As we recall, this is the organ that pumps blood throughout the body, supplying oxygen to all the cells so they can perform aerobic respiration. But what does it really look like inside the heart? How would it feel to be a red blood cell, navigating all the chambers of this organ? It’s one thing to know the names of all the components and how they work, but it’s totally another to have the experience for oneself. So let’s do precisely this, let’s shrink ourselves down and take a journey through the heart. But not so fast, before we head inside the heart, let’s recall a few things about the circulatory system, so that we can have our bearings along our way. When you breathe in, the blood inside the capillaries in your lungs becomes oxygenated, which then goes through the pulmonary veins to enter the heart. The blood will enter the left atrium, and then move through a bicuspid atrioventricular valve, to enter the left ventricle, and is then pumped out of the heart through the aortic valve and into the aorta. Some of the blood will move up into these three vessels, the brachiocephalic, left common carotid, and left subclavian arteries. These are the vessels that carry oxygenated blood to the upper part of the body.
The rest will move into the descending aorta, headed towards the lower part of the body. Continuing along the various arteries of the body, blood unloads oxygen at all the capillary beds, becoming oxygen-poor in the process. It then travels through the veins, culminating in the vena cava, to get back to the heart.
The blood will now enter the right atrium, and then move through a tricuspid atrioventricular valve into the right ventricle, where it is then pumped through the pulmonary valve into the pulmonary arteries and back up to the lungs, so that it can become oxygenated again. The short loop from the heart to the lungs and back to the heart is called the pulmonary circuit, and the longer trip from the aorta to the vena cava is called the systemic circuit. Now let’s make sure we are clear on the path that we will take on our journey. We are going to start out by swimming in the oxygen-rich blood at the end of the pulmonary circuit, using the right pulmonary vein to enter the left atrium. From here we will move into the left ventricle, and then out the aorta. Then separately, we will find ourselves in the superior vena cava, entering the right atrium, and then the right ventricle, finally exiting through the left pulmonary artery on our way to the lungs. So with our path outlined, let’s shrink way down for a closer look. So here we are, having just entered the left atrium of the heart from the right pulmonary veins. To the left we can see the openings of the left pulmonary veins arriving from the other lung, as well as the left atrial appendage. And to the right we see the bicuspid valve with its two flaps, which will take us to the left ventricle. Once inside we turn around, and to the right we can see the bicuspid valve we just passed through. To the left we can see the aortic valve, which will take us out of the heart and into the aorta. Now in the aorta, we will pass under the openings of the brachiocephalic, common carotid, and subclavian arteries that head to the upper body. But we will continue along the aorta, heading towards the lower part of the body. And that completes the journey for oxygenated blood. Now we will imagine this blood moving through all the arteries, delivering oxygen to all the various parts of the body in the capillary beds, and then moving back up through the veins. Now let’s envision ourselves within the oxygen-poor blood that is returning to the heart. So here we are, in the superior vena cava, entering the right atrium of the heart. We can see the tricuspid valve with its three flaps, which will take us into the right ventricle, and we pass through it. Now looking up, on the left we can see the tricuspid valve that brought us into the right ventricle, and to the right we can see the pulmonary valve that will bring us out of the heart and into the pulmonary trunk. Now once in the pulmonary trunk we can see the fork in the road which initiates the two pulmonary arteries. We will turn into the left pulmonary artery, and be on our way to get oxygenated once more. So that concludes our journey through the heart. Hopefully, we now have a bit of insight as to what it might feel like to be a red blood cell, and we have a better understanding of the structure and function of the heart.