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Current time:0:00Total duration:14:09

General overview of the RAAS system: Cells and hormones

Video transcript

the body has a really really cool way of controlling blood pressure and you'll hear about this wrath system and wrath stands for renin-angiotensin are a a aldosterone system so let's go through this wrath system kind of as an overview just looking at where things start from and where things go in terms of cells and hormones so those are the two things I want to try to distinguish between so this wrath system RAAS it begins with a set of cells so I'm going to draw all of my cells as little blue houses like that and the hormones that they release are going to be orange messengers so I'm going to draw a little messenger this would be my little person and so the person is the hormone and the blue house is the cell now the the key cell in just a-- in the wrath system is the juxtaglomerular cells sorry so j.g cell and these juxtaglomerular cells are actually in the kidney but they're in a specific location actually in blood vessels and if you look closely these JG cells are nothing more than very special smooth muscle cells so if you look in the blood vessel they're actually just like smooth muscle cells I'm going to write smooth muscle just to remind you this is just a reminder of where they are and of course these are in the kidney so here's my little kidney I may not look like a kidney but that's what it's supposed to be so the juxtaglomerular cells are releasing a hormone called renin and when would they do that well renin is eventually we'll see when eventually going to help us raise blood pressure so if the juxtaglomerular cells if these little guys notice that blood pressure is low that would be a trigger for releasing rennet that's the first trigger so low blood pressure very good now that's not the only trigger there are actually three triggers in total so let me write out two and three and let's go through what they are so the second trigger is a neighboring cell so this neighboring cell is actually a sympathetic nerve cell and we know that sympathetic nerve cells nerve cells they fire whenever some something big is going on so for example let's say you're running away from a bear or let's say you're trying to win a fight or let's say you're in a car accident and you're bleeding any sort of major major stressor is going to cause these nerve cells to start firing and when they fire that JG cell starts releasing running so the second trigger would be sympathetics I'll just write sympathetics or maybe sympathetic nerves now if these are your neighboring cells these little sympathetic nerve cells because they literally end right on the JG cells then a little ways away still in the kidney of course but still a little ways away not touching the JG cells would be the macula densa cells macula densa cells now stay with me for this these macula densa cells are also in the kidney and actually they're specifically there in the distal tubules of the nephron so remember the distal convoluted tubules there there there and there they're interesting ability is the ability to sense sodium and when they when you have low blood pressure not a lot of blood is moving through that glomerulus and so not a lot of fluid is moving through the nephron as a result and a lot of the salt is being reabsorbed so by the time it gets to the distal convoluted tubules the macula densa cells they're kind of tasting or sensing the the fluid that goes by and they say you know there's not a lot of salt here and they put two and two together and they realize that the reason there's not a lot of salt is that blood pressure is low so when they don't sense much salt they say hey JG sells wake up do something about this raise blood pressure for us and so they send a message over in the form of prostaglandins so prostaglandins are kind of local messengers unlike renin which kind of a long distance messenger prostaglandins act locally and actually lots and lots of cells in our body use prostaglandins to send local messages so that's what they do so the third trigger just to summarize it would be low salt in the distal and the distal convoluted tubule and you know specifically that it's the macula densa cells that pick up on this convoluted tubule okay so these are the three major triggers for renin release and now this is all happening in the kidney right that's that's where all this action is occurring but you know there are other organs involved in blood pressure control as well and the one that is next on our list is the liver cell so liver cells now actually here we go little house four cells are also making a hormone of their own and it's going to meet up with renin in a second and it's called angiotensinogen angiotensinogen and angiotensinogen is kind of like a sleepwalker it's sure to zoom in on its face and be asleep and so I'm going to draw it that way it's there and it's moving around the body but it's not active and that's the key thing it's not active but it meets Renan and Renan literally chops off a big hunk of angiotensinogen and if that doesn't wake you up I don't know what would so angiotensin engine becomes angiotensin 1 angiotensin 1 after meeting Lenin so Renan is an enzyme that cuts a big chunk of this angiotensinogen protein away and angiotensin 1 is the result and if you're zoom in on this guy's face it would be awake maybe even a little smile so angiotensin 1 now floats through blood vessels and of course blood vessels have cells lining them so let's draw a little house so little cells and these are the endothelial cells these are the cells that are lining the blood vessel on the inside and classically we used to think that this is almost always happening in the lungs but more and more realizing that it definitely does happen in the lungs but it's in other places as well other vessels as well and so endothelial cells in a number of parts of our body including the lungs are able to convert angiotensin 1 into angiotensin 2 so angiotensin 2 is formed and this is also of course a hormone so I'll draw it as a little person and angiotensin 2 is happy as a clam because angiotensin 2 has lots of activity very very active hormone does all sorts of things I'm going to draw them in for you now so angiotensin 2 will go out to a number of different places I'm going to draw for arrowheads here one two and two in the middle here three let's do four and so it goes to four places and four different cell types are affected by angiotensin 2 now keep in mind at the beginning of all this we're trying to raise blood pressure so just keep that thought in your head so for different cell types are affected and here is a fourth so the so the first one over here is smooth muscle cells in the blood vessels so smooth muscle cells and this is blood vessels all over the body not just in the kidney well this is smooth muscle cells all over the body are going to contract they're going to constrict down and they're going to cause increased resistance because you remember that as the blood vessels constrict vasoconstrict that will increase resistance okay so that's one effect now in a different cell type altogether and the kidney cells the kidney cells you actually have the ability the injured ensign to actually makes these kidney cells hold on to more water so you have more volume it actually helps the kidney hold on to more water and more volume think about in terms of stroke volume is going to increase stroke volume so you've got increased resistance and now increased stroke volume so those are two cell types that angiotensin 2 will act on it also acts on a couple of glands so I'm going to try to draw for you the pituitary gland and this pituitary gland is sitting at the base of the brain and this gland is called that because it secretes hormones as well so it's actually sending off messengers as well so here's a little hormone again in orange remember all our hormones are in orange and this one is called ADH ADH antidiuretic hormone and that ADH does some of the same stuff at the end of the day that angiotensin 2 will do in that it will increase resistance of blood vessels and it will actually also increase volume by making the kidney hold on to more water now the fourth cell type is going to be the adrenal gland so the adrenal gland is here and this adrenal is called add renal because it's sitting on top of the on top of the the kidney which is the adrenal this adrenal gland is also making a hormone because it's a gland and that hormone is going to act right there this is your little messenger and this is called aldosterone aldosterone so you've got aldosterone and ADH that are also acting on some of the same cells and and I should rephrase that not exactly the same cells but the same organs as the angiotensin 2 so here aldosterone is going to act on kidney cells to increase volume and ADH is going to act on as I said before the kidney and smooth muscle so let me scroll up let me scroll up and show you now from the top some interesting things I want to point out so we've got at the very top all of the action you'll remember started in our kidneys right so started in the kidney with the macula densa cell and our JG cell and even our nerve endings or in the kidneys and one of the key target organs down here is of course the kidney so things are starting in the kidney and also ending in the kidney now you'll say well what about this move muscle cell isn't that all over the body and you're absolutely right it does also affect smooth muscle in other parts of the body but I just want to point out the fact that the kidney is a major player in this game now that's one point the other point is that when people talk about the renin-angiotensin-aldosterone system they're talking about certain pathways and they're specifically talking about for example this arrow right here this hormone obviously they're talking about this angiotensinogen and they're talk about angiotensin 1 and they're also referring to angiotensin 2 in all of its targets so they're going to talk about angiotensin 2 affecting the smooth muscle and the two glands the pituitary as well as the adrenal gland and its effect on the kidney so they're really referring to all of those things so they want to make sure you remember that that it's affecting for at least four target cell types and finally that aldosterone down here is it has a huge effect on the kidney as well so these are the important points to take away from this overview that there are many different hormones involved and I've tried to keep them color-coded all in orange to make sure we keep track of them and the fact that the kidney is a major player in blood pressure control