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Blood brain barrier and vasogenic edema

Video transcript

so this is a really really zoomed in schematic view of neurons and their supporting cells in the brain and we know that without enough oxygen let's say that there's a clot right about here and that's reduced the blood flow to this area enough to cause a stroke here without enough oxygen neurons can start to break down as a result of a process called the ischemic cascade so that's obviously not good our neurons breaking down but to sort of add insult to injury here there's actually a few other events that happen after our neurons start breaking down during a stroke so let's look at these these subsequent events so we know that in the initial part of a stroke a few minutes without oxygen will cause our neurons to start breaking down and dying off we know that but later around a few hours later certain components of the blood vessels that serve the area they start to get broken down as well so let me actually zoom in on this blood vessel here let's look at a close-up so you might have heard of the blood-brain barrier the BBB it's essentially this extra layer of security that separates what's inside your blood stream like for example any any drugs or harmful little toxins so the the blood-brain barrier separates what's inside your blood stream from your central nervous system tissue out here and this is to make sure you don't get any weird and not so wonderful infections or any brain injury from things traveling in your bloodstream so what makes up your BBB what makes up your blood-brain barrier well I'll just briefly describe it it's partially composed of endothelial cells which are these neat little cells here that that line the inside of your capillaries so you can see they're really close together here to help prevent unwanted leakages of any little substances then there's the basal lamina which is sort of the endothelial cells underlay and it's pretty thick and it also helps to separate stuff in the blood from stuff in the CNS then there are these tight junctions and I'll draw some of these in here let me just draw in some of these tight junctions so these are little connector proteins that really tightly seal up any space between our endothelial cells and that further restricts any unwanted molecules or substances from getting into the CNS so these tight junctions will prevent them from slipping between your blood vessel cells these endothelial cells and the last component of the blood-brain barrier that I should probably mention are these astrocyte processes here these these astrocyte end-feet and they actually don't have too much of a structural role in the blood-brain barrier but they do provide some nourishment to these endothelial cells so you could say they help maintain the blood-brain barrier in a way so why am I telling you all this why am I telling you this stuff about the blood-brain barrier well because about four to six hours after infarction after you lose your oxygen supply to this part of the brain your blood brain barrier starts to break down and two of the major reasons this happens is because of ischemia in the area and and because of an inflammatory reaction that's going on post stroke so what happens well the combined result is that your endothelial cells start to get a little bit leaky ER and this basal lamina looses its ability to restrict some molecules so it gets a little leaky or two and really importantly these tight junctions stop being true to their name they loosen up a little bit and they also become leaky so you can imagine that this is just a disaster everything is supposed to be nice and tight and now things are pretty out of whack so let's see what ends up happening because of this well proteins and water from within the capillaries within the blood stream because there's often still a tiny bit of flow still happening proteins and waters start to leak out at will so what do you think is going to end up happening now to the brain tissue here well now the extracellular space here is going to get a little bit flooded with proteins and water right so this so-called vasogenic edema vasogenic means originating from blood vessels this vasogenic edema adds to the cytotoxic edema that's already happening in the area and that just worsens the swelling of this part of the brain after stroke and why is this important well for one swollen ischemic brain can't really carry out too many of its functions so we want to minimize the time spent swollen as much as possible and for two it can result in a mass effect which is where the swollen brain area starts to push on or displace surrounding brain tissue unfortunately I'm not referring to the excellent video game series called Mass Effect here I'm referring to a physiological Mass Effect and actually let me show you one of the more severe things that can happen with brain swelling you can develop what is called brain herniation so this is where the brain swelling gets so bad that a bit of brain gets pushed totally out of position so say this bit of brain here gets pushed over toward the other side or say this bit of brain here gets pushed down through this part of your skull where your spinal cord exits your head both of these are known as herniation of brain tissue and they're both often fatal so we don't like brain swelling at all and what sort of timeline are we looking at then for the swelling well the swelling that occurs as a result of this vasogenic edema it tends to get worse over a few days as more water and protein leak out of the blood vessels in the area and it Peaks at roughly 3 to 5 days post stroke and then after that it slowly starts to resolve over the next few weeks as the protein and the water slowly get reabsorbed back into the circulation so this of course is a good thing and it and it brings the cerebral swelling down