{"id":1859,"date":"2020-08-18T13:29:51","date_gmt":"2020-08-18T13:29:51","guid":{"rendered":"https:\/\/meddists.com\/learn\/pre-clinical\/biochemistry\/biochemistry-of-the-metabolism\/lipid-metabolism\/cholesterol-metabolism\/"},"modified":"2021-11-22T23:24:06","modified_gmt":"2021-11-22T21:24:06","slug":"cholesterol-metabolism","status":"publish","type":"page","link":"https:\/\/meddists.com\/learn\/pre-clinical\/biochemistry\/biochemistry-of-the-metabolism\/medical-lipid\/cholesterol-metabolism\/","title":{"rendered":"Cholesterol Metabolism"},"content":{"rendered":"<span class=\"block-heading\" id=\"header_1\">\n<h2 class=\"wp-block-heading\" class=\"wp-block-heading\" class=\"title_collection title1\">Dietary triacylglycerols<\/h2>\n<\/span><span class=\"block-content\" id=\"contents_1\">\n\n\n<div class=\"wp-block-image\"><figure class=\"alignright size-large is-resized\"><a href=\"https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/11\/Lipid41.png\" target=\"_blank\" title=\"Cholesterol Metabolism\"><img loading=\"lazy\" decoding=\"async\" src=\"https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/11\/Lipid41-1024x853.png\" alt=\"\" class=\"wp-image-8348\" width=\"427\" height=\"356\" srcset=\"https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/11\/Lipid41-1024x853.png 1024w, https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/11\/Lipid41-300x250.png 300w, https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/11\/Lipid41-768x640.png 768w, https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/11\/Lipid41-1536x1280.png 1536w, https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/11\/Lipid41-2048x1707.png 2048w, https:\/\/meddists.com\/learn\/wp-content\/uploads\/2021\/11\/Lipid41.png 1600w\" sizes=\"auto, (max-width: 427px) 100vw, 427px\" \/><\/a><figcaption><strong>Figure 1. VLDL, LDL, HDL<\/strong><\/figcaption><\/figure><\/div>\n\n\n\n<p class=\"has-white-background-color has-background wp-block-paragraph\">Dietary TAGs enter the bloodstream in the form of&nbsp;<strong>chylomicrons<\/strong>, which is able to interact with the epithelial cell membrane-bound&nbsp;<strong>lipoprotein lipase&nbsp;<\/strong>in the lumen of the capillaries of various tissues (adipose tissue in particular).<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This lipase hydrolyzes a substantial part (but not all) of the triacylglycerol existing in chylomicrons. The released fatty acids are taken up by the adipocytes, re-esterified with glycerol-3-phosphate (derived from glucose via glycolysis) to form triacylglycerols, and stored as fat droplets within the adipocytes.<\/p>\n\n\n\n<p class=\"has-background wp-block-paragraph\" style=\"background-color:#d2f9e9\"><strong>After the digestion by lipoprotein lipase, chylomicron remnant leftovers are removed from the circulation by the liver.<\/strong> <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Triacylglycerol-containing remnants are hydrolyzed by a lysosomal lipase. The released fatty acids are re-esterified with glycerol-3-phosphate (derived from free glycerol and glucose) to form triacylglycerols. Triacylglycerol is produced from nutritional fat; in this way, along with smaller amounts of triacylglycerol produced by<em> de novo<\/em> synthesis from glucose and amino acids, it is packaged into very-low-density lipoproteins (VLDL) and secreted into the blood (<strong>Figure 1<\/strong>).<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Fatty acids are transported as a physical complex with plasma albumin, but the rest (triglycerides, phospholipids, and cholesterol), require\u00a0<strong>lipoproteins.<\/strong> Their general characteristics are that the hydrophobic lipids are transported in a\u00a0<strong>hydrophilic envelope<\/strong>\u00a0separated from the aqueous medium. This shell is partially composed of proteins, as well as phospholipids whose polar portions face the plasma and end their apolar groups, with cholesterol and other lipids to be delivered, which interact with their apolar parts.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The difference is the lipid: protein content in each lipoprotein, which results in a different density (this increases with the protein content). In ascending order there are (<strong>Figure 2<\/strong>).<\/p>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"pure-table\"><tbody><tr><td>TYPE<\/td><td>COMPONENT<\/td><td>COMPONENT<\/td><td>FUNCTION<\/td><\/tr><tr><td><strong>Chylomicron<\/strong><\/td><td>TG<\/td><td>HIGHEST<\/td><td>Transports the dietary triacylglycerol molecules into peripheral tissues and cholesterol into the liver<\/td><\/tr><tr><td><\/td><td>CHOLESTEROL<\/td><td>LOWEST<\/td><td><\/td><\/tr><tr><td><\/td><td>PROTEIN<\/td><td>LOWEST<\/td><td><\/td><\/tr><tr><td><\/td><td>APOLIPOPROTEIN<\/td><td><strong>B-48, C-II, E<\/strong><\/td><td>The intestinal mucosa produces, the\u00a0 remnants without the triacylglycerol get into the liver with endocytosis<\/td><\/tr><tr><td>VLDL<\/td><td> TG <\/td><td>MEDIATE<\/td><td>Transports the liver&#8217;s triacylglycerols\u00a0 into the extrahepatic tissue<\/td><\/tr><tr><td><\/td><td> CHOLESTEROL <\/td><td>MEDIATE<\/td><td><\/td><\/tr><tr><td><\/td><td> PROTEIN <\/td><td>LOW<\/td><td><\/td><\/tr><tr><td><\/td><td> APOLIPOPROTEIN <\/td><td><strong>B-100, C-II, E<\/strong><\/td><td>Produced by the liver, capillary lipoprotein lipase converts it to LDL<\/td><\/tr><tr><td>LDL<\/td><td> TG  <\/td><td>LOW <\/td><td>Transports cholesterol from the liver into extrahepatic tissues.\u00a0<\/td><\/tr><tr><td><\/td><td> CHOLESTEROL  <\/td><td>HIGHEST<\/td><td><\/td><\/tr><tr><td><\/td><td> PROTEIN  <\/td><td>MEDIATE<\/td><td><\/td><\/tr><tr><td><\/td><td> APOLIPOPROTEIN <\/td><td><strong>B-100<\/strong><\/td><td>Came from VLDL; the target cells are capable of taking it up through LDL receptor-mediated endocytosis. Cholesterol releases, degraded results lower uptake of an excess amount of cholesterol<\/td><\/tr><tr><td>HDL<\/td><td>TG<\/td><td>LOW<\/td><td>Take up cholesterol from different tissues, transport back to the liver, activate LCAT, generating cholesterol-esters. Transports apoC-II, apo-E into nascent chylomicrons and VLDL<\/td><\/tr><tr><td><\/td><td>CHOLESTEROL<\/td><td>MEDIATE<\/td><td><\/td><\/tr><tr><td><\/td><td>PROTEIN<\/td><td>HIGH<\/td><td><\/td><\/tr><tr><td><\/td><td>APOLIPOPROTEIN<\/td><td><strong>A-I, C-II, E<\/strong><\/td><td>Good cholesterol, even high the amount of it even less the risk of atherosclerosis<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n<\/span><span class=\"block-heading\" id=\"header_2\">\n<h2 class=\"wp-block-heading\" class=\"wp-block-heading\" class=\"title_collection title1\"><strong>LDL<\/strong><\/h2>\n<\/span><span class=\"block-content\" id=\"contents_2\">\n\n\n<p class=\"has-background wp-block-paragraph\" style=\"background-color:#ccf6e5\">The circulating VLDLs gradually lose their triglyceride content and apoproteins and then they are referred to as LDLs \u2014 which mainly carry cholesterol ester and apo B-100 receptors. LDL is mainly excreted by the liver, as well as the intestine, the adrenal and the gonads. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">LDL receptors found on tissues are highly important \u2014 they determine the elimination of LDL and cholesterol inclusion. Upon binding, LDL enters the cell through endocytosis, LDL dissociates, receptor recurs the LDL proteins break down in the surface and lysosomal vesicles. Released by cholesterol, which inhibits the synthesis of LDL receptors and de novo synthesis of cholesterol\u00a0 (Inhibition of HMG-CoA reductase) \u2014 prevents large amounts of cholesterol accumulation.<\/p>\n\n\n<\/span><span class=\"block-heading\" id=\"header_3\">\n<h2 class=\"wp-block-heading\" class=\"wp-block-heading\" class=\"title_collection title1\">HDL<\/h2>\n<\/span><span class=\"block-content\" id=\"contents_3\">\n\n\n<p class=\"has-background wp-block-paragraph\" style=\"background-color:#ddfef1\">HDL is of great importance as it plays a role in reverse cholesterol transport \u2014 it carries cholesterol in the liver from the artery wall, extrahepatic cells, where bile acids can be formed. HDL, therefore, provides good cholesterol because it is emulsified \/ VLDL, but does not accumulate as LDL delivered bad cholesterol.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Nascent HDL is secreted from the liver and intestine, its spherical shape is caused by LCAT and apo A-I. The composition of HDL is constantly changing, cholesterol is taken up from other lipoproteins, and it exchanges apoproteins, e.g. or A-II may replace A-I, apo C may be stored. <\/p>\n\n\n\n<p class=\"has-background wp-block-paragraph\" style=\"background-color:#ccfeea\">Triglycerides are obtained from VLDL, and in turn, they give cholesterol esters. After eating the HDL triglyceride content increases. If HDL is reduced, there is a greater risk of atherosclerosis.<\/p>\n\n\n<\/span><span class=\"block-heading\" id=\"header_4\">\n<h2 class=\"wp-block-heading\" class=\"wp-block-heading\" class=\"title_collection title1\">References<\/h2>\n<\/span><span class=\"block-content\" id=\"contents_4\">\n\n\n<p class=\"wp-block-paragraph\">S<span style=\"font-size: revert; color: initial;\">nider MDS. Devlin\u2019s <strong>Textbook of Biochemistry with Clinical Correlations<\/strong>, the 8th Edition. John Wiley &amp; Sons, Incorporated, 2020; 2019.<\/span>  <\/p>\n<\/span><div id=\"the_titles\" style=\"display:none;\"><h2 class=\"wp-block-heading\" class=\"wp-block-heading\">Dietary triacylglycerols<\/h2><h2 class=\"wp-block-heading\" class=\"wp-block-heading\"><strong>LDL<\/strong><\/h2><h2 class=\"wp-block-heading\" class=\"wp-block-heading\">HDL<\/h2><h2 class=\"wp-block-heading\" class=\"wp-block-heading\">References<\/h2><\/div>","protected":false},"excerpt":{"rendered":"<p>Dietary triacylglycerols Dietary TAGs enter the bloodstream in the form of&nbsp;chylomicrons, which is able to interact with the epithelial cell membrane-bound&nbsp;lipoprotein lipase&nbsp;in the lumen of the capillaries of various tissues (adipose tissue in particular). This lipase hydrolyzes a substantial part (but not all) of the triacylglycerol existing in chylomicrons. The released fatty acids are taken [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"parent":1713,"menu_order":4,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-1859","page","type-page","status-publish","hentry"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v28.0 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>Cholesterol Metabolism &#8211; Meddists<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/meddists.com\/learn\/pre-clinical\/biochemistry\/biochemistry-of-the-metabolism\/medical-lipid\/cholesterol-metabolism\/\" \/>\n<meta name=\"twitter:label1\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data1\" content=\"4 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\\\/\\\/schema.org\",\"@graph\":[{\"@type\":\"WebPage\",\"@id\":\"https:\\\/\\\/meddists.com\\\/learn\\\/pre-clinical\\\/biochemistry\\\/biochemistry-of-the-metabolism\\\/medical-lipid\\\/cholesterol-metabolism\\\/\",\"url\":\"https:\\\/\\\/meddists.com\\\/learn\\\/pre-clinical\\\/biochemistry\\\/biochemistry-of-the-metabolism\\\/medical-lipid\\\/cholesterol-metabolism\\\/\",\"name\":\"Cholesterol Metabolism &#8211; 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