Ebook Gastrointestinal physiology: Part 2
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Ebook Gastrointestinal physiology: Part 2
https: //k both u Vi en.comChapter 5Physiology of the Liver, Gallbladder and Pancreas: “Getting By” with Some Help from Your Friends5.1IntroductionLip Ebook Gastrointestinal physiology: Part 2pids are necessary for many important processes in the body. Here we discuss how the digestion and absorption of lipids require the adequate synthesis of primary bile acids and bile salts and the circulation of the bile salts between the intestine and the liver (enterohepatic). Let US examine the fu Ebook Gastrointestinal physiology: Part 2nction of the three cell types within the liver as well as the key biosynthetic pathways for bile acids and bile salts in order to better understand tEbook Gastrointestinal physiology: Part 2
heir roles in lipid digestion and absorption.5.2Liver5.2.1Function of the Three Main Cell Types Within the LiverThe three main cell types within the lhttps: //k both u Vi en.comChapter 5Physiology of the Liver, Gallbladder and Pancreas: “Getting By” with Some Help from Your Friends5.1IntroductionLip Ebook Gastrointestinal physiology: Part 2m the bile ducts.Hepatocytes uniquely produce their own structural proteins and intracellular enzymes in addition to fibrinogen, prothrombin group clotting factors, and albumin. Hepatocytes also mainly produce transferrin, glycoproteins, lipoproteins, and ceruloplasmin. The rough endoplasmic reticul Ebook Gastrointestinal physiology: Part 2um, a hepatocyte organelle, is the site of protein synthesis. Once the proteins form, both the smooth reticulum and rough endoplasmic reticulum play aEbook Gastrointestinal physiology: Part 2
role in the secretion of the formed proteins. The endoplasmic reticulum also plays an important role in the conjugation of proteins to carbohydrate ahttps: //k both u Vi en.comChapter 5Physiology of the Liver, Gallbladder and Pancreas: “Getting By” with Some Help from Your Friends5.1IntroductionLip Ebook Gastrointestinal physiology: Part 2ne, the portal system carries the primary dietary carbohydrates (i.c., glucose, fructose, and galactose) to the liver. After uptake by hepatocytes, theseE. Trowers and M. Tischler, Gastrointestinal Physiology,81nni in inn? Am. 1.1 IO.n71A.1-H sCnrinnar lntomntinn'11 Pi.hlỉchỉnn Qit.ic/orUnH 7H 1 /18 Ebook Gastrointestinal physiology: Part 225 Physiology of the Liver. Gallbladder and Pancreas: "Gening...carbohydrates arc converted by cytosolic enzymes into phosphorylated sugars. Glucose rEbook Gastrointestinal physiology: Part 2
eplenishes the stores of glycogen, a glucose polymer. Galactose can be converted into phosphorylated glucose and also be stored as glycogen. Dependinghttps: //k both u Vi en.comChapter 5Physiology of the Liver, Gallbladder and Pancreas: “Getting By” with Some Help from Your Friends5.1IntroductionLip Ebook Gastrointestinal physiology: Part 2portant storage site for iron, vitamin Bl2, and vitamin A.Fatty acids are formed in the liver from excess dietary carbohydrates. Glycerol and fatty acids combine to form triglycerides in the liver. Certain apoproteins arc synthesized in the hepatocytes and arc used in the assembly and export of lipo Ebook Gastrointestinal physiology: Part 2proteins (high density lipoprotein. HDL: very low density lipoprotein, VLDL). The liver synthesizes cholesterol from saturated fatty acids via acetateEbook Gastrointestinal physiology: Part 2
, in the form of acetyl CoA. and serves as the sole site for the formation of bile acids from cholesterol. Other important functions of the hepatocytehttps: //k both u Vi en.comChapter 5Physiology of the Liver, Gallbladder and Pancreas: “Getting By” with Some Help from Your Friends5.1IntroductionLip Ebook Gastrointestinal physiology: Part 2oluble vitamins.The secretion of lipids into the bile is closely related to the metabolism of bile acids, lipoproteins, cholesterol, and phospholipids. The production of gallstones is associated with the biochemical alterations of bile.Hepatocytes detoxify exogenous compounds (e.g., drugs or insecti Ebook Gastrointestinal physiology: Part 2cides) and endogenous compounds (c.g., steroids). During Stage I reactions, the cytochrome P450 enzymes arc involved in metabolic transformations (c.gEbook Gastrointestinal physiology: Part 2
.. hydroxylation or oxidation). Stage II reactions are characterized by the conjugation of Stage 1 metabolites with either glutathione or glucuronic ahttps: //k both u Vi en.comChapter 5Physiology of the Liver, Gallbladder and Pancreas: “Getting By” with Some Help from Your Friends5.1IntroductionLip Ebook Gastrointestinal physiology: Part 2verted into more biologically functional forms via reactions in the hepatocytes.A number of substances (c.g.. drugs or bilirubin) arc conjugated and converted into a more water soluble stale in preparation for excretion via the bile. Thus, when patients with cirrhosis present with a severe decrease Ebook Gastrointestinal physiology: Part 2in liver function, they often encounter serious side effects from small amounts of drugs that cannot be detoxified or excreted. Bile duct cells createEbook Gastrointestinal physiology: Part 2
a tubular conduit for the passage of bile from the liver into the gut. These cells, under the influence of neurohumoral stimulation, alter the water https: //k both u Vi en.comChapter 5Physiology of the Liver, Gallbladder and Pancreas: “Getting By” with Some Help from Your Friends5.1IntroductionLip Ebook Gastrointestinal physiology: Part 2helial cells. Kupffer cells, which arc derived from monocytes, represent the largest group of fixed macrophages found in the body. These cells phagocytose bacteria, old cells, and tumor cells, and make the liver sinusoids a site for the clearance of particulate matter from the plasma. Hence, the liv Ebook Gastrointestinal physiology: Part 2er plays a very important role as a filter.Stellate cells, also known as ho cells or lipocytes, resemble fibroblasts and are relatively small in size.Ebook Gastrointestinal physiology: Part 2
These cells are characterized by having many droplets of fat in their cytoplasm. Stellate cells play an important role in fibrogencsis, w hich is a khttps: //k both u Vi en.comChapter 5Physiology of the Liver, Gallbladder and Pancreas: “Getting By” with Some Help from Your Friends5.1IntroductionLip Ebook Gastrointestinal physiology: Part 2on835.3Formation of Bile Acids and SaltsBile, which is constantly produced by the hepatocytes, is primarily stored in the gallbladder. Approximately 450 mL of bile is secreted in 12 h. The maximum volume of the gallbladder is about 30-60 ml. Due to the continuous absorption of water, sodium, chlorid Ebook Gastrointestinal physiology: Part 2e, and other electrolytes, the bile salts, cholesterol, lecithin, and lipids, which are not reabsorbed, significantly increase their concentrations inEbook Gastrointestinal physiology: Part 2
the bile. Bile salts account for approximately half of the solutes in bile.Bile consists of two key constituents, namely, bile acids and bile salts. https: //k both u Vi en.comChapter 5Physiology of the Liver, Gallbladder and Pancreas: “Getting By” with Some Help from Your Friends5.1IntroductionLip Ebook Gastrointestinal physiology: Part 2id and chcnodcoxycholic acid (Fig. 5.1). Increased production of cholic acid results in feedback inhibition of this biosynthetic pathw ay. Secondary bile acids (deoxycholic acid and lithocholic acid) result from the dehydroxylation of primary bile acids by bacteria when bile containing the primary b Ebook Gastrointestinal physiology: Part 2ile acids is secreted into the intestinal lumen. Bile salts form when bile acids conjugate with either taurine or glycine. Conjugation of taurine withEbook Gastrointestinal physiology: Part 2
cholic acid results in (aurocholic acid. There arc a total of eight possible bile salts. By conjugating bile acids to form bile salts, the p/c, of thhttps: //k both u Vi en.comChapter 5Physiology of the Liver, Gallbladder and Pancreas: “Getting By” with Some Help from Your Friends5.1IntroductionLip Ebook Gastrointestinal physiology: Part 2generally is in the range of 3-5. Because bile acids have a p/c, of ~7 they are almost always fully protonated in their nonionized form and hence are relatively water insoluble. In comparison the p/Cu of bile salts ranges from I to 4. Consequently, bile salts exist primarily in their ionized form (A Ebook Gastrointestinal physiology: Part 2 ) and thus arc water soluble.Reality check 5-1: Patients with Zollinger-Ellison syndrome secrete massive amounts of gastric acid, which enters into tEbook Gastrointestinal physiology: Part 2
heir intestinal lumen. How does the decreased luminal pH affect the role of bile sails' in lipid absorption?5.3.1Recall PointsKey Processes in Bile Achttps: //k both u Vi en.comChapter 5Physiology of the Liver, Gallbladder and Pancreas: “Getting By” with Some Help from Your Friends5.1IntroductionLip Ebook Gastrointestinal physiology: Part 2ile salts exhibit enhanced water solubility in the duodenum.5.4Lipid AbsorptionWhen fatty foods enter the duodenum from the stomach, cholecystokinin (CCK) is released from I cells. CCK stimulates the gallbladder to contract and the sphincter of Oddi to relax (Fig. 5.2). This chain of events occurs a Ebook Gastrointestinal physiology: Part 2bout 30 min after a meal845 Physiology of the Liver. Gallbladder and Pancreas: “Gelling...Fig. 5.1 Biosynthesis of bile acids and bile saltsSecondaryEbook Gastrointestinal physiology: Part 2
Bile AddsIntestinalhttps: //k both u Vi en.comChapter 5Physiology of the Liver, Gallbladder and Pancreas: “Getting By” with Some Help from Your Friends5.1IntroductionLipGọi ngay
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