So welcome back. We're going to be talking about the cardiovascular system. So this is the system that's going to circulate all the oxygen that the respiratory system will have brought into the body and circulate the nutrients that the digestive system would have absorbed, and of course, deliver the waste to the renal system so that the body can get rid of it later on. So all those systems will be discussed a little bit later but let's just concentrate what the cardiovascular system basically really is. It's basically a pump with a bunch of pipes. So the pump is basically a heart that is going to circulate all of the fluids to the right places of the body. Really, it's basically designed to pump the blood to the major organs and, of course, to the muscle because the muscle requires the nutrients and oxygen so that you can do your daily tasks. So the heart is made up of four chambers; the right atrium, the left atrium, which are the two upper chambers, and the two lower chambers which are known as the right ventricle and the left ventricle. So those of you are thinking, "How much sleep do I need?" Most people say, you need about 8-9 hours, maybe when you're younger you need a little bit more. So and then other people will tell you, "You only need 4.5-5 hours." What's the difference? It's because they're not telling you what the reference point is. Your brain really only cares about five hours of sleep. So in other words, you can go to sleep for five hours, your brain is very happy with it. Who's unhappy? It is your heart. The heart requires about eight hours of rest because it is doing a very difficult job. What's this job? To pump against gravity. So even though you don't think about gravity of being very strong, we don't really think about it that much because most people on earth we don't really care because it's always surrounding us but the fluid has to go against gravity. So who is always working very hard? Think about it how fast does or how many times does your heart pump in a minute? 70 beats per minute they say. Says that one per second or is that even faster than a second, of course, here you know that a minute has 60 seconds so therefore these guys are pumping faster than one per second. So in other words, they're doing a lot of work. So the ventricles are constantly doing this against gravity, it gets tiring. They require a lot of oxygen, of course, they require a lot of nutrients, when the nutrients and the oxygen does not arrive at the heart this is the reason why you really die very quickly when those two things run out. The right ventricle and the left ventricle is going to pump to the two different parts of the body. So basically, when you're thinking about the heart, it is to circulations that it has to work with; one to the pulmonary system or to your lungs and the other one to the rest of the body which includes your brain, your muscles, and your vital organs. So the piping is rather simple, you go from an artery to the parts of the body and then it comes back as a vein. So if you can't remember this they always tell you in elementary school, A for away from the heart. So an artery takes blood away from the heart while veins bring blood back to the heart. So what's the difference between an artery and a vein? It is how thick the middle part or the musculature of the artery or the vessel really is. The artery being the much larger of the vasculature can really contract. So when you're thinking about contraction, most of the contraction is done by the heart but about 20-30 percent of your movement of your blood is done by the order itself. So you can probably hear your heart pumping when you put a stethoscope on or even just placing your ear on top of somebody's heart, you can hear the rhythmic contractions but you can also feel the contraction of your artery. So this is the reason why you put your hand over your radius or the top portion of your forearm and you can feel the contraction. That is not due to the contraction of the heart, what you're feeling, the pulse, is actually a contraction of an artery. It is due to the musculature that surrounds that vessel called the artery. So an artery and a vein is very similarly in anatomy wise but the artery has very large muscles to help it contract. So the vein, because it does not have a lot of oxygen traveling through it, cannot support the muscles so therefore the muscles start to become thinner. When you have less muscles around the veins, can you contract it as much? No, as you already have understood. So these veins require special help. What are the special helpers in the vein that helps it to pump the blood back to the heart? It is valves, and valves are all located in an anti-gravity configuration. So in other words from your legs they are all pointed towards the heart, your arms, they're all pointed towards the heart when your arms are resting straight down, hence the reason why when you lift up your arm the veins, now the valves are pointing straight to the heart, and therefore it can drain the veins rather fast and this is the reason why you cannot hold your arm up for a long period of time. So all of these concepts, you need to bring back the blood back to the heart so that it can circulate again and send it to the lungs, and then once you get the oxygen from the lungs, it will come back to the heart and then it will be sent to the rest of the body and the body will bring back carbon dioxide, the waste, and then send it back to the lungs so that it can be expelled. So what were the two chief waste products that our body makes constantly? It is carbon dioxide and water and this is always gotten rid of by our breathing, so every time we exhale we are getting rid of our chief waste products, carbon dioxide and water. So you have a chart that shows you your major arteries and veins that you'll find in your body. You have your major arms and your legs and they form parallel circuits that brings it back. So in other words, from the heart you go through an artery, you go through a capillary where you have interchanged between ions, oxygen, gases, waste, and it comes back as a vein and then comes back to the heart again. So this is why it's called the closed-loop system. So the cardiovascular system is considered a closed system. Later on, we'll talk about the lymphatic system, which is an open system. So in that case, you don't have a tube that is joined together to the heart, you have a tube that comes from your periphery and it empties into your heart, so therefore it is a one-way system and it's an open circuit. So what is the lymphatic systems going to do? It's going to bring back the excess fluids that the cardiovascular system has released into the periphery and bring it back. So when the lymphatic system is not functioning very well, what happens to your peripheral, parts of your body like your hands or your feet? They become bloated or you have fat ankles. It is all because the lymphatic system has failed to bring back the fluid back to the heart and once it's brought back to the heart, the heart will be able to send it back out again but, in this case, instead of having just carbon dioxide as the lymphatic system would have brought back or the vein system would have brought back, it will have oxygen-rich supply that is going back out so that the body and the cells will thrive from it. So we said before, two systems exist, one for the pulmonary system, and one for the systemic system. So the pulmonary system, it is done by the right side of the heart. So all the blood will enter the right side of the heart and the right side of the heart will send all that blood to the pulmonary system. The pulmonary system will return the blood back to the left side of the heart, and the left side of the heart will send it to the rest of the body or the systemic circulation. So what are some of the major parts of the systemic circulation? It is to your liver, it is to your stomach or your digestive tract, it is to your renal system, and the rest of the body, the the legs and the appendages. So all of these things, you can measure how well your heart is doing, and we call this cardiac output. We can measure this easily by multiplying the rate of the heart or the heart rate by the volume that the heart is actually delivering or the stroke volume. Having a good cardiac output tells us our heart is in good shape or in bad shape. So the heart basically is a cell functioning organ. How does it beat? It uses action potentials, and it spreads the voltage around the muscles. So again, action potential is very important. It makes heart muscles work, it may skeletal muscles work, it makes smooth muscles work. It is all done by an action potential. The action potential circuit of the heart is called the electrical conductance of the heart, or the heart conducting system. It is made up of leader cells or nodal cells. They are cells that are not really nerve and they're not really muscle, there's something in between or hybridized cell. They exist in two places. One is found in the right atrium sinus, and hence there known as the sinoatrial node. The other one is between the atrium and the ventricle, so therefore it's called the atrioventricular node. The atrioventricular node has a long process that comes off of it. So in other words, many cells link themselves up together to form what's called the atrioventricular bundle, or the bundle of His. Then the bundle will be separated into two fiber tracks, or the bundle branches. The bundle branches will come to the point of the heart, which is known as the apex, and then it will climb back up the walls of the ventricle. When the fibers climb back up the walls of the ventricle, it is known as the Purkinje fibers, giving homage to the person, who has discovered it, the scientist by the name of Purkinje. So what is the heart really do? With all of those action potentials generated with the leader cells, it is going to rhythmically contract the heart, making the atria contract first, and then followed by the middle portion because that's where the, if you remember, the diagram, the bundle of His and the bundle branches, and the Purkinje fibers come straight down the septum, and then it starts to climb up again. So in other words, when you have a ventricular contraction, it's not a very simple, just squeezing, the septum will shrink first, and then you have a collapsing of the walls, and that's when you have the most efficient way of delivering fluid in an anti-gravity system without damaging any of the valves. So the blood pressure and the muscle, when the heart is contracting, it will cause pressure. When the heart is at rest, this base minimal pressure is called the diastolic pressure. When the ventricle is fully contracted, the load onto an artery is at its highest or the force of contraction is at the highest, and we call this the systolic pressure. Why is systolic pressure or diastolic pressure very important? It's to tell you how the blood vessels will be doing. So we had an artery and we had a vein, and we had capillaries. So what makes them different? An artery has three layers. It has a connective tissue outside, usually made of elastin, so they can stretch. The middle layer is made up of muscles, that we talked about the smooth muscles that thickens in arteries and is very thin in a vein. The inner lining of the artery, epithelia, basic simple epithelia that we talked about before, like the simple squamous epithelial, which is a very thin layer. So it's made up of three layers. So when an artery exists, it has very large muscles that can hold onto the volume. So when an artery contracts, the muscle helps from expanding too much. So when you don't have that muscle or the muscular layer, when there's too much pressure, what can happen? The muscle will expand too far too fast, and therefore the connective tissue that puts the muscles together might rip a little. When it rips a little, and you have weakness of that wall, we call it an aneurysm. So you heard of many aneurysms or you might have heard of aneurysm, in fact you might have a ballplayer who is perfectly fine for one second or two, and then he went out for a long pass and then he caught a pass, and then might have just collapsed at the end goal. Why did this happen? Because he did not possibly understood that he had an aneurysm, and it basically burst, and blood was bleeding internally for him. These are very dangerous concepts. So you have to make sure that you don't have too much pressure at a pipe or the vessel, so that these things do not exist. So systolic pressure is the most amount of force that the cardiovascular system will adhere to or feel. So therefore, if you have too much systolic pressure, it's very dangerous. Of course, the diastolic pressure is supposed to be where the heart is relaxing. But sometimes when you're under a lot of stress, the diastolic pressure would be the same as the systolic pressure or in other words, it just ratcheted up. So in other words, you should have been at 120 millimeters of mercury over 80 millimeters mercury but you might be sitting at a 150 millimeters of mercury because you became hypertensive because of the stress. But then the diastolic rate might be at a 120 millimeters per mercury, which means that you are always constantly putting too much pressure on these pipes. When you put too much pressure on these pipes, they will burst open, and this is the problem why blood pressure kills.
