Components of the Cardiovascular System – Introduction to the Cardiovascular System

by Joseph Alpert, MD

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    00:00 Let us move on to the second learning objective. What does it consist of? Cardiovascular system of course consists of the heart, the pump. This is the organ which enables the blood to be transported around the body. The blood is transported in a series of blood vessels starting with arteries moving down into very small blood vessels or capillaries and eventually returns to the heart through the veins. There are also an extensive network of lymphatic vessels that help drain any excess fluid that might escape from the capillaries and we will talk more about that later. The components of the heart are as follows. Let's take a brief, very brief discussion of the development of the heart in embryonic life. The heart starts out as a tube that folds on itself and eventually divides into four chambers during this embryonic state. These are the four chambers that we see in the child and the adult. And the function of course, of the heart is that it is a pump. It makes blood circulate in a never ending circle from the heart to the arteries, the arterioles, the capillaries, through to the venules, the veins and back to the heart to start all over again.

    01:31 The heart is not heart shaped as we might expect the heart on Valentine’s Day. It is really just a cartoon.

    01:39 Here we see a diagram of what the heart really looks like. First of all there are a number of components that make up the heart. We start with the muscle, which is the force factor in creating the pumping action of the heart. There are valves, four valves, to keep the blood moving in a continuous correct direction. If we had no valves, the blood would just slosh back and forth and never get out of the heart and never get out to the body. You have to have valves just like in a gasoline motor engine to keep the gases in the motor moving and to keep the blood moving in the right direction. This electrical wiring that enables the heart to beat in a coordinated fashion as it carries the electrical signal throughout the heart.

    02:35 Then we come to the various blood vessels, the major ones that come to the heart and come from the heart. The aorta leaves the left ventricle so when the left ventricle squeezes blood goes out into the aorta, carried to all the arteries of the body, then the arterioles and then as we said the capillaries eventually working their way back into the venous system and coming back to the heart filled with two venae cavae, the inferior draining the lower part of the body, and the superior draining the upper part of the body. The blood is then pumped out into the lungs through the pulmonary valve and into the pulmonary artery and then in the capillaries of the lung the blood gives up its carbon dioxide, which is just picked up from cells, and it picks up oxygen to take out to the rest of the body in the arteriole system. The heart is surrounded by a tough membrane called the pericardium which protects it and as we said before there are four chambers, two upper collecting chambers, the right atrium and the left atrium. And two lower pumping chambers, the right ventricle and the left ventricle. Remember the right ventricle pumps to the lungs, the left ventricles pumps to the body.

    03:56 Now here we see an actual picture of what the heart looks like in the body. This is a nuclear magnetic resonance image. You can see the black on either side are the lungs and you can see the heart. Notice how close the heart is to the breast bone. The breast bone is up on the top with the spine in the back. Interestingly enough, the right ventricle is the ventricle which is most close to the breast bone with the left ventricle being slightly behind and you can see also where the aorta comes out very, very close to the spine. So this is the real anatomical heart as opposed to the diagrams we have looked at before. Let's talk a little bit about the function of the heart. When the heart beats, there is a sudden increase in blood pressure in both the aorta and the pulmonary artery.

    04:57 And then as the blood travels through the circulation, the pressure falls until the blood arrives in the capillaries and then eventually in the veins. What you see here are three diagrams. First of all, as you might expect the cross sectional area of the cardiovascular system is greatest in the capillaries because every cell in the body has to be close to a capillary. So whereas the aorta, in cross section is much less than the surface area of the capillaries and you can see on the right hand side on the upper figure, in the veins there is also much less capacitance compared to the capillaries.

    05:38 The velocity of the blood in the second diagram increases markedly shortly after the ventricle squeeze and then the velocity slows as the blood arrives in the capillaries and then picks up a little bit in the veins but never goes as fast as it does in the arteries. And you can see the pressure curve in the bottom diagram. You can see the oscillation between systole, that is the squeeze of the heart and diastole and then you can see the sudden drop off in pressure in very, very small blood vessels known as arterioles and then the arterioles feed the blood into the capillaries, then they go into venules and then they go into veins and then come back eventually to the heart. The major resistance in the cardiovascular system is in these arterioles and that is where the pressure drops most powerfully. There are nerve connections and circulating autonomic nervous system hormones that regulate the amount of resistance to blood in the arterioles so that you can constrict them and therefore markedly decrease the amount of blood going through the arteriole or you can relax them and increase the amount of blood going through the arteriole. And of course when they constrict then the blood pressure behind that constricted arteriole goes up and when they relax the blood pressure behind it goes down.

    About the Lecture

    The lecture Components of the Cardiovascular System – Introduction to the Cardiovascular System by Joseph Alpert, MD is from the course Introduction to the Vascular System.

    Included Quiz Questions

    1. Lymph vessels
    2. Veins
    3. Capillaries
    4. Arteries
    1. Aorta
    2. Capillaries
    3. Veins
    4. Lymphatics
    1. Right ventricle
    2. Left ventricle
    3. Aorta
    4. Right atrium
    5. Left atrium
    1. Smooth muscles
    2. Nerves
    3. Arteries
    4. Lymphatics
    5. Veins
    1. pulmonary artery
    2. Pulmonary vein
    3. Superior vena cava
    4. Inferior vena cava
    5. Aorta
    1. Capillaries
    2. Aorta
    3. Pulmonary vein
    4. Inferior vena cava
    5. Pulmonary artery
    1. Capillaries
    2. Venules
    3. Arterioles
    4. Artery
    5. Veins

    Author of lecture Components of the Cardiovascular System – Introduction to the Cardiovascular System

     Joseph Alpert, MD

    Joseph Alpert, MD

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