Biochemistry: Digestion and Absorption
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| Importance of digestion & absorption of carbohydrates? | major component for energy metabolism,
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| What can a high carb diet lead to? | fatty acid synthesis in the liver and eventually increase of fat deposits
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| Importance of digestion & absorption of proteins? | source of amino acids and delivers essential amino acids that humans can't synthsize
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| Child has a plump belly and is malnutritioned. What does plump belly mean? | lack of albumin in blood due to defienct protein diet causes edema in tissues since albumin is required for osmolality
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| Digestion in the mouth? | mastication and salivary alpha amylase (breaks down carbohydrates by cleaving the alpha-1,4 bonds leading to branched oligosaccharides) and lingual lipase (breaks down medium chain TAGs, works in stomach too)
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| Digestion in stomach? | Pepsin, cleaved from pepsinogen due to low pH (<5), cleaves and breaks down proteins into polypeptides. Lingual lipase and gastric lipase work to degrade medium chain TAGs. Carbohydrate digestion stops in the stomach. Low pH: proteins, DNA and RNA
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| Discuss the digestion of lipids found in breast milk | Lipids found in breast milk are medium-chain fatty acids, so they can be digested by the enzymes found in the mouth and stomach (lingual and gastric lipases)
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| What is the optimal activity of pepsin? | pH2
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| What converts pepsinogen to pepsin? | low acid, and pepsin can cleave pepsinogen
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| What is an endopeptidase and give an example | pepsin, cleaves peptide bonds inside of proteins
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| What causes the release of of cholecystokinin and secretin | Production and secretion of chyme into the small intestines leads to the release of the hormones Sscretin and Cholecystokinin (CCK) from intestinal endocrine cells.
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| Function of Secretin? | stimulates release of water and bicarbonate from the pancreas to buffer the chyme and allow pancreatic enzymes to function.
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| Function of cholecystokinin | inhibits gastric mobility, stimulates enteropeptidase activation, activates secretion of pancreatic enzymes and bile secretion from the contraction of the gall bladder.
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| What is the role of HCO3 in pancreatic secretion and bile? | neutralize the pH of chyme to allow pancreatic enzymes to act
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| What are the pancreatic hormones and what cells release them | glucagon (alpha cells), insulin (beta-cells) and somatostatin (gamma-cells)
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| What are the functions of the pancreas | neutralize acid chyme, synthesize digestive enzymes, control intermediate metabolism
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| Function of somatostatin? | inhibitory hormone, suppresses the release of GI hormones like gastrin, CCK, secretin and others
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| Function of pancreatic-alpha amylase | breaks down sucrose, lactose, maltose, isomaltose to disaccharides
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| Function of pancreatic nucleases | digestion of oligonucleotides, nucleosides, free bases, ribose and deoxyribose
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| What cleaves trypsinogen to active trypsin | enterpeptidase
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| What proteins does trypsin activate? | trypsinogen, chyotrypsinogen, pro-elastase, pro-carboxypeptidases, pro-colipase and pro-phospholipase A2
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| Where does trypsin cleave | s lysine, arginine – long narrow active pocket binds positive charge
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| chymotrypsin cleavage sites | at bulky groups (aromatic amino acids – tyrosine, phenylalanine, tryptophan) – wide and large active pocket
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| elastase cleavage sites | glycine, alanine, serine– small active pocket
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| cleavage done by carboxypeptidases | from carboxy end
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| How do the digestive proteases act? | simultaneously on proteins and then after dietary protein is cleaved they cleave eachother
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| Describe autocatylytic pancreatitis | trypsin is abnormally formed from trypsinogen in the pancreas or in the pancreatic duct activating all other zymogens and destroying proteins and membranes of pancreas and duct
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| How does pancreatitis occur? | blockage of pancreatic duct, hypertriacylglycerolemia, ethanol abuse
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| What is a serum marker for pancreatitis? | pancreatic alpha amylase and lipase
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| What can cause acute pancreatitis | migrating gallstones that obstruct the ampulla of Vater
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| How does cystic fibrosis affect the pancreas? | dried mucus caused by protein plugs blocks pancreatic duct and leads to less pancreatic enzymes for digestion of mainly proteins and lipids
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| If only 11% of normal levels of pancreatic alpha amylase is present will carb's be digested? | YES. 10% is sufficient
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| what is the diet for CF patients? | calorie-rich diets:milk or TAGs with medium-chain fatty acids which do not need pancreatic enzymes for digestion.
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| Describe gout | Individuals suffering from gout show high uric acid levels in the blood, and crystals can form that trigger a gout attack
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| Should an individual suffering from gout eat a diet low in purine bases or low in pyrimidine bases | Pyrimidine bases are degraded or taken up into the liver and are harmless for individuals suffering from gout. purine bases are not used by the body and are degraded to uric acid
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| Describe the action of gastrin | hormone that leads to release of hydrochloric acid also named gastric acid (HCl) into the lumen of the stomach by stomach cells
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| What happens when too much antacid drugs are taken | Antacid drugs increase the pH in the stomach juice, and this can lead to less activation of pepsinogen to pepsin. In addition it directly affects the activated pepsin which is optimal active at about pH 2
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| pepsin act mainly as an exopeptidase or an endopeptidase? | Pepsin acts mainly as endopeptidase, which means that it cleaves proteins from the inside and leads mainly to smaller proteins and peptides
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| Which pancreatic enzymes cleaves phospholipids? | phopholipase A2
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| Which pancreatic enzymes cleavescholesterylesters? | cholesterylaesterase
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| Which pancreatic enzymes cleaves triacylglycerols? | pancreatic lipase
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| Where and how are bile salts formed? | in liver by conjugation of bile acids with glycine and taurine
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| Function of bile salts | transport of cholesterol in bile from liver to duodenum, emulsification of dietary lipids for digestion by pancreatic enzymes, uptake of products of lipid digestion into intestinal mucosal cells
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| Properties of bile salts | amphipathic, negatively charged at pH 7
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| Examples of bile salts | glycocholic acid (cholic acid + glycine), taurachenodeoxycholic acid (chenodeoxycholic acid with taurine)
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| where are bile acids made and how? | primary:liver from cholesterol secondary:intestine by bacteria, conjugation of primary and secondary with glycine/taurine done in liver
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| What is required for the digestion of TAGs? | pancreatic lipase needs emulsification of lipid performed by bile salts and lyso-phosphatidylcholine. lipase cleaves TAGs to monoacyl glycerol and fatty acids (which can then enter intestinal mucosal cells)
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| Function of colipase | separates bile salts from the lipid droplet and anchors pancreatic lipase on the water-lipid interface
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| Where in the body is this enzyme synthesized enteropeptidase | Enteropeptidase is synthesized by cells of the duodenum
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| Can pancreatic lipase digest TAGs by itself? | no it needs bile salts and co-lipase
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| Is pancreatic lipase synthesized and transported as a zymogen? | Pancreatic lipase needs as substrate TAGs, which are not found in large quantity in the pancreas.
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| what is the function of the gallbladder | to store and concentrate bile, which contains for example, conjugated bile salts, free cholesterol, phosphatidylcholine and some conjugated bilirubin.
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| What is the percentage of bile acids that are normally brought back to the liver? | 95% of bile acids are brought back to the liver via the portal vein
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| Describe the enterohepatic circulation | The enterohepatic circulation allows the release of conjugated bile salts by the liver into the bile and later on the uptake of unconjugated bile acids from the intestinal lumen via the blood into the liver.
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| Describe cholelithiasis | cholesterol gallstone disease due to decrease of bile salts and PC in bile OR due to increased biliary cholesterol secretion.
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| How is galactose, glucose and fructose taken up into the intestinal mucosal cells | Glucose & galactose is mainly taken up into the intestinal mucosal cells via SGLT (sodium ion cotransport, secondary active transport) and fructose is mainly taken up via GLUT-5 (facilitated transport)
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| What forms sucrose? | glucose and fructose
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| What forms lactose? | glucose and galactose
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| Describe lactose intolerance | Lactose intolerance is a defect related to lack of cleavage of lactose by lactase. Lactose reaches the large intestine and leads there to bloating, diarrhea and dehydration
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| primary lactose intolerance | due to the natural decline of lactase activity from high activity in infants after birth until low activity at about the age of seven years old. Primary lactose intolerance is very common in individuals of Asian, African or Native America heritage.
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| secondary lactose intolerance | due to intestinal injury and loss of lactase or epithelial cells due to severe diarrhea, gastroenteritis or celiac disease
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| Congenital lactase deficiency | is a severe disease that led in the past to death of infants mostly due to severe diarrhea and water loss.
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| How are amino acids taken up into the intestinal mucosal cells | secodnary active transport with several specific transporters (most sodium dependent)
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| How are fatty acids taken up into the intestinal mucosal cells | diffusion of medium chain monoacylglycerol, free fatty acids activated to fatty acyl-CoA, cholesterol diffusion
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| Describe steatorrhea | Steatorrhea leads to less lipid digestion and to fatty, strong smelling feces. It results in loss of lipid-soluble vitamins and dietary essential fatty acids.
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| Causes of steatorrhea | lack of conjugated bile salts needed for lipid digestion,deficiency of enzymes or bicarbonate, or lack of transport, defective intestinal mucosal cells or to less intestinal mucosal cells that are available like after a shortened bowel
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| Why are chylomicrons formed in the intestinal cells | transport of fatty acyl CoA, long chain TAGs, cholesteryl ester
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| Are chylomicrons released into the blood or into the lymph | lymph - apolipoprotein
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