Transcript for:
The Circulatory System: Structure

hi everybody and welcome back today we're going to be looking at the circulatory system i'm going to be doing the system in two parts this video is going to focus on the structure of the circulatory system while the second video is going to focus on the processes that take place in the circulatory system now it's important to know the basics of how our circulatory system is structured so that we know how best it can carry out its function because that's one of the golden rules of biology is everything that has a structure has a specific function associated with it now something that maybe you're not aware of is that circulatory systems can come in more than one kind in particular open and closed circulatory systems now the name gives it away an open circulatory system as we can see here on the left hand side of this diagram is in reference to our blood vessels being open so an example that we see in nature is with insects for example like this little grasshopper here essentially what they have is a structure that is similar to a heart blood moves through that pump and as it moves through the blood vessels and approaches the tissues you will notice that the blood vessels are open at the end and that means that the blood actually leaks out of the blood vessel and it goes in and amongst the tissues then on the other side you'll notice that these blood vessels are also open on the other side and the blood somehow enters them and goes back through into the heart now this is an opus open circulatory system and essentially we find this in very small organisms and we're not going to find this in a very big animal and essentially what happens is you are pumping a fluid through the tissues of the organism but the actual blood component the liquid actually leaves the blood vessel it means it actually leaks out now in animals like ourself that doesn't happen our blood is in the closed circulatory system and an example of an animal that also has a closed system is an earthworm closed is very important because what it means is that the blood never leaves any of our blood vessels so that means our blood moves through the heart it goes through our blood vessels and when it approaches the tissues that it wants to move through you will notice that it branches into smaller pieces we're going to learn what those are called soon and you'll notice that they're attached to one another once the blood has moved through these tubes it then leaves that area through a bigger blood vessel back to the heart and it's important to know that a closed system allows for the organism to be bigger and it also means that the blood itself is a little more specialized now that means everybody that technically all of your blood must stay inside a blood vessel at all times it cannot leak out anywhere the only reason why you actually bleed is because you've cut open one of these blood vessels one of these tubes and the blood is is leaking out of it the next important component about knowing our structure of the heart is to focus on one specific function now i'm going to go into a lot more detail on this topic in the next video when i do the processes of the circulatory system but it's important to know that we have a closed circulatory system but we also have what we call a double circulatory system in other words what happens is the heart pumps blood twice around the heart but the destinations are slightly different and so we refer to this as a double circulatory system so we have a closed and double circulatory system present in humans now let's start off with the systemic circulation in other words this is the circulation of the blood to the body and so when we look at the diagram alongside on the left hand side you can actually divide this diagram in half on the right hand side we have the systemic side and so this is how the body uses its blood that it's receiving from the heart fresh oxygenated blood is going to come in from the lungs it's going to enter the heart and it's going to go off into the body delivering high amounts of oxygen and it's going to be low in carbon dioxide as it moves through the tissues it is going to collect more and more carbon dioxide and that then means that the blood is deoxygenated so now what we need to do is we need to take that blood and we need to re-oxygenate it and so that's when we enter the pulmonary circulation pulmonary is another word for lungs and so what happens is the blood is now going to return up to the heart it's going to enter our pulmonary system and it's going to go back to the lungs so this is the pulmonary system on the left and this pulmonary system has low oxygen levels and high carbon dioxide levels it's important for the body to be able to do this because essentially what it's doing is it's pumping the blood twice through your sets of organs the first time the blood moves through the body it's going to have lots of oxygen in it and it's going to deliver that oxygen but as it do does so it collects carbon dioxide that carbon dioxide we have to get rid of it's a waste and so that is when the blood returns back to the heart it is pumped to the lungs and then from the lungs it returns back to the heart where we can start the whole process again sometimes this process is quite confusing because we forget that a portion of this takes place in the lungs and a portion of it takes place in the body but if you envision this diagram here it might help you a little bit better the easiest way to remember the difference between the two is systemic actually means body and pulmonary means lungs in other words the circulation of blood to the body and the circulation of the blood to the heart next on our agenda is familiarizing ourselves with the structure of the components of our circulatory system and we are going to need to know the external structures and we're going to need to know the internal structures of the heart and so what i'm going to do is i'm going to highlight the most important structures because often we get diagrams and text box and notes and we never really know should i know this diagram shouldn't i and it does depend on what grade you are in and what level of high school you're in but generally at the level that we are going to need to know a number of these light labels for tests and exams now i want to point out that the structure of the heart on the outside is actually quite different to what it looks like when you cut it open and you see it on the the internal structure many of us don't actually realize that some structures are sort of drawn more clearly in textbooks than they are actually in real life and some of us actually struggle to identify these things because textbooks don't really look like the real thing and so let's go through the left hand side labels the first label that we see here is the superior vena cava this is a blood vessel it's the largest blood vessel um in terms of veins and it is going to enter the heart sitting just below that is the right atrium now i want to pause here for a moment because it's important to know that the left and the right of this diagram is opposite to your hands and that's because whenever we do anatomy and biology the position of everything is within the body that the organ is coming from in other words we are looking at another person's heart which means it's their right hand side and their left hand side it is not where your right and left hand is now the right atrium is the top chamber of the heart it is where blood is received from the vena cava you then have these coronary arteries now coronary arteries are arteries that are specifically there for the heart now even though blood goes into the heart itself you'd be surprised to find out that the heart actually needs its own blood vessels separate from the bodies and that's because it needs its own in it its own oxygen and energy and so these coronary arteries are specifically there to keep the heart alive and coronary um is associated with heart so when you see coronary think heart the next important component of our heart is the right ventricle this is the lower component of the heart and it's very very muscular i want you to take note of the differences in the consistency and the appearance of the atriums you will notice that this right atrium it sits out on the outside of your heart actually very interesting it's like a little bag it actually sits on top of the heart itself and it's very soft it's not as muscular as the right ventricle and the right ventricle takes up the majority of the side of the this ventricle is quite thick and muscular and it needs to be as it pushes blood out of the heart and into the lungs that then brings me to the other side of our diagram and we're going to look at this very large blood vessel called the aorta it is the largest blood vessel in the body and it carries oxygenated blood to the rest of the body and we're going to look at its functions later on then we have the pulmonary artery now this is just the left one we can't see the right one it's hidden but essentially this is where our blood leaves the heart and goes to the lungs now often arteries and veins are confused with one another and we're going to learn about how we're going to tell the difference very soon but essentially this is the artery that is going to take blood to the lungs we then have the pericardium now they've said here that they've cut it away but if you look very carefully the pericardium is the sort of um almost very thin membranous layer that's sitting on the outside of the heart and it's there to protect the heart against friction because remember the heart moves every single day and if it moves that much it's going to create heat and friction and we want to keep our heart safe so we put it in a membranous bag or sac next we need to look at the left atrium and so the atrium is a little bit hidden here um it's very hidden underneath here but there it is if i make it circle around it the atriums remember sit at the top of the heart in this diagram it looks as though they're on the outside and technically they are sitting atop the heart in other diagrams it looks like the atria or on the inside of the heart but specifically these are the little inflatory chambers that are going to fill with blood before it enters into the bigger chambers below the ventricles then you will see there are coronary arteries now coronary means essentially heart it's referring to the blood system that supplies the heart with its own nutrients because the heart is responsible for giving blood nutrients but it also needs to have its own blood vessels and these are the blood vessels we can see on the surface here then let's go down to the left ventricle the left ventricle is the thickest ventricle out of the two and the reason for the left ventricle being so thick and you'll see that now when we do the internal structure of the heart this is due to the fact that the majority of blood that enters the heart it needs to be pushed up against gravity that then means that the heart needs to contract really hard to push the blood up through your neck to your head to your hands to your feet and to do that you need a really muscular structure and that's what the left ventricle is finally we have the apex of the heart the apex is essentially the pointy tip of our heart and you'll notice that the heart is not perfectly symmetrical it seems to lean to one side and that has to do with making space for other organs in the in the body that surround the heart like the lungs and the liver right moving on to the internal structure of the heart and i know that this diagram is very intimidating there are a lot of labels here but i promise you that some of them you already know we are going to add a few more for the internal structures so we already know the superior vena cava remember this is the largest vein in the body and superior means from above so this is all the blood coming from the top of your body we then have the right pulmonary artery this is the lung artery this is where blood is going to be leaving the heart to go to the lungs to get oxygenated then below that we have a pulmonary valve remember valves are there to prevent backflow so this makes sure that the blood only flows to the lungs and not back into the heart we have pulmonary veins lower and these are our blood vessels that are bringing blood from the lungs back to the heart it's really difficult to see it in this diagram but basically the blood is going into these tubes through the back of the heart and they're going to pop over here on the other side but we'll get to that side soon enough then below that we have the right atrium the right atrium is the area in which blood first flows into we can see that by our arrows this is where the blood comes from the top of the body here is where the blood comes from the lower half of the body now once we move past the right atrium blood is going to flow into the lower chamber of the heart now to do that it needs to go past a valve and we call this the tricuspid valve tri meaning three cuspid because of the shape of the particular valve pieces and essentially this valve opens and closes every time the heart beats and so what happens is blood is going to flow in from the atrium past the valve and now into the right ventricle the right ventricle if we have a little closer look at its structure you will notice that it is quite large and if you look at the surface area and you compare it to its next-door neighbor ventricle it's very large because you've got to collect all the blood from the entire body and you need to push that blood into the lungs as quickly as possible and with the largest volume so that's what's quite large on the inside um but that doesn't mean that the left ventricle doesn't do a good job because it's a little bit smaller i've spoken about why it's smaller but i'm going to recap that soon then we're going to look at the inferior vena cava remember inferior means from below and this is the largest vein in the body and then there is something called papillary muscles papillary muscles essentially work and you may have heard this before if you know anything about the eye papillary muscles are muscles that are attached to our little valve cusps and essentially what they do is they contract and relax and help open the space sitting in between our two chambers and so i'm talking about this space over here i'm just putting a little black line there we need to open and close that space and so these papillary muscles are attached with these filaments these fibers these connective tissue pieces up onto the actual valve itself and they open and close it now if we move along the other side of our diagram what do we need to know well depending on how specific your textbook needs to be this is the carotid artery and the subclavian artery the carotid artery is the one in your neck the subclavian is the one that runs underneath your clavicle bone your collarbone it's a very important artery and then you have what we call the aortic arch and it literally gets that name because it is this big arching blood vessel this entire thing we can refer to as the aorta as well this is just the left pulmonary artery because you need one for each lung a left one and a right one and yet again we see some more pulmonary veins this time this blood is coming from the left lung then sitting on top we have the left atrium here it is okay all of the blood that's sitting in the left atrium this area here that i'm coloring in is coming from the left lung it's full of oxygen now we've gotten rid of the carbon dioxide and we're returning back to the heart now when we go past any of these boundaries remember on the other side we need to move past a valve and sitting between the two um chambers the left atrium and the left ventricle are our mitral valves now that is slightly different in appearance but it does exactly the same job as the tricuspid valve and it opens and closes and prevents backflow we look a little bit lower down and we look at the left ventricle the left ventricle as i said in a previous section of this video is very very thick and muscular and as you can see here if i i color it in if you look at how thick this muscular area is it has to be this thick in order to force blood against the force of gravity it has to really push your blood really hard and the only way to do that is to be very very muscular and this little slight angle is definitely going to help out moving the blood yet again we've got some papillary muscles running down the side and then depending on what your textbook says you will see something called a septum now the septum i'm going to pick a different color now so that we can see the difference here the septum is this piece of muscle that runs down the middle essentially the septum divides the left and right hand side of the heart and it might not be very obvious by looking at the picture but the reason for that separation is the septum needs to keep oxygenated blood separate from deoxygenated blood you have septums in other places in your body think about the septum in your nose it separates your left and right nasal cavity from each other and so the septum in the heart prevents mixing of different levels of oxygen and carbon dioxide blood now last but not least we need to take a cross-section through the heart we need to look at the the layers of the heart starting from the outer layer and slowly working our way in and so that's what we see in this little box at the bottom here we've taken a sliver through the wall of the heart and sitting right on the outside is our pericardium remember the pericardium is a protective layer on the outside of the heart it's like a bag that contains your heart prevents friction sitting just inside of that we are going to be able to see the epicardium this is the just inside layer then we are followed by the myocardium and whenever you see the word mayo i want you to think of muscle because that's what it's referring to this is the most muscular portion of our heart and then the most inner inner layer is called the endocardium and so we have the peri on the outside the epi slightly inside of that the myocardium and then the endocardium right let's move into blood vessels so we have three kinds of blood vessels and um in an exam or test you will most likely be asked to tell the difference between the three you will have to give visual differences and structural differences but you'll also be asked to give functions and so i'm going to start off with looking at the structural differences and i'm going to start off with arteries now arteries are some of your thickest largest blood vessels in the body and they have some very defining qualities one of them being that they have a really really thick layer of muscle so let's run through the labels and compare them to the others first of all we have a thick outer layer of collagen fibers now collagen is extremely strong it is very flexible and what it allows it to do is the artery can flex and move without bursting why does it need to do that you ask well it's because our arteries are moving blood at a really high blood pressure the higher the blood pressure the more likely it is for the blood vessel to rupture or burst so we need to keep it intact sitting just below that is a thick muscle layer with a little bit of elastin in it elastin makes it stretchy and basically what happens is those muscles and this is all the muscle sitting around here sits around the edge of your artery and they actually move now they're smooth muscles so you don't have to think about moving these muscles they do it on their own but it's really important that they do because as they move it facilitates the movement of your blood around your body we then have your endothelium endo remember is a biological word referring to inside layer and so this is the innermost thin layer of cells that is just providing essentially protection and it just makes everything nice and smooth you don't want any blood cells getting caught and snagged along the way then if we look at the central lumen you'll notice that it says it's narrow and if i were to compare it to the vein if we look over to the vein you'll see that the vein is a very wide lumen so in other words what they're saying is if you compare the circumference of the two so if i draw a circle around the artery and then i compare it to the vein we can see that the hole is much bigger the lumen the space is much bigger in the vein and that has to do with the function i'll get to the function soon but let's go over to the vein now if we look at the vein on the outside it's got a very thin outer layer of collagen it doesn't have to be as flexible because blood is not moving through it at such a high pressure it has a thinner layer of muscle it's still there but it's pretty thin i mean if we compare it to the artery and then it also has endothelium any tube is going to be lined with some kind of endothelium and we just spoke about the size of the lumen now how does this structure link to their function well if arteries are there to move blood at high pressure with not always but most of the time oxygen then we're going to need a mechanism that's going to make sure that blood is being pushed to those locations and to do that arteries have narrow lumens so they've got this narrow opening it keeps the blood at a very high pressure it allows blood to be transported more efficiently but for veins on the other hand veins are bringing blood back to the heart um not always just carbon uh deoxygenated blood but most of the time it is and essentially veins are bringing blood back to the heart now that then means that the blood is not really as pressurized as it used to be it's gone through the whole body and it's lost pressure as it's gone along and so the hole is a little bit bigger that's going to allow more blood to flow through it and what's not in this picture is that veins have valves in them so if we did a cross-section through a vein but this time upright there are these little flaps and these flaps are called our valves now this valve is open at the moment and it allows blood to flow past it the moment however blood starts to fall back down or the heart is in between beets what will happen is those little flaps will meet together and close and it will prevent any blood from flowing in the opposite direction so it prevents what we call backflow we can't see it in this image here but they are definitely there now last but not least in our blood vessels are the capillaries these are the thinnest smallest blood vessels some of them are microscopic and they are one cell layer thick now they are literally only made out of endothelium they don't have muscle layers they don't have collagen layers they have no other layers but an endothelium layer which is why they are microscopic why they are so small and the purpose of capillaries is to join arteries to veins it allows for substances to diffuse into their surrounding tissues and it makes it really easy for those substances to move because all they have to do is for example water or nutrients they have to move through one cell layer and that's it they move through that cell the endothelium cell and then they move straight into your tissues i quite like this picture and so i included it here about how arteries and vein structures are very different and this one shows it a bit better side by side and you can see the layers a lot clearer let's start off with the top so first of all the endothelial cells now depending on what kind of level of biology you're doing you might have to call it the tunica intima which is essentially the innermost layer of cells now they both have it they also both have elastin although the amount of elastin in arteries is greater then we have the smooth muscle now this is a defining difference the thickness of the wall of the artery if you look at it over here is far greater in thickness than that we see of our vein and i'll remind you it's to keep blood at a high blood pressure because we want to move the blood around as quickly and smoothly as possible then below that we have the loose fibrous connective tissues so this is the most outer layer this is where we find like that collagen that we spoke about earlier and there might even be epithelial cells on the outside please take note of the scientific names the tunica intima tunica media tunica externa and the serosa depending on what level of biology you're doing you might need to know these names if we look at a little paragraph at the bottom i thought it summarized it very well for us archeries are thick and muscular and they have an elastic wall and they gradually reduce the harsh harsh surge of blood um to a steadier flow what they mean is that as the blood leaves the heart it's quite intense it's quite strong so we're going to make sure that we keep that strength in blood pressure we also don't want to burst any blood vessels in veins their most defining thing is that they have such a large lumen and they have less resistance to the blood flow and we can see how big the lumen is i mean if we have a look here if i take my pen and i circular circle around it there is the width of the artery versus the width of the vein and that width tells us the pressure at which blood is moving this is a high pressure blood this is a low and as we know from physics we are always going to move from a high pressure to a low pressure lastly in terms of structure i included this picture just to show you what it looks like in a micrograph in a lot of tests and exams we get really flustered and confused because we see diagrams of veins and arteries in the heart but we then we see a real image a real micrograph and we are a little bit confused as to what we're looking at because it doesn't look exactly like the diagram so let me point it out we have an example of two micrographs here and we have a vein in either of them now you'll notice the most defining thing about the vein is its irregular shape it doesn't seem to be circular or oval or anything like that particularly this one over here you also notice that you can see this layer of connective tissue on the outside and then not much else and that's because veins are far more flexible they are pretty um able to collapse on themselves it means that they are going to be able to fall on themselves and of course the most defining thing is look at all of this space this is all the lumen in both of them if we look at our arteries on the other hand you can see a very very characteristic thick layer of muscle that sits all the way around and then we also see the smaller lumen sitting on the inside in both of these so let's round up this lesson with the terminology recap we learned that in mammals we used a closed system that means that our blood is contained within blood vessels at all times it doesn't leak out it must stay inside of the heart or inside a blood vessel we also learned that there is double circulation that means the blood returns to the heart twice once to the lungs and then once to the body itself and we call this either the pulmonary circulation which is blood going from the heart to the lungs or systemic which is the blood coming from the heart to the body we have two ventricles which are the lower chambers of the heart and two atria which are the upper chambers of the heart we have the pericardium which is the outer layer of the heart it's the bag that keeps the heart safe we have the epicardium which is the layer of tissue just below it and finally we have the endocardium there is the tricuspid valve that keeps our right hand side of our chambers separate and the mitral valve keeps the left hand chambers of the heart separate we then have arteries which are the thickest blood vessels with the smallest lumens we have veins which are the smaller blood vessels with large lumens and last but not least we have the capillaries these are our joining um blood vessels between an artery and a vein and they transport nutrients and wastes between the blood and the tissues as always if you like this video i hope to see you soon bye