Blood Brain Barrier - Structure & Function

right today we are going to talk about blood-brain barrier right now what is blood-brain barrier it is not something like a physical barrier as there in the road and you cannot pass through blood-brain barrier is a basically concept which was originally originated in nineteen about 1882 by experiments of a doctor Paul Eric now what did he do actually he took live animals thank god animals right but even animal rights people will not be happy about it but what did he really do he took them live animals let's suppose here happens to be an animal right and and let's suppose here is the central nervous system of the animal right what did he do that he injected special type of dyes right in there was floor system right vital dyes vital dye to be very exact trypan blue - blue and this molecule of trypan blue now we know that basically it binds with albumin or with the plasma proteins now dr. Paul in red she injected the livid live animal the living animals with vital dies right in their circulatory system and then she tried to study that which organs of the animal are colored by the dye this was a blue color which organs of the animal turned blue what he really found that this injection of the blue dye right ripened blue it colored almost everything in the body except central nervous system all that tissues turned blue right and this blue dye approached all the tissues in the body but it failed to enter into central nervous system so he thought that there must be some sort of barrier between circulatory system and the central nervous system right and this was the origin of the concept of blood-brain barrier this was a very primitive concept very initial concept there what is blood-brain barrier that Paul L make injected basically dies in the vascular system of the living animals and then as these days while protein binding died and then he studied the distribution of the color in different tissues and what did he find that this blue dye was present in all the tissues almost all tissues but failed to enter failed to enter into central nervous system then he thought that it means there is some barrier between the blood and the brain and of course blood and the spinal cord also and later on we discovered similar barrier is present between not only between blood and brain but also present between blood and blood and spinal cord and also between the blood and peripheral nerves even this dye failed to color the internal side of the internal part of the peripheral nerves so truly now we believe this is not only blood-brain barrier even though in common language when doctors discuss the talk only about blood-brain barrier but actually when we are talking about blood-brain barrier we are talking about three things blood and brain barrier and all flow it's understood we are talking about blood and spinal cord barrier and similar barrier is present between the blood and peripheral nerves so blood and nerve barrier am i clear now the question is this ok mr. Paul Alaric made trouble for us that now we have to study this initial discovery but as time went by and there were better techniques to study the you can say this blood-brain barrier to look at it what anatomical exactly and what structurally it is right now we know a lot about it right now we'll go into more advances and we'll talk about that what is exactly blood-brain barrier what is that structure and how that structure work which prevent many substances from the blood to enter into the central nervous system freely central nervous system is like a you know like what should I say one thing you know that central nervous system has lot of neurons and neurons are the master controller and regulator of the body and you don't have very sensitive just like ladies right overly sensitive and neurons like that approach to them should not be thoroughfare is that right this neurons are like ladies very very sensitive and very specific and they like to keep the private environment and they want to keep a very stable environment not whatever fluctuations are going in blood should also come on to their environment in the central nervous system right so let's talk about that here the neuron and this neuron this is the group of neurons here right these are very very sensitive and everything from the blood should not reach there there must be some barrier most of the women believe in barriers right sometimes they put emotional barrier sometimes they put psychological barrier and the same will mean all that put a lot of barriers we'll talk about that but why why there is barrier why should be a barrier that isn't being that even though neurons have to get the nutrition from the blood and neurons have to release their waste product into blood but still all fluctuations and all the drama of blood chemistry should not disturb the biochemical of micro environment of the neurons in central nervous system right for example in the blood hormonal fluctuation occurs very frequently and fast in fasting period hormonal composition is slightly different and postprandial once you have eaten a lot of food your our molar composition in the blood is different if you have done lot of physical activity your hormonal composition in the blood fluctuates you know that about insulin glucagon and other hormones if you are under stress again hormonal fluctuations occur if the big black dog is after you what is surges a lot of norepinephrine in the blood is that right so blood chemistry changes as I told you blood Hartman's change but neurons written here we can say ladies room right these neurons don't love every fluctuation should come there and disturb their special functions right so there must be blood right there so one of the function of the blood-brain barrier is I will tell you later what exactly blood bit barrier is but one of the function of the blood-brain barrier is that it protects the extracellular environment in the neuron in the central nervous system the micro environment of the neuron for biochemical environment of the neuron or extracellular environment of the neuron it protects them from major fluctuations in the blood and not only protect actually it is responsible blood-brain barrier is responsible to keep the neuronal environment stable relatively stable and you rural environment should not be at the mercy of changes in the blood right as I told you that if hormones are fluctuating in peripheral circulation this this should not reflect in the same degree of fluctuations in central nervous system right if there are metabolites in the blood or glucose level in the blood fluctuate a lot when you take food amino acid level in the blood fluctuates a lot and the fasting straight and in the fed state but those fluctuations should not be that much to the central of a system may be to some degree then madam writes in the blood with exercise right the amount goes very high and resting period it becomes less again it should not border the private and discrete world of the neurons so one of the major function is that it is protecting the central nervous system micro environment and which the neurons are working right to keep them into stable milli stable environment and protect central nervous system extracellular environment from the fluctuating hormonal levels metabolites levels in the peripheral blood and even ionic levels right because neurons love to have very stable level of sodium calcium potassium right magnesium chloride bicarbonate protons and there are relatively more fluctuations in the peripheral separation so this is one purpose so we can say blood-brain barrier act as a-- what stabilizer it act as a stabilizer it stabilizes the it stabilizes the internal environment of central nervous system including brain and spinal cord right then it has one more function not only these ladylike neurons love to keep their environment relatively stable and and relatively less fluctuating they also want to be protected there you know ladies need more protection than men's usually even though you come across sometimes very dangerous ladies another function is protection now central nervous system blood-brain barrier protected from toxins endogenous toxins or exogenous toxins right which are produced in the body and diagnose toxins or if you have taken parent early or some toxins you have taken the intestinal system or some other way right there must be mechanism to protect the central nervous system from that so they have one more function not only stabilizations it act as a stabilizer blood-brain barrier it also Atena protectors it protected from the toxins is that right even it protected from the toxic rage of the drugs sometimes you give drugs all drugs don't enter into certain of a system selected drugs do enter right so protected from many many toxic drugs then it protect it from the microbes off it protected from that microbe also specially particulate microbes like bacteria right for bacteria usually it's a little bit resistant to enter into the central nervous system is that right then there is one more function not only its stabilizer of the micro environment in threat another system not only it's protected from the toxic substances and dodging alike bilirubin or exogenous light neurotoxins another thing it's a very good holder hold a holding of what neurotransmitters in central nervous system in different regions you need very special concentrations of neurotransmitters somewhere for proper function of the brain at specific time you need glutamate another area you need may be norepinephrine still some other area you need serotonin and dopamine right and if there was no barrier between the blood and the central nervous system these neurons Willis so these neurotransmitters very very precious chemical substances will drain into blood and flushed away into general circulation and how brain will keep the concentration of such neurons at appropriate level for functional purposes so blood-brain barrier also helps the central nervous system to hold the neurotransmitters within the central of a system so if they are not flushed away through circulation you know how much blood every minute passes through your central nervous system yes your brain looks quite active yes yes you are almost right actually about 15 percent 15 percent of the cardiac output passes from the central nervous system you know cardiac output Julie interesting person to adult is about 5 liter per minute right so you can say about 700 to 800 ml blood you are almost right some 100 to 8 ml blood right and when you are exercising of course cardiac output improves sometimes even more than one little blood passes through the central of a system per minute and if there is no barrier neurotransmitter will be flushed away washed away the reaching will be happy man then are happy woman even know so what are the functions of blood brain barrier I have not yet told you what is blood brain barrier exactly I just told you hypothetically there is something which prevents the free movement of certain substances between the peripheral blood and the shtetl of a system and why man and that something is called blood-brain barrier will discuss with lately what it is but functions of this blood-brain barrier are very important it provides a stable micro and molecular environment in biochemical environment to the neurons it provides protection to the neuron central nervous system and it helped the center Lewis system to hold the neurotransmitters concentration emmaclaire but now we see exactly what is blood-brain barrier right so we'll go to discuss that the structural details of the structure of blood-brain barrier let's suppose he here it happens to be your brain right it is just for teaching purpose it's an out of proportion this diagram but still let's suppose here is your general circulation right and this is the blood vessel which is passing through central nervous system and I will enlarge it so that you can understand it more clearly their blood is going of course from general circulation through you know carotid system and vertebral arterial system to the central nervous system and eventually RT is go into arterioles and then eventually it took a pillories right and then they're drained back from the central nervous system so the venous channel back to the general circulation right so from here it comes out now the concept is that between blood here is the blood and here is what central nervous system extracellular environment between the blood and central of a system there is a barrier and that barrier is here right now we're going to detail what it is right let's both put some neurons here right these are the neurons right they are doing a lot of talking there as you know right so communicating synapse is and all those activities right going on here and it should be very intimate environment and every all the adventure adventurous activity here should not disturb it significantly the system should be so wise that the things which are really needed by the central nervous system should be able to transfer and which I'm not required should not be able to transfer right and here is the barrier now what is this barrier it's not a red line there let me tell you what it is actually blood thin barriers multiple components right first I will tell you a simple component the we should put a comparison between the pillars in other tissues and children in the brain right because these are the endothelial cells of the capillaries which provide the major function of the barrier now let's suppose we put a cappella how many types of capillaries are there there are continuously plays continuously pillories they have fenestrated Capella's fenestrated capillaries and there are sign of soy del capillaries now continuous capillaries are those cable is look here where endothelial cells don't have junctions between them like these are the endothelial cells and there are not between the endothelial area there is not significant gap for the fluids to move so this is continuous Capelli and it is having what is this basal lamina or basement membrane which is also continuous right then they are fenestrated capillaries now what is the difference in fenestrated capillaries fenestrated couple is that the real difference is the real difference in continue stupidly and fenestrated couple layers between the endothelial cell structure the what is the structure that these endothelial cells are - created these endothelial cells here these are feni's pritchett i will explain what is fenestrated right fenestrated now what does fenestration fenestration mean window window look at this wall in this wall let's suppose this wall is then endothelial cell this wall is and those inner cell and if there are round windows here round windows these round windows or holes these holes or pores or round windows are called fenestrations what are they called venice prescience so actually these endothelial cells they are having special type of you can say holes here and through this holes certain things can pass very easily and these are called endothelial windows we can also call them endothelial windows or we can call them and Athenian fenestrations right now these fenestrations in some areas are really true Windows for example in glomerular people days but in most of other fenestrated Kipple is in the window there's a curtain there is a curtain there is a little diaphragm right so both of them are anyway called either there is only window or though the window good curtain in both conditions if any endothelial cell has so many round windows through which substances can easily pass then we say the endothelial cells are fenestrated and if there are cells are and o3 your cells are fenestrated then we say these are fenestrated Kapil is but these continuous Dipple is their endothelial cells don't have these pores or the endothelial window so they don't have the what is this thing called diaphragm with the endothelial windows so we say these are continuous so what is this what is the thing about the continuous or other name is continuous or tight Kapil is right that their endothelial cells do not have fenestrations and Internet or yourself gaps are also not there right classically continuous epithelia on classically continuous capabilities are found in the central nervous system and end on Urim of peripheral nerve I mean brain and the spinal cord and nerves and continuous people these are also found in yes continuous capabilities are also found in just my friend you like to hide your knowledge ah yes you don't like to show off containers to people either at many places but at least we should remember muscles right muscles also have continuous is I mean muscles of is where there are endothelial cell without fenestrations in the muscles and your failure cells are without fenestration but in muscle internal and ethereal gaps are little bit there but in system right these continues to please do not have in Toronto genial gas is that right these are furnace Richard crippled is right then there are sinusoidal in science I really believe that we're endothelial cells have lot of gaps and somewhere there are really deficient wall of the capillaries right classically we can say it isn't present in the liver and discipline right in the liver and the spleen right and there are some particular to senior cells also their macrophages another why I will not go into detail what really wanted to tell you their body has three types of capillaries their continuous is the fenestrated capillaries and there are sinusoidal gap fillers continuous people is they have endothelial cells which are not sanest wretched fenestrated nipple is haven't of seen all cells with multiple and athenian windows called fenestrated capillaries and sign hundreds idle cells are really broken to police right now yes please you have a question here it is continuous here it is a little bit broken here it is really built in patches right now we come to the endothelial cells characteristics of the endothelial cells lining the nipple is of central nervous system right let's come here now if I draw anderson yourself here this is endo seen yourself right and this is one more and within yourself and here is one more endothelial cell now the first time these endothelial cells have a very special thing because this is a private area women like to be behind the curtains and you will occurred on the also the light to splash them more and more so what happened there's special stitches here there's special protein which stretch the what is this inter endothelial gaps these gaps which are between the endothelial cell actually there are no gap they're very tightly stitched right there are special type of threads what are those threads those threads are particularly special proteins called occlusions and Clawdeen's occlude ins cloud ins and 0/1 and many others you don't need to remember all of them but you must remember that in the endothelial cell which are lining that fill is incidental of a system right these endothelial cells are very tightly stretched with each other and substances are not allowed to freely move in between the endothelial cell isn't right and this point where stitching is done this is called there are junctions between the one end of the cell and other things well there is a junction but because Junction is stretched it become a tight Junction so we call them tight junctions the classical most important thing which is present in central nervous system vasculature which act as a blood-brain barrier is that tight junctions is there right this is the main reason why everything from the blood cannot jump into brain and everything from the brain cannot jump into here right so what is the site number one is tight junctions so let me now make this Triple R a little bit larger that there are tight junctions and I will draw the Triple E here right this is metal of a system Triple E and here is your what is this endothelial cell here is an other endothelial cell and so and so forth and here are the stitching done and what are these two genes tight junctions and they are made of special proteins and these proteins are Claudine's and Clawdeen's occluding and Clawdeen's and zero one and some other also right and that is why at least one route through which to usually passage occur is blocked now if I draw here here I am NOT making central of a system for OTA I'm making another type of now in this side this is another capillary from somewhere else in the body I'm comparing to purely from other part of the body with the triple is in the central of the system this comparison now here are number one these stitches are not there if the stitches are not there then what will happen substances will be able to move through this and if substances can move through this right this is called larger molecule or polar molecules polar molecules are those molecules which are highly child horny molecules charged molecules right or the molecules which are you can say water soluble molecule right if someone is very charged dip him into water right so what I'm talking about that these molecules which are larger which are charged which are we say water soluble right these molecules can easily pass to enter endothelial gaps and this is called para cellular root what is this pair a cellular root of exchange between the vascular system and interstitial fluid but in central of a system this para cellular root is effectively blocked is very effectively blocked by tight junctions this is the first most important thing if you don't remember anything about blood-brain barrier just remember one thing then the major reason of this barrier between the blood and the brain is what tied junctions in endothelial cells lining the cerebral is the central nervous system capitalism this is only one but story doesn't finish here you know this is very discrete area extra protections are there actually blood-brain barrier is a sort of neuro protective layer protecting the central nervous system private environment now the other reasons there's another route through which substances pass from the blood extrasolar area and the and that route in other people is is through the cells that is through the cell when substance passes through the cell it is called trance cellular route and this is Paris elderly now cancel the route there are many ways one of the ways that endothelial cell let's suppose this is an endothelial cell transcellular how it can do that it can make a little what is this depression and substance which need to be transferred that will be taken into this pit and then this will move a little in world and now substances in a vesicle in a vesicle and then this vesicle may fuse on the other side and this substance will release out so here it entered there it went out but it passed through a particular system many epithelial cells right which endothelial cells in the many tissues they are having special type of transport from the endothelial cell from one side to other side their special physical or formed on one side right depressions in which proteins or larger molecules which are supposed to be transported at trapped or attached and then this vesicle these tip these pits or depressions they become deeper convert into vesicle and vesicle are transported to the other side of the under seal yourself until vesicles fuse with the cell membrane other side and its content are thrown out and this is called trans site to take vesicular transport what is it called trans cytotec radicular transport is that right and here do you think such kind of trans I trotted vesicular transport should be very effective in these cells no just ask any women this should not be like this that men sit in the what is his drums and pathan so this drum vessel should not be there this is another important reason the blood-brain barrier is there not only because para el celular route is blocked by the junctions but also in central nervous system endothelial cell show very little vesicular transport but other people will show a lot of trans cellular transport to the vesicular system this is a second reason then there is another thing

Channel: Dr. Najeeb Lectures

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Keywords: blood brain barrier, brain, neuroscience, blood–brain barrier, choroid plexus, usmle step 1, usmle, blood supply, dr najeeb lectures, medical school, medicine, medical lectures, neuroanatomy, med school, neuroanatomy lectures, medical courses, neurology, neuroanatomy usmle step 1, neuroanatomy brain, neuroanatomy of the brain, neuro anatomy, armando hasudungan, lecturio, khan academy medicine, medical videos, medical education, blood supply to cns, blood supply to brain

Id: ZrhIbpO5gkg

Length: 29min 33sec (1773 seconds)

Published: Mon Sep 11 2017