 Okay, everybody, Dr. O here. This is a very important video. I'm going to cover the path that blood takes through the heart. This is something that I ask you to know a lot of, that your future instructors are going to ask you to know a lot of. You just kind of have to know the path that blood takes through the heart from words and backwards, I guess you would say. All right, I always like to start with the right atrium as our first chamber. So the first step is that the blood is going to fill the right atrium from the superior vena cava and the inferior vena cava. So all the blood below the heart is going to drain back into the right atrium through the inferior vena cava. All the blood above the heart is going to drain back into the right atrium from the superior vena cava. So we have inferior vena cava and superior vena cava draining into the right atrium. When the right atrium contracts, it's going to help to fill the right ventricle. So blood's going to flow from the right atrium to the right ventricle. Now, 70 to 80% of the filling of the right ventricle is going to be just because of what I mentioned before, how the heart rings and then unrings itself, but the atria are going to contract and they're going to account for about 20% give or take of the ventricular filling. So the blood's going to flow from the right atrium to the right ventricle, through the right AV valve, also known as the tricuspid valve, and that's because it has those three flaps or cusps. Okay, when the right ventricle contracts, that the pressure building up in the right ventricle is going to slam the right AV valve closed, so blood's not going to flow backwards. That's the function of valves to prevent the backflow of blood. So now that those valves are slammed shut, the blood's going to flow from the right ventricle to the pulmonary trunk, and it's going to travel through the pulmonary valve or the pulmonary semilunar valve. So the blood's going to flow from the right ventricle to the pulmonary trunk, and then it's going to flow into the pulmonary arteries where it's going to be carried to the lungs to drop off CO2 and pick up oxygen. So now we're in what's called the pulmonary circuit. Let me show you that. So your pulmonary circuit is the right side of the heart sending blood to and then receiving blood back from the lungs. That's your pulmonary circuit. Now the blood is going to be flowing in through the pulmonary veins that are going to carry blood back into the left atrium. Now we're in what's called the systemic circuit because this side of the heart is going to carry blood everywhere else. So now the blood is in the left atrium. When the left atrium contracts, it's going to force blood into the left ventricle through the left AV valve, also known as the bicuspid valve, also known as the mitral valve. So now the blood is in the left ventricle. When the left ventricle contracts, and this is the biggest, strongest, most powerful chamber we have, when the left ventricle contracts, the left AV valve, the mitral valve is going to be closed. So blood is going to flow through the aortic semilunar valve to the aorta. And then from the aorta, you see here the first branch off the aorta is actually called the brachiosephalic trunk. And then it's going to head into your subclavians and common carotid arteries, et cetera, et cetera. The aorta is going to be connected to every artery we have, all 60,000 miles of blood vessels are going to start right here with the aorta. So that's why I have this other picture I just showed it to you. The aorta is going to branch and it's going to carry blood everywhere else, everywhere but your lungs, right? At least the lungs where it's dropping off CO2 and picking up oxygen. So your aorta is going to carry blood through your arteries. They're going to branch into your smaller arteries and smaller arteries to your arterials. Then there going to be a capillary beds where they drop off oxygen and pick up CO2, then it's going to be carried back to your heart. And now we're back at the superior and inferior vena cava and the whole cycle is going to happen again. So right atrium through the right AV valve, the tricuspid valve to the right ventricle, right ventricle through the pulmonary semi-lunar valve to the pulmonary trunk, then to the pulmonary arteries to the lungs going to come back through the pulmonary veins. Left atrium, then left atrium to the left ventricle, through the left AV valve or the mitral valve or bicuspid valve. And then the left ventricle when it contracts is going to send blood through the aortic semi-lunar valve to the aorta and it's going to go again and again. All right, so very important you know that. Watch this video multiple times. I do want to show you just one more thing quickly. Just a reminder that since the systemic circuit is it needs a lot more pressure to move blood through your entire body, you can see here that the left and right ventricles are quite a bit different. The left ventricle is going to be about three times thicker, much more powerful pump. You'll notice that if you're ever holding a heart when you're dissecting it. So both do their jobs and they both can do it very well. But just remember the left ventricle is much more powerful than the right. Okay, so that is the path that blood takes through your heart. Very important video. I hope this helps. Have a wonderful day. Be blessed.