Fat Digestion - Lipolysis & Lipid Transport

welcome back everybody I'm dr. mark today rich and today we're going to talk about the digestion of fats also known as lipolysis and what do we do with all these fat products alright so first let's begin by talking about biting into a delicious cheeseburger and we know that a cheeseburger has proteins fats and carbs there are three major macro molecules of macronutrients today we're just focusing on those fats so when buying into that cheeseburger we're chewing it up mastication swallowing it down our esophagus and it goes into our stomach and from our stomach all the acid will digest it some enzymes will help digest this food stuff and we push it down into our duodenum the first part of our small intestines alright let's just focus on the fats now fats it can pose predominately of triglycerides cholesterol and phospholipids now the triglycerides has tri in it meaning 3 in there's 3 fatty acids in a triglyceride with the glycerol backbone so there's glycerol and three fatty acids now watch my other video that talks about fatty acids because there's many different types you can have short chain medium chain long chain they can be saturated or unsaturated for example now we've got triglyceride so let's write this down coming into our duodenum from our stomach we have triglycerides which I'll write as T G we have cholesterol which I'll write as CH o now the cholesterol that we're taking in from foods can be esterified and they're often known as cholesterol ester but let's just write it as cholesterol now we're also gonna have phospholipids as well and you know what phospholipids are phospholipids make up cell membranes so look at these three products of fat moving throughout Jordan now what happens remember the fact that when you're eating food the proteins are digested in the stomach the carbs that I just did often in the mouth with the amylase and the fats haven't been digested yet until they really reach the stomach to duodenum now that means when you think about when you have a pan at home and you put oil in that pan water in that pan what happens is the oil tends to come together because it's hydrophobic now the lumen of the intestines is filled with water so that fat comes together and forms these big fat globules and that's what happens with these triglycerides cholesterol and also phospholipids so they turn into these big fat globules filled with these things now what we ultimately want to do is make these products small enough so that they can get absorbed through the lumen through the epithelia and then into the circulation of the body so we can distribute these fats around the body but how do we do this when you get these big fat globules the enzymes that we need to break down fat which are lipases can't get to it they need to be smaller emulsified droplets so how do we make a big fat globule into a smaller emulsified tiny little droplet well think about when you are cleaning your pan at home what do you do you're pouring detergent so we need some detergent well thankfully for us we have the gallbladder sitting here underneath the liver now the gallbladder stores bio that the liver produces and we know that bile is made up predominately of water but it's also made up of cholesterol it's made up of bile salts which is probably the most important thing we need to talk about here is those bile salts but how do we get the bile from the gallbladder into the duodenum where all this fat is well what happens is this when fat comes to the duodenum it stimulates a certain type of cell in the walls of the student called entero endocrine cells in taro meaning gut endocrine meaning it's going to release hormones and hormones go into the bloodstream to travel around the body so these fats as they travel through they stimulate the entero endocrine cells and they release two very important hormones one is called kali Sisto können and the other is called secretin secretin is called secretin because it tells stuff to secrete which sounds a bit silly for a hormone because they most of them do that but it was the very first hormone ever to be discovered hence have been called secretin cholecystokinin what's on the name kali Sisto means gall bladder kannan is saying that it's gonna tell it to contract CCK goes to the gall bladder tells it to contract now what does that mean if CCK goes to the gall bladder tells it to contract its going to squeeze the bile that's in the gall bladder down the bile duct and squirt it ultimately into the duodenum perfect why is this perfect because the bile salts within the bile act like a detergent and it emulsifiers this big fat globule into smaller emulsification droplets which can now so there's these smaller droplets which can now be managed by the lipases to come on and chop it up into its smaller sub components so remember triglycerides cholesterol and phospholipids are in these smaller droplets and they're surrounded by these bile salts okay now the question is where are the lipases all right well the lipase is for the duodenum are produced and released by the pancreas so we need to stimulate the pancreas to release lipase anew we do this well very importantly with the help of both CCK and secretin the pancreas is stimulated to release all of its pancreatic juices and pancreatic juices include all the enzymes which are amylase break down camps proteases break down proteins but we're not talking about those two at the moment and also lipase is to break down fats so life phases are now released into the duodenum as well there are those molecular scissors in addition to that it also releases bicarbonate ions now why do we want to release bicarbonate ions from the pancreas into the duodenum well remember the stomach is very acidic a lot of hydrogen ion's and as it goes into the duodenum it can damage the duodenal walls and so we need to neutralize it but in addition to that this is what's important when it comes to digesting fat is that we need a relatively high pH in order for those live paces to chop up fats now if the acid continues through the duodenum it's going to be too acidic the pH is too low so we need bicarbonate to be released from the pancreas and that's going to increase the pH so it's more neutral and we can only properly break down fats in a neutral pH very important because if it's not neutralized what happens is the fats don't break down and it goes out into the fecal material okay that's steatorrhea and we don't want fat in our stall okay so that's one we need it to be basic - we need the lipases to be released three we also need that bile but what's the fourth point that's very important here lipases aren't very good at cutting these fats without help of another molecule and that molecule is co lipase so the pancreas also releases coli Paes and coli players will jump into these emulsification droplets and grab the lipase bring it in and help chop up all the triglycerides so what's the pancreas releasing again the pancreas is going to be releasing coli pay's lipase and bicarbonate amongst other things but this is all we care about at the moment we've got the bile salts from the bar that's come from the gall bladder that's emulsify these big globules into a multiplication droplets the coli pays jumps on pulls in the lipase chops them up now what it chops up is lipase as love to chop up triglycerides and phospholipids okay so what do we break triglycerides up into now if I quickly just draw it up here triglycerides are going to be a glycerol backbone which is that there that's glycerol with three fatty acids what lipase is do especially the pancreatic lipase which are those that were talking about now is it chops that first fatty acid off and it chops that third fatty acid off which leaves us with two fatty acids and a fatty acid attached to a glycerol that's the second fatty acid which is caught and it's a 1 x 2 monoglyceride all right so the lipase is give us two fatty acids this is for every triglyceride 2 fatty acids and 1/2 monoglyceride it also goes to the phospholipids and helps break them up to release in their fatty acids free fatty acids ok so now what we have floating around the duodenum fatty acids cholesterol and monoglycerides now what these need to do is they need to be surrounded by the bile salts again this is very important because again what the bile salts do is act like a detergent so it's going to have a component that loves fats which you'll hold on to the fatty acids cholesterol and monoglycerides and a component that loves water which will be exposed to the external environment now what will happen is these products which are now called miss seals or my seals which are very small around about 40 nanometers okay in diameter not very large these mussels will travel and it needs to move its way through it moves through the lumen of the duodenum or small intestines needs to move through the wall of the epithelia into being tara sites or the epithelial cells of the intestine okay so how does it do it as it pushes its way through it leaves behind the bile salts which get reabsorbed or excreted and it pushes through the fatty acids the cholesterol and the monoglycerides okay into being tara site which is the epithelial cell of the intestine now another important point is this the lumen the wall of the lumen has a water layer and this water layer can actually inhibit some long-chain fatty acids from coming through into the intera site which means some long-chain fatty acids continue through into the colon which is the large intestines but luckily we have bacteria that can help break these fatty acids down the other thing that's very important is that the luminal wall here is quite acidic now the reason why it's acidic you're probably thinking but didn't really release bicarbonate that should neutralize it well the luminol wall is quite acidic because these antara sites have sodium hydrogen ion exchanges so sodium proton exchanges it Chuck's our sodium in throws a proton out which makes it slightly acidic why is that important well the acid breaks up the my seals which means throws away those bile salts and actually facilitates the fatty acids cholesterol and also the monoglycerides into the intera site alright so what we now have is these fatty acids cholesterol and monoglycerides in the intera site what happens now well because this is a cell it's going to have organelles and we know that one very important organelle is the endoplasmic reticulum all right so the endoplasmic reticulum what it's going to do is we know that likes the synthesize products it likes to the smooth endoplasmic reticulum likes to synthesize lipids and so it actually takes on board fatty acids cholesterol mana glycerides and actually builds them back up into triglycerides and cholesterol so what ends up spitting out is triglycerides and cholesterol all right so now I've got triglycerides and cholesterol it starts to move through the Golgi apparatus the Golgi apparatus remember is the packaging system of the body so then moves into the Golgi apparatus and what it does here is it then forms it into something called a chylomicron this is a package and by doing this forming it into something called a chylomicron it exports out this column icon so let's draw it up karla micron is called a lipoprotein it's fats and proteins the fats are the triglycerides and cholesterol and some phospholipids and the protein is basically this shell now this shell okay inside like I said you're gonna have triglycerides and cholesterol and forming the outside of the shell is going to be phospholipids but also proteins and the very important protein you need to remember here is a PO b48 this is the major protein that sits on the outside here like a hat draw it like a hat this is a PO B and it's number 48 okay so this is what forms a lot of this shell of this Lippo protein now what you can see is this is formed by the Golgi apparatus pushed out now what's it pushed out into it's actually pushed out into the lymph so now I want you to think about how digesting fats is different to digesting carbs and proteins because when we digest carbs and proteins by the time they get to the small intestines and they're absorbed into the intera science they are subsequently absorbed into the bloodstream and that blood stream is part of the portal system and goes to the liver for processing but for fats it does not do that this chylomicron jumps into the lymph and the lymph will travel up through the thoracic duct now remember you're going to have that lymph thoracic duct depending on which side it's going to enter into the sub whether it's the left or right subclavian here I've drawn it with the lymph free entering the venous system on the left subclavian which means now the facts in this column are chrome with a PO b48 on the outside is now moving its way through our blood stream so let's draw it up again we've got the a PO be 48 and then inside we'll get the triglycerides and cholesterol and now it's moving through our bloodstream now what happens is this as it moves through the bloodstream it will bind to very specific receptors and these lippo protein lipases allow for this column icon to bind Lippo protein lipase --is a present which break down the triglycerides that are inside these chylomicrons that's right Carla Mike run down just in case chylomicron and it breaks down the lipoprotein lipase is break down the triglycerides again into fatty acids and monoglycerides the fatty acids and monoglycerides are moving to peripheral tissues these peripheral tissues are predominately skeletal muscle if it is skeletal muscle these fatty acids and monoglycerides are used for energy production if they move into a deeper science which are lipid containing cells they are there for storage okay now what that means is these chylomicrons and now reduced in triglycerides they're not fully empty of triglycerides but they're reduced but they are high in cholesterol now because these are deeper sites in skeletal muscle then they don't require so much cholesterol what we want to now do is take what we call carlo micro remnants now which are what these are called which are high cholesterol back to the liver and so via the bloodstream they go back all the way to the liver and the liver can process this cholesterol okay now another important point is this this is where we start moving into talking about vldls IDL's LDLs and HDL they VL Dells very low density lipoproteins so Karla micron is a lipoprotein but it's a very large lipoprotein that is produced after eating in the absorptive state after you've just had a meal Karla microns are produced that contain triglycerides and cholesterol from the food that you've ingested and the lipoprotein or the appo protein is a po b48 and it travels to the periphery to give off triglycerides the remaining cholesterol goes goes back to the liver for processing but in times of fasting what happens is you create more lipoproteins now they're not chylomicrons they're smaller than chylomicrons but similar they're produced in the liver the first one that's produced during fasting is one that's called a very low density lipoprotein it looks like this color makan but smaller it doesn't have a per b48 but it has a PO b100 as its hat and then it goes from the liver containing triglycerides and cholesterol that the body has made or stored right and delivers it out to the tissues of the body now once it's delivered out this very low-density lipoproteins delivered out this triglycerides it's now high in cholesterol low and triglyceride and that's called an intermediate density lipoprotein or a low-density lipoprotein now you've probably heard that these LDLs or ideals have high cholesterol and they love distributing cholesterol to the tissues of the body and they love to deposit cholesterol to your blood vessels and this is where we start to get that increased risk of vascular disease because it deposits the question on this sub endothelial regions this is underneath the walls of the blood vessel which causes inflammation and damage of the vessel and ultimately atherosclerosis so what's the recap this is the recap you ingest fats those fats travel into the duodenum now there's some lingual lipase --is that break down a little bit of fat there's some gastric lipase that break down fats and then you've got predominantly pancreatic lipase errs which break down fats but they can't break down fats because they're in this big fat globule that's formed because of all the water that's inside the duodenum so cc-can secretin stimulate the gallbladder to release bile bile and bile salts emulsifies the fact gob globule into these emulsification droplets these are multiplication droplets now with coli paise that's released from the pancreas have coat lipase attached to them pulls in the lipase that's also released from the pancreas remember bicarbonates also release to increase the pH and make it neutral so we can do all these processes chop up the triglycerides into free fatty acids and monoglycerides these free fatty acids and monoglycerides are surrounded again by the bile salts for my seals these my seals will then go to the walls the luminal walls of the intestines where the acidic layer this very fine acidic lay produced by sodium proton pumps push away the bile salts and pull in the fatty acids monoglycerides and cholesterol the free fatty acids monoglycerides in cholesterol jump into the smooth endoplasmic reticulum where they're turned back into triglycerides and cholesterol they're then packaged by the golgi into carla microns and the chylomicrons that are packaged have a PO b48 as the apolipoprotein that forms this hole a PO protein that jumps into the lymphatic system via the thoracic duct jumps back into the bloodstream by the subclavian moves through the bloodstream will bind to tissues predominately skeletal muscle and adipocytes where it breaks down via lipoprotein lipase 'as the triglycerides into again the free fatty acids and monoglycerides colloidal muscle to be used as energy or a Dipper sites to be stored as energy right as fat which is energy and the remaining cholesterol in these what's now called chylomicron remnants travel back via the bloodstream to the liver with a cholesterol can be metabolized now what do we use cholesterol for we use cholesterol to to create cell membranes we use it to create steroid hormones such as those of the adrenals and gonads what ends up happening now at the liver is that the cholesterol that's been stored and used if it's the time of fasting we start to produce not chylomicrons but smaller Carla microns one that's called VLDL that doesn't have a PO B 48 but has a PO be 100 and that thing goes distributes stored triglycerides and cholesterol to the tissues of the body okay and sometimes the the remaining product of the VLDL which is the ideal or the LDL can deliver these excessive amounts of cholesterol to the blood vessels and form atherosclerosis so there we go that's the digestion of fats

Channel: Dr Matt & Dr Mike

Views: 110,510

Keywords: ldl, idl, hdl, vldl, chylomicron, fat metabolism, fat digestion, lipolysis, cholesterol, lipids, fats, triglyceride, monoglyceride, fatty acids, LCFA, SCFA, lipase, pancreas, cck, secretin, colipase

Id: n-TsZLIR6Is

Length: 23min 27sec (1407 seconds)

Published: Wed Nov 28 2018