Cardiovascular System 2, Heart, Blood flow through the heart

what we want to do now is look at the blood flow through the heart in a little more detail now if you've watched the previous video clip you'll know that the blood is returning from the lungs via these pulmonary veins and we've drawn this in red because this blood is fully oxygenated and it's going through the left side of the heart we've also drawn on the partly deoxygenated blood returning from the systemic venous circulation via the superior and inferior vena cava going through the right side of the heart and going off to the lungs in order to be oxygenated now this bit of the heart at the bottom here where it goes a bit pointed confusingly that's called the apex so the apex is at the bottom and this bit here is the base of the heart the base is flatter and the apex is more pointed and an immediate thing to realize is that the atria and the ventricles are contracting because of the contractile myocardium and both atria will contract at the same time and they will contract down the way like that so the blood is going to return let's take the example from the pulmonary veins the Bloods returning in the pulmonary veins and while the ventricles are relaxed the blood can just go straight through this valve here because this valve opens down the way and we can maybe illustrate that with a pen so here we have the blood in the atria these valves open down the way and that just allows the blood to go through so the blood can go from the atria to the ventricles because that valve opens down the way now just before it's time for the when the next cardiac cycle is about to begin this is going to be some of this blood that's returning in the atria here and what we want to do or what the heart wants to do is to fill up this ventricle so at the start of the cardiac cycle the atria are going to contract forcibly and that means that more of the blood which happens to be in the atria at the time which has just returned from the lungs is going to be forced through that valve filling up the left ventricle so maybe approximately 2/3 of the blood that is coming back from the lungs just go straight through and then the last third of the blood that gets into the ventricle is from the atria contracting forcing the blood from the atria into the ventricle filling the ventricle pub and that effect is called the atrial kick and it increases the efficiency of the heart now the next thing that happens is the ventricle starts contracting and that ventricular wall has to go in the way like that and at the same time the muscle in the septum contracts and it moves up the way so that wall moves in the bottom part is going to move up and at the same time the heart twisted a little bit as well that's called cardiac twist but the effect of this inward upward and twisting movement means that the volume of the left ventricle is going to be quickly decreased when you decrease the volume that's going to increase the pressure of the blood in the left ventricle and when the pressure increases because this atrial ventricular mitral valve is pointing down the way when the pressure increases in the ventricles below that's going to slam that valve shut so it's going to open down the way then slam shut so an atrial ventricular valve is going to move like this and can't move up the way it can't open up into the atria because the tendinous cords and the papillary muscles stop it so it will passively move down the ventricle will contract the increase in the pressure of the blood and the ventricle will slam that Valve shut and that will prevent regurgitation into the atria which would be a pathological situation but as the teshon here increases can you see that this valve the aortic semilunar valve is going to open up the way like that so while the atrioventricular valves open down the way the arterial valves open up the way like that so as that valve opens that's going to allow the blood to go from the ventricle up into the aorta but when that when the ventricles finish contracting and the ventricular wall relaxes some of this blood is going to try and come back and we don't want the blood to go from the aorta back into the ventricle so what will happen then is the ala or tick semilunar valve will shut and it won't do that that would be a again that will be a regurgitation situation so the atrioventricular valves do this and the semilunar valves do this the valves are not actively contracting they're opening closing as a result of pressure changes developed by the contraction of the heart and the venous return of the blood in the same situation on the other side the blood is going to come from the superior inferior vena cava into the atrium most of it will just flow through but then for the next cardiac cycle the atria will contract generating the atrial kick pushing blood through to here at higher pressure the right ventricle will contract as the right ventricle contracts that will decrease the volume which will increase the pressure which will slam shut the tricuspid atrioventricular valve so that opening that way then it will slam shut that way and at the same time the increase in pressure in the right ventricle is going to open the pulmonary arterial valve the Palmer central unna valve which of course opens up the way allowing the blood to go up at the end of contraction if this blood tries to get back down again that flow of blood is going to shut the pulmonary arterial semilunar valve so we have a one-way flow of blood from the veins to the atria to the ventricles out into the arteries that's what valves are they ensure one-way flow both atria are contracting at the same time both ventricles contracting at the same time so that means when the ventricles contract that's going to shut to the mitral valve and the tricuspid valve essentially at the same time now does it make a noise when you open a door well it shouldn't that it's got creaky hinges if you slam it shut then that makes a noise so it's the slamming shut of the door that makes the noise and it's the same situation here when the ventricles contract that's going to slam shut the mitral and the tricuspid valve and when those valves slam shut like that they make a noise and that noise is called a lub so they make a noise called a lub that is the slamming shut of the atrioventricular valves and then the ventricles are going to contract the blood is going to go up into the large arteries and the blood is going to try and get back down from the arteries back into the ventricles and as that blood tries to get back down that's going to shut the arterial semilunar valves and again when those valves shut they're going to slam shut and make a noise and that noise we normally refer to as a dub so atrioventricular valves are going to go dub lub lub but the arterial semilunar valves are going to go dub dub dub dub so collectively what we have when you listen with your stethoscope is a lub dub and then a pause so the sound of a normal heart we would get the dub lub dub lub dub lub dub but don't take my word for it try out on one of your friends as soon as possible so there we have the basic flow of blood through the heart controlled by the valves ensuring one-way flow circulation through this most incredible of pumps the heart

Channel: Dr. John Campbell

Views: 921,507

Keywords: heart, blood flow, cardiovascualr system

Id: sh5DZU2eVxk

Length: 9min 52sec (592 seconds)

Published: Fri Jun 26 2015