welcome back to the dirty medicine dirty biochemistry series in the next few videos I'm going to be teaching you what I believe is the most challenging topic in all of biochemistry I'm speaking of course about lipid transport now if you've cracked open a review textbook or maybe you've you know meandered through different question banks you've probably seen a bunch of terms that you know mentally are all connected to lipid transport because you weren't sleeping for that long in the first two years of medical school and they try to teach you biochemistry and your brain knows that all of these terms have something to do with fat right they have something to do with lipids you know that they're important for the biochemistry of lipid transport but unfortunately if you take a look at the review resources out there there's really nothing in my humble opinion that teaches you what you need to know about lipid transport in terms of both the biochemistry but also the high yields what I'm saying is that there are some resources that oversimplify this topic and they just throw a diagram on a piece of paper and expect you to get questions right on test day there are other resources that are hundreds of pages long and these are usually your biochemistry textbooks which break down this pathway for you but they do so in such an overly detailed manner that you get lost in those details and can't keep in mind the high yield what do I need to know for test day ideas so my goal with this with this video in the next few videos is to first teach you the biochemistry but to do so with the perfect balance of detail and big picture in mind it's really really easy to get lost in lipid transport if you're oversimplifying and not putting in enough detail but it's also easy to get overwhelmed and have a panic attack if you're doing this with the lens of a biochemist so dirty medicine has got you covered I'm going to teach you everything that you need to know about lipid transport and I'm going to do so efficiently so that when we're done you will absolutely know the pathway but you're not going to get lost in the details and the reason that that approach is important is because when I'm done teaching you this pathway you'll be able to connect the biochemistry that you should have learned in the first two years of medical school you'll be able to connect that to the high yield concepts that they're gonna ask you on USMLE and comlex in other words I'm gonna teach you everything you need to know and absolutely nothing more so let's get started with lipid transport now look at this list of terms triglycerides micelles chylomicrons LDL HDL VLDL ideal LPL HSL I mean have you had enough eles yet lipase lecithin cholesterol acyl transferase Apryl lipoprotein a 1b 48 e 100 C 2 and E what language am i speaking right now guys I mean seriously this is confusing stuff and if you're looking at this list and you're probably like most medical students in the world you're saying to yourself oh my god I don't know what each of these things do how the hell am I gonna get these questions right on test day in other words you're like our girl Princess Leia help me dirty medicine you're my only hope well don't worry guys today I'm going to simplify this exhaustive list of terms teach you some high-yield biochemical pathways as it relates to lipids and wrap all of that up for your studying pleasure and tell you what you need to know to get the questions right on test day so this is part one of lipid transport and because this topic is so complex and so detailed I need to break it up into multiple videos as to not overwhelm you if I put all this stuff into one video you'll go home crying and that's not my goal I want you to score the highest possible score on your USMLE and comlex so this is part one and in this video we're going to be discussing everything that happens from the moment that a dietary fat enters the system up until the point that a chylomicron is formed everything in between of what I just said is going to be what we talked about in this video's biochemical pathway so let's get started with where the system starts right dietary fats so from the moment that you take that bite of a cheeseburger or you take a bite of your Zeki organic bread avocado toast if you're one of those type of people the moment that dietary fat enters your system it immediately starts being packaged and broken down the first thing that acts on it is salivary lipase so you probably know that there's lipase that's secreted by the pancreas and lipase breaks down fat remember that the suffix ace ASD means to break something down so lipase breaks down lipids right it aces lipids so it breaks down lipids now lipase is obviously secreted by the pancreas this is something that's high-yield and that you learn when you're doing GI but there's also lipase in the saliva now the lipase in the saliva is certainly not as potent it's not as strong but it still breaks down fats nonetheless so as soon as you take a bite of something that has dietary fats the saliva is already trying to prepackaged those dietary fats into the necessary breakdown products for ultimate packaging and transportation so dietary fat gets broken down initially to some extent by salivary lipase and when that happens it's broken into free fatty acids monoglycerides and cholesterol additionally there could be other products in here such as fat soluble vitamins etc but this is what you should keep in mind now once we have these components obviously you're swallowing and the food bolus will go down your esophagus go through your stomach and into the small intestine now in the small intestine these compounds and these components are going to be packaged into little globules so the image that you're seeing here is basically like a cross-sectional area of the intestinal lumen so we're still in the small intestine these components are packaged into fat globules and this is important now let's take a step back for a second one of the big themes that you're gonna see in this part one of lipid transport is that in order to move dietary fats and their subsequent breakdown lipid products throughout the digestive system we need to optimize surface area so that as we go different enzymes can act accordingly this is the first example of that in the intestinal lumen these components right free fatty acids monoglycerides cholesterol fat soluble vitamins they're gonna be packaged into fat globules right so it's all about efficient surface area big theme in today's video now once you have your fat globules you're gonna pass by the liver now the liver has a duck that goes straight to the small intestine you should know this anatomy from having been in the first two years of medical school now what's the livers role here well the liver is going to secrete something called bile salts and once the bile salts are secreted they're going to act on the fat globules as you see here so bile salts get released from the liver they come to the intestinal lumen through the duct leaving the liver and they act on the fat globules now when they act on the fat globules they're going to further break them down into more optimized surface area again this is all about efficiency you can't process the fat globules like you can smaller lipid products so the bile salts act on the fat globules and convert them into surface optimized fat droplets so these are still droplets they're just smaller and more optimized for further breakdown so now that we have this optimized fat droplet with an adequate surface area to be processed this is where pancreatic lipase comes in so earlier we talked about salivary lipase but now the pancreas comes by and he's got his boxing gloves on right the pancreas is ready to smash these fat droplets and break them down using pancreatic lipase so pancreatic lipase gets secreted from the pancreas and acts on these fat globules now these fat droplets are surface optimized for the pancreatic lipase so look at this necessary step first the bile salts had to take the globules and break them down into surface optimized droplets if that never happened then the pancreatic lipase really wouldn't be as effective breaking down these fat droplets and we would have problems processing dietary fats so the pancreas takes a punch goes for a little uppercut and knocks out these fat droplets with pancreatic lipase now when that happens these fat droplets get converted of course into free fatty acids monoglycerides and cholesterol now I know what you're thinking we already had this we started with free fatty acids glycerides and cholesterol right after we took our first swallow and you're correct right you're absolutely correct but what I'm illustrating here is that lipase breaks down the fat droplets into their key lipid components but salivary lipase couldn't do that fully when you first were biting and swallowing your food right those components went to the intestine for further processing because you needed a stronger lipase which comes out of the pancreas with its boxing gloves on to really smash those fat droplets into the full array of free fatty acids monoglycerides and cholesterol so if we take a big step back there's a few big themes I need to point out first we already talked about optimizing surface area for lipid transport that's the big first idea the second idea is that lipase is from both the saliva and the pancreas but the one in the pancreas is so much stronger than the one in the saliva and think about this when pancreatic lipase accidentally gets on the pancreas right it does Auto digestion and that's how you get pancreatitis imagine if you had that much of a potent lipase in your mouth it would completely digest things in your mouth and you'd have like tongue itis and lips itis whatever I mean I know that sounds stupid but it's the truth so pancreatic lipase is so much stronger than salivary lipase now you have your free fatty acids your monoglycerides and your cholesterol and the next step after we've broken down these fat droplets using pancreatic lipase is to have these free fatty acids monoglycerides and cholesterol combined into a micelle now my cell is really just molecules in a colloidal solution and there's really not much more to know about it but just recognize that in this pathway your key lipid components will package themselves into micelles now this point you've got your micelle sitting there and it's finally time for the micelle to enter the entero site right the functional cell of the intestinal wall so the micelle enters the entero site but technically what it's doing is not entering as much as it is releasing fatty acids and monoglycerides into the entire site so these little orange lines represent fatty acids and monoglycerides and the micelle is literally just dumping them into the entire site they'll diffuse through the entire site wall and now they are finally in the inside of the small intestine so they've been absorbed now this point these free fatty acids and monoglycerides are going to assemble they're smart they know what they're doing they've made it all the way down into the entire site of the liver despite having to face the salivary lipase in the mouth the bile salts released by the liver and the pancreatic lipase released from the pancreas so these guys know what they're doing the free fatty acids and monoglycerides are going to assemble into triglycerides so I've organized them they're in sets of three to represent triglyceride assembly now we've got triglycerides assembled beautifully in the entire site and we're ready for our final step of part one of lipid transport these triglycerides are going to be packaged into Kyllo microns so we finally reached the point of chylomicron formation so this is part one we started with dietary fat it was attempted to be broken down by salivary lipase it was somewhat broken down into free fatty acids monoglycerides and cholesterol it went down the esophagus through the stomach into the small intestine in the small intestine these were organized into globules the liver recognized this and said hold on a second I'm gonna release some bile salts to break these down and to really get that surface area going for future enzymes so the bile salts acted on the globules and made them into surface optimized fat droplets pancreatic lipase was released by the pancreas he came out with his boxing gloves on he said I'm gonna smash these fat droplets because I got to break him down even further into full products such as the full array of free fatty acids monoglycerides and cholesterol once that pancreatic lipase smashed up the rest of what the salivary lipase couldn't do then the free fatty acids monoglycerides and cholesterol organized themselves into micelles which was just a solution that was colloidal in nature with these components in them the micelles dumped the free fatty acids and monoglycerides into the entire site so through the wall of the small intestine and once those components went through the wall they organized themselves into triglycerides once they were in triglycerides the chylomicron was formed and the triglycerides entered the chylomicron so that is part one of lipid transport that's what you need to know so far let's just conclude part one by talking about the big picture so the dietary fats were broken into they're key lipids by lipase in the saliva and then the pancreas these key lipids were shuttled from the opening of the digestive system so from the mouth to the small intestine optimizing surface area as they go key lipids including fat soluble vitamins cholesterol and triglycerides were ultimately packaged into chylomicrons which are going to await further metabolism in the lipid transport biochemical pathway so that concludes part 1 re watch it if you need to understand how we got from the food the fat in the food that you eat to the packaging of the chylomicrons but everything in the next video is going to build upon what we just talked about