* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Overview of Lipid Metabolism
Survey
Document related concepts
Epoxyeicosatrienoic acid wikipedia , lookup
15-Hydroxyeicosatetraenoic acid wikipedia , lookup
Low-density lipoprotein wikipedia , lookup
Cholesterol wikipedia , lookup
Ethanol-induced non-lamellar phases in phospholipids wikipedia , lookup
High-density lipoprotein wikipedia , lookup
Phospholipid-derived fatty acids wikipedia , lookup
Transcript
Overview of Lipid Metabolism Learning Objectives By the end of this lecture the students should be able to understand: • Classification of Lipids • The digestion, absorption and utilization of dietary lipids • Lipogenesis and Lipolysis • Lipid malabsorption Classification of lipids Fatty Acids • Fatty acids are long chain carboxylic acids having a terminal carboxyl (COOH-) group – Saturated Fatty Acids: have no double bonds e.g. Palmitic acid and Stearic acid – Unsaturated Fatty Acids: have one or more double bonds • Essential Fatty Acids – Fatty Acids that can not be synthesized de novo and have to supplied in the diet – Linoleic acid – Linolenic acid Triglycerides • When one, two or three fatty acids are esterified to a molecule of glycerol; they form mono, di or triacylglycerols aka TGs • Lipids are stored within adipose tissue as fat droplets made up of TGs Lipogenesis • Lipid synthesis: – From glycerol derived from Dihydroxyacetone phosphate from glycolysis – Occurs in the liver and to a small extent in adipose tissue – Acetyl coA can form any fatty acid except for the essential FA – The main rate limiting enzyme of lipid synthesis is Fatty Acid Synthase Lipolysis • Lipid catabolism where lipids become: – Glycerol – Free fatty acids • Glycerol can be converted to pyruvic acid which enters TCA • Fatty Acids are degraded by beta oxidation, occurs in mitochondria of liver, muscle and adipose tissue The Dietary Lipids • • • An adult consumes about 60-150 g of lipid per day Much of it is composed of Triglycerides Remaining is made up of free Fatty acids, Cholesterol, cholesterol esters and phospholipids Digestion of Dietary Lipids • Digestion begins in the GIT with the action of Lipase • Gastric lipase requires neutral pH to emulsify fat • In adults much of the dietary lipids are transported unchanged to the small intestine owing to acidic pH of the stomach Emulsification of Dietary Lipids • In the small intestine the pancreatic secretions digest the dietary lipids • Bile Salts emulsify fat droplets • Pancreatic lipase digests triglycerides into monoglycerides and free fatty acids • Pancreatic cholesterol esterase digests CE into cholesterol and FFA Absorption of lipids across intestinal mucosa • FFA, cholesterol and monoacylglycrol together with bile salts, constitute micelles to get absorbed across the intestinal mucosal cells • Micelles: amphipathic structures with hydrophobic core containing the water insoluble lipids, and hydrophilic outer shell soluble in aqueous medium of intestinal epithelium Lipid transport from intestinal mucosa • Once inside the intestinal mucosal cells, the absorbed lipids are resynthesized into TG and CE ( cholesterol esters ) • Intestinal cells synthesize apolipoprotein B-48 and package TG and CE into Chylomicrons • Chylomicrons are secreted first into the lymphatics and then into the blood Lipoproteins • TGs and Cholesterol are transported in blood as Lipoproteins. • According to density the lipoproteins are classified as – – – – – Chylomicrons VLDL (very low density lipoproteins ) IDL (intermediate density lipoproteins ) LDL (low density lipoproteins ) HDL (high density lipoproteins ) Classes of lipoproteins with associated Apoproteins Lipoprotein Function Apoprotein Chylomicrons Transport dietary TG and CE from intestine to tissues apoB-48 apoC-II apoE VLDL Transport TG from liver to tissues apoB-48 apoC-II apoE LDL Delivers cholesterol into cells apoB-100 IDL Picks up cholesterol from HDL to become apoE LDL Picked up by liver HDL Picks up cholesterol accumulating in blood apoA1 vessels Lipoproteins and their functions Complex lipids • Phospholipids Polar, amphipathic, ionic compounds composed of alcohol attached to a diacylglycerol or sphingosine • Phosphoglycerides – Phospholipids containing glycerol • Sphingomylin – Phospholipids containing sphingosine • Fatty acid + sphingosine = Ceramide – Glycolipids • • • • Derivatives of ceramide Components of cell membranes Serve as receptors of certain bacterial and viral toxins Antigenic: tumor antigens, embryonal antigens and sources of blood group antigens Cholesterol • Component of cell membranes • Steroid synthesis • Precursor of steroid hormones e.g. corticosteroids, aldosterone, estrogen and testosterone • Vitamin D precursor • bile acid precursor Fat malabsorption • Syndrome of fat malabsorption consists of Diarrhea, steatorria, malabsorption, wasting and vitamin deficiencies • Some common causes are: – Lactase deficiecy – Celiac sprue – Pernicious anemia – Blind loop syndrome – Lymphatic obstruction – Tuberculosis – lymphoma Deficiencies in Fat malabsorption • • • • • Deficiency of Fat soluble vitamins: vitamin A, D, E and K Iron deficiency-Anemia Vitamin B12/ Folate deficiency- Megaloblastic anemia Vitamin K deficiency- easy bruising Vitamin D deficiency- osteopenia