In this video, I'll be talking about the anatomy of the heart, including its external structures and its internal anatomy. The heart is composed of four hollow chambers. There are two superior smaller atria, and two inferior larger ventricles. The anterior part of each atrium forms an auricle, it's a wrinkled flap-like extension, sort of resembles an ear. The right atrium feeds the right ventricle, which feeds the pulmonary trunk, which feeds into pulmonary circulation. The left atrium feeds the left ventricle, that feeds the aorta, which feeds into systemic circulation to the body. We'll look at the anterior external heart anatomy. We can see the two atria which are marked by these auricles, these flap-like extensions, and over here is the auricle of the left atrium, looks sort of like that uh that wrinkled ear-like appearance, and then down below is the left ventricle and the right ventricle. The right atrium feeds into the right ventricle, which feeds into the pulmonary trunk, which goes to the pulmonary circulation. The left atrium feeds into the left ventricle, which feeds the aorta, which feeds the systemic circuit. The coronary sulcus, left and right, is the groove that separates the atria from the ventricles, and the interventricular sulcus is a groove that separates the left and the right ventricles. From this view we can see all four chambers: the left and the right atria, the left and the right ventricles, and we can see the great vessels that enter and exit into the heart at its base, at the top here, and the superior vena cava and the inferior vena cava which are bringing deoxygenated blood into the right atrium. We can see the pulmonary trunk, which is the exit from the right ventricle, then the pulmonary veins, right and left, are bringing oxygenated blood from the lungs to the left atrium. Blood travels into the left ventricle and then out from there through the aorta. So those would be the great vessels. On the posterior side we're getting a view of these four chambers and of the great vessels again. So we have left atrium, right atrium, left ventricle, right ventricle, have the coronary sulcus that's dividing the atria from the ventricles, and the interventricular sulcus dividing the two ventricles from each other. We're still seeing those great veins, or great vessels at the superior vena cava, inferior vena cava, and the pulmonary trunk leading to the pulmonary arteries, and then blood coming back to the heart through those pulmonary veins into the left atrium, and out of the heart through the aorta leaving the left ventricle. So the heart has four hollow chambers: a right atrium, a right ventricle, a left atrium, and a left ventricle. The heart also has four valves that ensure one-way flow of blood. There are two atrioventricular or AV valves. These are between the atria and the ventricles. The closure of these valves makes the first heart sound "lubb" then there are two semilunar valves at the base of the great arteries, that is, at the exits from the ventricles and their closure causes the second heart sound "dupp". It's common to represent the sound of the heart as "lubb-dupp", that's their normal heart sounds, as heard through the stethoscope. We'll take a look at this internal anatomy. You can still see the four chambers: right atrium, right ventricle, left atrium, and left ventricle, and now we can get a view of some of these valves. Over here, the right atrioventricular valve also known as the tricuspid valve, controls flow of blood from the right atrium to the right ventricle, and then flow of blood from the right ventricle is controlled by the pulmonary semilunar valve. Flow of blood from the left atrium into the left ventricle is controlled by the left atrioventricular or AV valve; it's also called the bicuspid valve or the mitral valve, and then the flow of blood out into the aorta is controlled by that aortic semilunar valve. I'm now going to go through the chambers of the heart. I'll be talking a little bit quickly because I'm double dipping with our lab material from the heart. The right atrium, the first chamber, receives venous blood from the heart and from the systemic circulation through three large veins: the superior vena cava which collects blood from the body superior to the heart, the inferior vena cava which collects blood from the body inferior to the heart, and the coronary sinus which collects blood from blood vessels that nourish the heart itself. Inside of the right atrium we'd find pectinate muscles. These are ridges on the internal surface of the atrial wall, and at the exit of the right atrium we'll find the right AV valve or tricuspid valve that ensures a one-way flow of blood from the right atrium to the right ventricle. So here's the right atrium, the ridges on the wall would be the pectinate muscles, and then we're seeing that one of the cusps of the right AV or the tricuspid valve, and then we'll follow the flow of blood through that right AV valve and into the right ventricle. The right ventricle receives deoxygenated blood from the right atrium. In the right ventricle we'll find a wall that is the interventricular septum, that's a thick muscle wall between the right and the left ventricles. It prevents mixing of oxygenated and deoxygenated blood. The inner wall of the ventricle displays irregular muscular ridges that are called trabeculae carnae. They make the wall irregular, it reduces suction that would be generated as the heart expands, so it helps to prevent sucking blood into the ventricles as they relax. In the ventricles we'll also see the papillary muscles. These are cone-shaped projections that are anchoring the chordae tendineae. The chordae tendineae are these little strips right here. The chordae tendineae are fibrous connections that attach muscle to the atrioventricular valve and prevent the cusps from flipping into the atrium when the ventricle contracts. At the exit from the right ventricle we find the pulmonary semilunar valve. This ensures a one-way flow from the ventricle to the pulmonary trunk, which is the start of the pulmonary arteries. These arteries bring blood from the heart to the lungs to pick up oxygen. Arteries are always carrying blood away from the heart, and these pulmonary arteries are the only arteries that carry deoxygenated blood. In the body all of the arteries of the systemic circuit are carrying oxygenated blood. Going to take a quick look at this function of the heart. Up here would be the auricle of the right atrium, over here this wrinkled flap would be the auricle of the left atrium, down here is the right ventricle, and over here is the left ventricle. This wall between them would be the interventricular septum, and what I'm showing here is the beating of the heart, and the contraction of the ventricles, and what it's meant to show is these papillary muscles that anchor the chordae tendineae and that prevent backflow through these valves. The chordae tendineae, they're colloquially known as the heart strings, they're tendon-resembling fibrous cords of connective tissue that are connecting the papillary muscle to the tricuspid valve and to the bicuspid valve, the atrioventricular valves. They don't close the valves, and they do not open the valves, but they hold them in the closed position when the ventricle is contracting. It prevents them from flipping back up into the atria. Now we're looking at the right ventricle here. We can see that the entrance to the right ventricle is that right AV valve secured by chordae tendineae, which are attached to papillary muscles. What you can also see are the trabeculae carnae that make the surface of the the interior surface of the ventricle irregular. Once blood has gone through the pulmonary circuit it comes back into the heart and into the left atrium. Oxygenated blood that's coming from the lungs travels through the pulmonary veins to the left atrium. Veins are returning blood to the heart. These are the only veins in the body that carry oxygenated blood. Left atrium, pretty similar to the right atrium, it has pectinate muscles that make the interior surface irregular, but it doesn't have that coronary sinus, that entrance for deoxygenated blood coming from the heart itself that was found in the right atrium. At the exit to the left atrium, we'll find the left atrioventricular valve that controls flow through the opening between the left atrium and the left ventricle. It's also referred to as the bicuspid, meaning two flaps, or the mitral valve, and this valve is forced shut when the left ventricle contracts. Here's the left atrium looking pretty similar to the right atrium, without some of those features that the right atrium has. We'll find some pectinate muscles within the left atrium, and then blood will flow through the left AV or the mitral valve, which is forced to, which is forced shut when the left ventricle contracts. The left ventricle pumps blood through the entire systemic circuit, all the way up to the head, all the way down to the toes, so it generates very high pressure. This is because the muscle wall, the myocardium, is approximately three times thicker than on the right. The aortic semilunar valve is located at the exit from the left ventricle, it controls flow from the left ventricle to the aorta, and it's located at the superior end of the left ventricle. In the left ventricle right here, we'll see the trabeculae carnae, those meaty beams, we'll see papillary muscles, we'll see chordae tendineae. What we'll see is a really really thick myocardium, look at how thick it is on that left side compared to the right side over here, which only has to pump through the pulmonary circuit. The exit from the left ventricle is sort of obscured by the pulmonary trunk right here, it's that aortic semilunar valve leading to the aorta. So blood flow through the heart can be listed out like this, and here i'm using different colored text to indicate the oxygenation or deoxygenation of blood. The first step is, we're following a path of a deoxygenated red blood cell, it would be coming into the right atrium through the superior or the inferior vena cava or through the coronary sinus. From the right atrium it would go through the tricuspid valve also known as the right AV valve and into the right ventricle. That deoxygenated red blood cell would then go through the pulmonary semilunar valve and into the pulmonary trunk and out to the pulmonary circuit. At the lungs it picks up oxygen, gets rid of carbon dioxide, and returns to the heart through the pulmonary veins, and enters into the left atrium. From there passes through that left AV or bicuspid valve and into the left ventricle, and leaves through the aortic semilunar valve, through the aorta, and then heads out to the systemic circuit, where cells are picking up oxygen at capillary beds. This is a step-by-step process that you should really learn and know by heart because it only gets more complicated from here!