Heart: Different Circulations

00:00 Now, first of all, let’s just try and understand the structure of the heart. On the right-hand side, you can see a diagram. This is a diagram explaining the internal structure of the heart as if you are looking at a person standing in front of you. So, look at this slide and just try to identify, firstly, the left atrium and the left ventricle, both towards the right-hand side of this slide. Once you’ve identified those two chambers of the heart, then move towards the other side and identify the right atrium and the right ventricle. Having done that, you’ll then identify the four chambers of the heart, which I’ll describe in a moment.

00:55 But then look and see where the aorta lies. It’s labeled red, and also underneath that aorta is a blue colored structure. That’s the pulmonary trunk. They are important structures that I’ll deal within a moment. Now, try and identify the SA node or the sinoatrial node, and you can see very pale lines running from that node extending into the right atrium and the left atrium. They’re going to represent part of the conducting system I’m going to refer later. And finally, look at the blue circular structure towards the center of the heart, towards the center of the diagram. That’s called the atrioventricular node, and that initiates also conduction of impulses into the ventricles. And those impulses travel through certain bundles that are shown there in blue. And I’ll again refer to this later on.

02:02 So that is really just to orientate yourself with this diagram, so you can have some clear understanding of the structures we’re going to talk about later on. There are two sorts of circulation. Firstly, there is a pulmonary circulation. This is the circulation whereby the heart receives blood from the rest of the body and then pumps that blood to the lungs. It’s the deoxygenated blood. It then passes through the lung and becomes oxygenated.

02:39 And then it’s returned back to the heart, to the left side of the heart, where that oxygenated blood is finally pumped from the heart to the rest of the body. The pulmonary circulation just refers to that circulation of blood to and from the lungs, whereas, the systemic circulation refers to the circulation of blood to all the organs of the body from the left side of the heart. There is also portal system components in the cardiovascular system. These are very strange diversions from the typical supply of blood to blood to tissues. And again, I won’t mention them here except to label them on the left hand side to remind us that there are these different systems, particularly in the liver, and particularly later on when we look at the pituitary gland as part of the endocrine system. Now, I just want to make sure that we are aware of how blood flows through the heart. So on this diagram, again, refresh your memory of the chambers, and I will just briefly go through how blood flows through the heart. First of all, blood passes back to the heart from systemic tissues and enters either through the superior vena cava which is labeled 1 here or via the inferior vena cava which is not labeled or shown in this diagram. But the essential idea is that blood passes through these two vena cava into the right atrium, labeled here 2. And that right atrium then pumps that blood into the right ventricle through a valve.

04:47 And that right ventricle then contracts and sends all that blood through the pulmonary trunk to the lungs, where, as I mentioned before, it becomes oxygenated. And that blood then returns nearly oxygenated into the left atrium, where it passes from the left atrium directly into the left ventricle of the heart, and the left ventricle contracts and passes blood out through the aorta to the rest of the body. So that’s the sequence of blood flow through the heart. Remind yourself of the physiology of the heart and the pumping of the heart, the atria contracting together, and the ventricles contracting together.