To the Heart of the Matter: The Cardiovascular System in ASL and English with Paul Buttenhoff and Kendall Kail Interpretations by Patty McCutcheon Produced by Todd Tourville

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The Cardiovascular System - Technical Lecture

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Paul Buttenhoff in English

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English Transcript

This lecture will focus on the cardiovascular system, one of twelve or so major organ systems in your body. The cardiovascular system is the primary transportation system in your body. When glucose travels around your body from your liver to your toe, for example, it is your cardiovascular system that is responsible. When oxygen travels from your heart to your brain, it is the cardiovascular system that’s responsible for that transport also. The two basic components of the cardiovascular system are the heart, which is the centralized pump and then miles and miles of hollow tubes that carry blood, that we technically know as blood vessels, or veins, arteries, capillaries, and several different types. Today, we are going to focus primarily on the heart.

In order to understand the heart, we are going to have to understand first of all what the heart is made of. All organs in the body are made of small living units called cells. The heart is completely made up of living cells known as cardiac muscle cells. These cells are unique because they are found no where else in the body. Cardiac muscle cells, like most muscle cells, have the ability to shorten or contract. There are however, several properties that make cardiac muscles cells relatively unique. First of all, cardiovascular muscles cells are said to be autorhythmic. That’s a special property that means they can generate their own action potential, or own electrical activity without relying on the brain or the spinal cord. For example, if a heart is removed during a heart transplant operation, the heart will continue to beat after all connections are severed. We’ll talk about this autorhythmicity in a moment. Cardiovascular cells are also able to stimulate adjacent cells. For example, to activate all of the cells in the heart, all of the millions of cells in the heart, its only necessary to stimulate two or three of them. These waves of action potential, or waves of electrical current, can travel to adjacent cells.

The heart is a round organ, roughly the size of a small grapefruit, and it contains four hollow spaces, internally. The walls of the heart are made of these cardiovascular muscle cells, but the internal chambers are known as atria or ventricles. The heart has a couple of different primary functions. It will receive blood that’s deoxygenated, that’s flowing from the brain for example, or from the pancreas, or from your little toe. The heart will then send that blood up to your lungs so it can saturate itself with oxygen. Blood will return to the heart, and last but not least, the heart has the responsibility of sending this oxygenated blood out to every single tissue in the body.

Deoxygenated blood enters the right side of the heart in the small upper chamber, called the right atrium, and you can see that in the page that I’ve handed out to you. Deoxygenated blood flows from the right atrium, down through a small one way valve into the right ventricle. Throughout the heart, we are going to find these little one way stop and go systems that are essential for ensuring that blood travels from one direction. Deoxygenated blood then flows from the larger right ventricle, up to the lungs, through a pulmonary trunk, which is essentially an artery, because it carries blood away from the body, but it’s unlike most arteries because it carries deoxygenated, or bad blood. The pulmonary artery… arteries, excuse me, pulmonary artery will carry blood up to the lungs, where the blood will circulate in lung tissue and become saturated with oxygen. This is also called the pulmonary loop, as opposed to a systemic loop, which would be any other organ or tissue in the body.

After blood spends a few moments in the lungs, it returns to the heart, except on the left side, and it enters a small upper left atrium. The blood is then returned through structures called veins, although these are going to be unlike other veins that usually carry poor blood, the blood then returns to the left atrium from the lungs, and is the absolute most oxygen rich blood you have in your body. From the smaller right atrium, blood is going to be pumped, down through another valve, into the biggest chamber of your heart, known as the left ventricle. The small valve that protects and ensures that bloods flows down, from the atrium into the ventricle, is also know as the bicuspid, or mitral valve. Often times, because this valve is experiencing great pressure, this valve will give way and blood can actually flow in the opposite direction, which is relatively dangerous is some cases, but is also know as a heart murmur. Once oxygenated blood is in the left atrium, it flows down once again through the bicuspid valve into the left ventricle.

The left ventricle has the most muscle of any of the chambers. It’s got the responsibility of getting blood out to the rest of the body. All of your 5 trillion cells absolutely rely on the ability of this chamber to contract. When the left ventricle contracts, it forces blood up and out through a small valve, into the largest blood vessel in your body, known as the aorta. The aorta is then going to send branches up to your brain. The aorta will then send branches down through your thoracic cavity, and eventually down into your legs. The aorta is the largest artery in your body, and it contains oxygenated blood. So, we’ve got four chambers that work together to push blood into a specific fashion.

What we really have to worry about now, how we regulate those chambers, if the atrium and the ventricle decided to contract independently, blood would not flow effectively, and we would end up with a big mess. The cells in the heart are controlled by the cardiac conduction system. The cardiac conduction system consists of several specialized cardiac muscle cells that function only to carry information. These cells, unlike true cardiac muscle cells, do not contract. In a sense, they are modified nerves, or modified circuits. The primary controller of heart function will be called the sinoatrial node. The sinoatrial node is also sometimes called the pacemaker and is found in the upper corner of the atrium. It’s going to be in the upper right corner of your heart. About 100 times per minute, special autorhythmic cells, in the sinoatrial node generate impulses. Every time one of these impulses is generated, the impulse is carried through the heart by all of the cells. If you remember, we said that the cardiac muscles cells have that property, of being able to stimulate adjacent cells. When the sinoatrial node fires, or generates an impulse, because it’s closest to the atria, both atria contract almost simultaneously. The two top chambers of the heart work as a unit. When the right atrium contracts, it forces blood into the right ventricle. When the left atrium contracts, it forces blood into the left ventricle. So simultaneously, blood is flowing from the top of the heart into the bottom of the heart.

A split second later, a small delay occurs, and this delay is going to be caused by insulating material. It is going to be most effective to have the heart contract as two separate units, a top unit and a bottom unit. In order to delay slightly the spread of impulses from the atria to the ventricles, there is a layer of connective tissue, between the top half of the heart and the bottom half of the heart that essentially prevents impulses from traveling. However, in order for the cells and the ventricles to be active, they must receive a signal, and this signal will ultimately come, by way of the atrioventricular node. Basically, in the geographical center of the heart, there is a small group of cells, that will collect impulses that have been delivered from the pacemaker, and direct these impulses down into the larger ventricles. The atrioventricular node, send impulses down through a specialized branch of cells that looks like a small cluster called the atrioventricular bundle. Oftentimes, these bundles do not operate properly, and you end up with what is called a branch bundle block. If these branches in anyway become hindered or inactivated certain regions of the heart cannot be stimulated. Last but not least, from the atrioventricular bundle, impulses are delivered to the discreet minute tissues in the bottom of the ventricles, through small microscopic fibers called Purkinje fibers.

So to review the pacemaker, the atrioventricular node, sets the tone. Impulses are collected by the atrioventricular bundle and delivered down through the Purkinje fibers. Now, by having two separate events, atrial contraction, followed by ventricular contraction, we essentially allow blood to move in a very effective one way circuit. In fact, this is so effective that your heart pumps about 2000 gallons of blood in this way every day. From the heart, blood is going to enter a series of arteries.

Arteries are defined as structures that carry blood away from the heart. That "A" in artery and "A" in away are great clues. As blood flows away from the heart through the series of arteries, specific tissues are supplied by smaller and smaller branches. In order for the heart to operate most effectively there has to be pressure in these vessels at all times. Your cardiovascular system is a closed loop. At no time are you losing large amounts of fluid, or at no time are you gaining large amounts of fluid. Lets talk for just a moment about vessels again. As we said, arteries carry the blood away from the heart, and there is a difference in size between many of these vessels. The largest tubes, and you can think of them as simply hollow tubes, are known as arteries. Arteries branch into smaller hollow tubes, just like the branches of a tree, as you move out from the trunk you get consecutively smaller and smaller. The smaller branches are known as arterioles. Arterioles, finally, branch into the smallest pathways in the system. The smallest pathways are known as capillaries, and they will be special for several reasons. First of all, capillaries are going to be found at sites of exchange in the body. When a tissues needs oxygen, or when a tissue needs to give off carbon dioxide, in order to facilitate that exchange, we must rely on small tubes that things move easily into, and that things move easily out of.

So there are many different sites of exchange in the body. The list of capillary networks is literally endless. After exchange occurs, usually the good things in blood, and I use that term loosely, the good things like glucose and oxygen have been delivered by the cardiovascular system to those tissues. Although most of the work is done at this point, wastes build up in every single cell of your body at every moment of the day. In addition to delivering the nutrients, and oxygen, your cardiovascular system also specializes in delivering wastes away. So if we start at a site of exchange carbon dioxide, a gas, is dissolved in blood, and it continues to go back up to the heart. So this is kind of the second half of the loop. From a capillary network we’re going to have… excuse me. Capillaries will emerge to form venules, which are smaller tubes that carry blood toward the heart, and venules will merge to form larger structures called veins, which lead back to the heart.

So I think to review, away from the heart we have arteries and arterioles. Arterioles then branch to form capillaries. After exchange occurs, capillaries will merge to form venules, venules will grow into larger structures called veins, and veins will ultimately be responsible for delivering blood back to the heart.

One of the unique attributes of blood vessels, most of them by the way, is that they do contain a little bit of muscle. So we’ve got miles and miles of tubes in our heart, and because they contain muscles, they have the ability to change size. Well you ask why would a blood vessel want to change size? It is often advantageous to send more blood through an artery for some emergency, and it become necessary in the case of an injury to send less blood, for example, through an artery. Smooth muscle, the type of muscle that’s found in these tissues, have a couple of things that are sort of similar or in common with cardiac cells. First of all, the smooth muscle in your blood vessels is non-voluntary. That is, you cannot consciously think about smooth muscles and cause them to contract. Secondly, smooth muscle cells are also autorhythmic, that means they can generate some of their own action potentials, and most importantly, they can carry those potentials through tissue to adjacent cells. So, we’ve got this closed system, and we can increase and decrease the size of the tubes that carry blood around frome the heart… or excuse me, from the heart back to the heart.

Last but not least, we have to focus just a moment on capillaries. We always find capillaries at sites of exchange, because they are extremely small and delicate. Cardiac tissue is fairly robust in many cases, except when we are talking about capillaries. These are going to be small microscopic tubes, that consist of only one thin layer of cells. Because they are so small and delicate they’re potentially damaged very easily and we have to be careful what we do with them. But because they are so small and thin, they readily facilitate a process called diffusion. Diffusion will be defined as the movement of material from areas of high concentration towards areas of low concentration. For example when a tissue’s oxygen arrives, oxygen diffuses readily out of these small tissues. When a tissue builds up carbon dioxide and needs to get rid of it, carbon dioxide readily diffuses, moves from areas of high concentration to areas of low concentration, into blood vessels and then carbon dioxide can begin its journey back towards the heart.

So what we see is, to wrap things up, we’ve got two basic components. We’ve got a heart that’s basically a series of four chambers that work in a coordinated fashion to pump blood out of the body. When blood leaves the body, we’ve got arteries and arterioles that carry blood towards tissues. Capillaries are unique because they are always found at sites of nutrient and waste exchange. And last, but not least, we’ve got venules, which become veins that carry blood back up to the heart.

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