We've been talking about the difference between anatomy and physiology, but, of course, they're often taught in the same class and that's for a very good reason. Anatomy and physiology, we're going to say, are not completely independent. And we can go further and say that they are closely closely linked. And that link comes from what we're going to call the principle of complementarity. The principle of complementarity is a phrase that you might need to know for a test question, but it's much more likely you need to know the ideas behind it really really well.

So we'll break it down. Complementarity, when things complement each other, they go together. They support each other. They build off each other. We can start by talking about anatomy.

Remember, anatomy is the study of structure. So why are things structured the way they are? Well, structure exists in order to perform a function. Why is the heart built the way it is? The heart is built the way it is so that it can pump blood.

Therefore, we can say to understand why an organ is built a certain way, you must understand what it does. To fully understand the anatomy, you need to understand the physiology. So we can come over to physiology. Physiology, the study of function. Why do things function the way they do?

Well, function is determined by structure. Why does the heart pump blood the way it does? It pumps blood the way it does because of the very specific way it is built. So we can say to understand how an organ does its job, you must understand how it is built. To fully understand the physiology, you need to understand the anatomy.

You're going to see this relationship over and over again, phrased slightly different ways, the structure function relationship. Structure determines function, and so on. And this relation is going to come up in chapter after chapter after chapter, and it's really important you keep it in mind. Sometimes, it's easy to think of anatomy as just a list of facts, and then separately, you're going to learn physiology. But if you learn these things together, if you understand that the anatomy that you're learning is there to do a job and the job works because of the anatomy, you're going to have a much deeper understanding of everything.

So like always, we have an example and some practice problems below. Under that, let's go learn something about the body.