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Blood Pressure

109 The Pathophysiology of Hypertension

junio 16, 2018

[VidSitePro id=56 ]when it comes to the way hypertension develops there’s a there are a number of different factors and in order to fully understand the factors we have to do some math because you know math is always fun so let’s talk about cardiac output cardiac output refers to the amount of blood that each ventricle is pumping per minute and in order to calculate cardiac output we need to take two factors into consideration number one the heart rate so that’s the number of beats per minute and we’re going to multiply that by the stroke volume that’s the amount of blood that each ventricle is pumping with each contraction so let’s take some simple numbers here let’s say I have 70 beats per minute so 70 bpm and I multiply that by 70 milliliters I am going to get let’s say 4.9 liter what’s the significance there well when we come to blood pressure let’s do that in a different color let’s use yellow blood pressure can be determined or calculated by taking cardiac output and multiplying that by peripheral resistance we already spoke about this cardiac output but peripheral resistance deals with the amount of resistance to blood flow if there’s an increased resistance to blood flow it’s harder for the blood to get through the vessel that is an increase in peripheral resistance and if you increase any of these two factors if you affect any of these two factors you’re gonna affect blood pressure now usually when we’re dealing with hypertension the main cause of increased blood pressure is going to be your peripheral resistance there’s something that is affecting the ability of the blood to flow through those vessels and that is going to increase your blood pressure and the main reason for that is increased arteriolar arteriolar Vasil constriction and we spoke about this a little bit in the previous video so increased arteriolar vasoconstriction I want you to understand it so let’s draw some arteries here here I have an artery and I’m drawing that artery artery very simply and this layer that I’m showing in white is going to be my endothelial layer and then surrounding that we’re gonna have another layer and that layer is actually going to be a smooth muscle layer and anytime you hear muscle you should think that there’s contraction that’s possible right so if there’s increased sympathetic activity so I’m just going to put simp act increased sympathetic activity the sympathetic nervous system is releasing norepinephrine and epinephrine basically adrenalin that is going to cause constriction or contraction of that smooth muscle layer and as a result what’s gonna happen is the lumen of the arteries it’s gonna get significantly smaller so you see you have less space here now what does that do is it if you have two tubes and one is wider and the other is narrower which one is going to be easier for water to flow through of course the the wider one because there’s more space and that’s the same way it is with the arteries if the arteries are narrower you’re going to have more resistance to flow increase peripheral resistance and as a result that’s going to cause an increase in blood pressure there are other factors that come into play and to show that let’s get rid of this stuff if there’s increased peripheral resistance that is going to make it harder for blood to flow to the destinations that it needs to go to and as a result of that one of the places we’re going to see that effect is that there’s going to be decreased blood flow to the kidneys should I try to draw kidney here sure why not my drawing is not the best but let’s say that’s a kidney let’s just imagine that that’s a kidney as a result of that decreased blood flow to the kidney the kidney is going to release renin and that renin is going to have a number of effects two main effects and what I’m describing here is going to be called the renin-angiotensin angiotensin system or mechanism and we’re going to have two different pathways that are going to be at play here pathway number one is going to be that Renan is going to cause angiotensinogen and geo ten and I’m going to do it in two lines so that it doesn’t take up too much space tense in Ojin and your Chen angiotensinogen I can’t speak to be converted into angiotensin one so let’s just put ang one angiotensinogen is going to be a protein an inactive protein that is produced in the liver and that then gets converted to angiotensin one when the kidney releases renin then there’s an enzyme that is going to convert angiotensin 1 into angiotensin 2 and the name of that enzyme let’s do that in orange is going to be a c e and that stands for angiotensin converting enzyme it converts angiotensin II into angiotensin 2 and the significance here is that angiotensin 2 is going to be the most potent Veysel constrictor vasoconstrictor in the body and of course with increased vasoconstriction what is that going to affect that is going to affect peripheral resistance that’s going to cause an increase in peripheral resistance this should sound familiar I’m going to draw a square around that because that is very significant renin also has another effect and we’re going to do that in a cyan color and that is it’s going to cause the release of aldosterone aldosterone and the significance with aldosterone is what that is going to do is it’s going to cause an increase in sodium ion reabsorption and as a result of that also h2o reabsorption so what’s going to happen is it’s going to cause an increase in sodium ion reabsorption and the water is going to follow that sodium ion this is all happening in the kidney and one of the main functions of the kidney is to filter the blood and to produce urine so we’re getting rid of waste and regulating the amount of water that leaves the body is very important in maintaining fluid balance in the body okay so if your reabsorbing more water into the body that is going to cause an increase in blood volume so the volume of the blood is going to increase and as a result of that if you have more blood and increased blood volume when the heart contracts it’s going to be sending more blood and yes you guessed it that is gonna cause an increase in cardiac output these both should look very familiar to you right now and in red I am going to show you that that is going to these two factors are going to result in what an increase in blood pressure how do we know that because we looked at that handy dandy formula that was BP is equal to you should be reciting this with me see-oh times P R and because of that decrease in blood flow and that renin release we’re activating these two different pathways that are going to result in increased output and increased peripheral resistance which in essence increases your blood pressure now here’s the problem if you’re increasing blood pressure even more that can cause even more damage to the blood vessels and as a result of that we can draw an arrow that’s going right back here because if we’re damaging the blood vessels we also have sympathetic activity that’s happening that is going to cause a reduction in blood flow to the kidney and you can see that this is a cycle and this is why hypertension is such a terrible thing because it kind of feeds on itself and makes itself worse and in order to stop it we need to stop this at one of these points depending on how bad it is so there are a number of places that we can stop this process and that’s exactly what we want to do

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