This tape shows the internal organs of the thorax and of the abdomen, and the male and female reproductive organs. In this first section we'll look at the organs of the thorax: first the heart, then the lungs. We'll also look briefly at the esophagus.
The thorax itself, the upper part of the trunk which contains the heart and lungs, is shown in Tape 3 of this atlas. Here, we're looking at the contents.
To understand the heart we'll begin by seeing where it is. We tend to put the heart here in our imagination, but in reality it's much closer to the mid-line. Seen from in front, the heart is here. It lies behind the sternum, and directly above the diaphragm.
Seen from the side, the heart is here, occupying almost all the space between the vertebral bodies behind, and the sternum in front. When the diaphragm moves, the heart moves with it.
To get our first look at the heart, we'll start by removing the upper extremities, and all the shoulder muscles that surround the upper thorax, so as to leave just the thorax itself, enclosed by the ribs and intercostal muscles.
Then we'll remove this part of the rib cage on each side, revealing the lungs, which are fully inflated here. When we let the lungs deflate we can see the heart behind the sternum, contained within its protective jacket of pericardium. To see it better we'll take the lungs, the sternum and the pericardium out of the picture.
This is the heart. This is the diaphragm. The major blood vessels that lead into and out of the heart take up almost as much space as the heart itself.
Now that we've seen where the heart is we'll take a detailed look at it. We'll look at its four chambers, and its four valves; then we'll look at the great vessels that enter and leave the heart, and lastly we'll look at the coronary arteries.
Because we so often see simplified diagrams of the heart like this, we tend to think the atria, the inlet chambers, are above, and the ventricles, the pumping chambers, are below. It's perhaps surprising to see that in reality the atria aren't above the ventricles, they're behind them.
Here's the heart in isolation. Here are the ventricles in front, here are the atria behind. This generous coating of epicardial fat makes it hard to see the four chambers distinctly.
To see them more clearly, we'll go to a heart in which almost all the fat has been removed. In this specimen all four chambers have been distended with equal pressure, making the atria somewhat larger than normal. This is a directly posterior view of the heart, this is a directly anterior view. The massive thick walled left ventricle projects forward and to the left. The thinner walled right ventricle is partially wrapped round the left one.
We'll see the ventricles by themselves in a minute. For now, let's go round to the back, and look at the two atria.