apoprotein B; exocytose from the cell on the basolateral membrane; enter lymph vessels (too big to get into capillaries) |
| Minerals | inorganic elements that come from soil and water |
| Mineral examples | iron, magnesium, potassium, calcium, phosphorus, zinc, copper, iodine, selenium |
| Vitamins | organic elements made by plants and animals |
| Vitamin examples | A, C, D, E, K, B |
| Vitamin absorption depends on ? | solubility |
| Vitamins fat (lipid) soluble | DEAK |
| Vitamins water soluble to know | C, B, B12 |
| Vitamins water soluble absorption | most are absorbed via Na+ dependent secondary active cotransport in small intestine; exception is B12 (cyanobalamin) = susceptible to breakdown by pancreatic enzymes and absorbed in terminal ileum |
| Vitamin B12 ** | stomach parietal cells aid in absorption; intrinsic factor is secreted by gastric parietal cells, IF binds to B12 and protects it from pancreatic enzymes |
| Vitamin B12 gastrectomy and pt** | gastrectomy or injury to the gastric mucosa --> loss of parietal cells --> loss of IF --> patients fail to absorb B12 from the ileum --> B12 deficiency --> pernicious anemia develops (pts lacking IF need to be treated with B12 injections) |
| Lipid(fat) soluble vitamins | DEAK; processed in same manner as dietary lipids (micelles, brush border, chylomicrons) |
| Iron | absorbed across brush border membrane of intestinal epithelial cells; absorbed in duodenum |
| Iron | 70% of total body iron is associated with hemoglobin (Hgb); 3% muscle oxygen-binding protein myoglobin, remainder is in tissue storage form bound to the protein ferritin |
| Iron | in the blood, iron is bound to transferrin = binds and transports iron in the blood |
| Iron | intestinal absorption = free dietary iron is presented in form of Fe3+ --> Fe3 reductase --> Fe2+, Fe2+ absorbed in brush border membrane, can also occur by endocytosis of transferrin in intestinal lumen |
| Iron | iron is essential for RBC formation, primary function of RBCs is oxygen transport (bound to the iron in the heme unit of hemoglobin), iron deficiency --> decreased hemoglobin synthesis --> anemia |
| Carbohydrates products of digestion, site of absorption, mechanism | glucose, galactose, fructose; small intestine; Na+ glucose cotransport and Na+ galactose cotransport and facilitated diffusion |
| Proteins products of digestion, site of absorption, mechanism | amino acids, dipeptides, tripeptides, small intestine, Na+ amino acid cotransport, H+ di/tripeptide cotransport |
| Lipids products of digestion, site of absorption | fatty acids, monogylcerides, cholesterol, small intestine |
| Lipids products mechanism | bile salts form micelles int he small intestine, diffusion of fatty acids, monogylcerides and cholesterol into intestinal cells, reesterification in cell to triglycerides and phospholipids, chylomicrons form in cell and are transferred to lymph |
| Fat soluble vitamins site of absorption, mechanism | small intestine, micelles form with bile salts and products of lipid digestion, diffusion into intestinal cell |
| Water soluble vitamins site of absorption, mechanism | small intestine, Na+ dependent cotransport |
| Vitamin B12 site of absorption, mechanism | ileum, intrinsic factor |
| Bile salts site of absorption, mechanism | ileum, Na+ bile salt cotransport |
| Ca2+ site of absorption, mechanism | small intestine, vitamin D dependent Ca2+ binding protein |
| Fe2+ products of digestion, site of absorption, mechanism | Fe3+ reduced to Fe2+, small intestine, binds to apoferritin in intestinal cell, binds to transferrin in blood |
Created by:
bluedolphin7
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