in this video we will look at lipoproteins lipoproteins are basically fat lipo and proteins um and there are different types of lipoproteins uh you can say that there are four types these are chly microns vldl very low density lipoproteins LDL low density lipoproteins and HDL high density lipoproteins here I am just drawing how they will be represented in this diagram and if we look at the composition or the amounts of fat and proteins in each of these lipoproteins we can see that the protein content increases from colly microns to the high density lipoproteins basically it means that chly Micron chly microns have a lot of lipids and little proteins LDL low density lipoproteins have a bit more proteins but still mainly lipids and then the high density lipoproteins have nearly half half half proteins half lipids so it is actually important to understand the different protein to lipid ratio in each of these lipoproteins uh because it somewhat relates to their function so for example LDL the low density lipoprotein actually contains a lot of lipids that are cholesterol but we say that this is bad because if we have a lot of ldls it means that we have a lot of cholesterol which is not good um the lipid content of HDL so the lipid content of the high density lipoprotein actually contains less cholesterol and actually is responsible for picking up excess cholesterol from tissue and then bringing it back to the liver and so we say HDL is good so LDL is bad HDL is good in reality though LDL is not that bad it's just when we have high amounts of LDL that it's bad we need LDL we need cholesterol if this doesn't make sense don't worry we will try to follow a story for each of these lipo proteins and see what they do um in our body let us begin with cly microns kly microns are responsible for transporting fats that we have absorbed in our diet and delivering it to body tissues so here we have the stomach and part of the small intestine our diet consists of carbohydrates fats and proteins of course these get digested and then absorbed in the duodenum of the small intestine let us zoom into the small intestine here here I am drawing some intestinal cells and under these cells we have blood vessels on the surface of the small intestinal cells so on the appical side we have a sodium glucose transporter which takes in one glucose for two sodium molecules glucose is then um reabsorbed into the blood the fats in the diet arrive in the small intestine as lipid droplets the lipid droplets are digested and emulsified into m cells which are then absorbed um in into the intestinal cells um as monoglycerides and fatty acids and also cholesterol is absorbed the intestinal cells will then package the monoglycerides fatty acids cholesterol and proteins called apoproteins to form what's known as the cly Micron so all these things are packaged up into colly microns colic is predominantly lipids with little proteins with little Appo proteins the colly microns also contain phospholipids within its structure the colly microns is actually absorbed into the lymphatic system before moving into the blood into the blood vessel via the subclavian vein the colum microns then circulate around the body delivering lipids delivering triglycerides to tissues that need it for energy the remaining remnants of the colum microns will then finish and arrive at the liver so here we have the liver the colly microns will bind onto LDL receptors and will be brought into the hepatic cells okay let us leave the cly microns and look at the other lipoproteins and in order to do this we have to start uh start where we when where we left off with glucose so here we have glucose the liver also receives the glucose that we absorbed earlier it takes it in and through the process known as glycolysis it makes pyruvate pyruvate can move into the mitochondria of the hepy and become a cocoa a siloa can then get transported out of the mitochondria and can be eventually converted to cholesterol using an important enzyme called HMG COA reductase please know that we are missing many chemical reactions but this is just a simple overview so cholesterol is made through a c COA an important reaction step is with the enzyme HMG COA reductase there is actually a cholesterol lowering agent that specifically Targets this enzyme called statins so statins are HMG COA reductase Inhibitors thus stopping the synthesis of cholesterol going back to AIC COA acyoa can also be converted to malan COA to form later fatty acids glycolysis um can also synthesize glycerol when glycerol and one fat and one fatty acid combin they form what's known as mono ail glycerol then with another two fatty acids can form Trias glycerol I only wrote triglycerol to make it fit but to be it's actually meant to be Trias glycerol also known as triglyceride the triglyceride cholesterol as well as apoproteins and phospholipids then can get packaged up through the Golgi apparatus to form a lipoprotein so lipoproteins can look something like this it contains proteins the Appo proteins triglycerides phospholipids and cholesterol the liver cannot actually make all the lipoproteins they actually make two they make either the empty HDL whose main function is picking up excess cholesterol from the body and bringing it back to the liver or the liver can make vldl very low density leop proteins whose main function is for the transportation of fatty acids AIDS transportation of the triglycerides to body tissues remember that vldl and empty HDL have different lipid concentration or composition they are completely different vldl has a lot more lipids especially triglycerides because vldl will go into the blood and transport these triglycerides to body tissues that need it for energy or for storage there is adapost tissue that stores fat and there are tissues that use fatty acids for energy vldl comes across lipases which will Liberate the fatty acids um and this will basically change the vldl to become IDL also known as intermediate density lipoprotein the fatty acids that are liberated can either be stored as triglycerides in tissue or used as energy by some tissues including the hot muscle cells the intermediate density lipoprotein the IDL can be converted um through circulation um to become LDL ll's main function is to transport cholesterol to body tissues this means that it contains uh more a lot a lot more cholesterol than any other lipoproteins so here are some tissues tissues or cells need cholesterol to make hormones um as well as maintaining cell membrane Integrity so after LDL gives the these tissues cholesterol LDL can then return to the liver by binding onto LDL receptors and it gets endos sized so here we have our LDL the LDL can then either be recycled in the Golgi apparatus to make more lipoproteins or can be excreted through bile excess cholesterol gets excreted in bile because the body uh knows not to have M uh knows when there is a lot of cholesterol and so this is one way of basically um excreting cholesterol through bile now finally uh we go to our last Lio protein which is the HDL here we have the empty HDL the empt empty hdl's main function is to pick up excess cholesterol so or cholesterol in general so it enters the circulation um and here we have tissues that have excess cholesterol or cells that have excess cholesterol and the htl will pick up these excess cholesterol and basically return it to the liver the full HDL um with the cholesterol will bind onto a recept receptors called scavenger receptors on the hpat sites and then it will get endos tized the HDL can then either be recycled through the Golgi or excreted depending on how much cholesterol the body needs so that was it um I hope it made sense and I hope you understood the functions of the cly microns the vldl the hair LDL and HDL um and also thank you for watching bye