We're now going to spend some time talking about homeostasis, and homeostasis is probably the key physiological concept that you need to understand for this course. It's going to be the underpinnings of so much of physiology. Homeostasis is the maintenance of a stable internal environment, and we can break that word down. We see that "homeo" comes from the Greek for similar or the same, and "stasis" comes from the Greek for standing still. So inside your body is standing still, unchanging.

That's going to refer to things like fluid levels, nutrient levels, your body chemistry, waste levels, oxygen levels, body temperature. Over here to help you remember homeostasis, we have this picture of a woman out on a cold day and a man out on a real hot sunny day, and I know even though the external conditions that they're in, I know their body temperatures, at least within a few degrees, because they're alive and they're human. Internal conditions are going to be always kept at a set point or at least within a narrow range. Now it's important to think though, homeostasis doesn't mean that your body is just a lump that never does anything. Your body is dynamic, and so sometimes you want to think of this instead as a dynamic equilibrium.

Your body is always changing. Your body is not at a fixed state. Right? Your external conditions are always changing around you. Your body needs to do constant work to maintain all those factors that I was talking about earlier.

Now when your body cannot maintain homeostasis, a failure to do so, we call a disease state, or in anatomy and physiology sometimes we refer to that as pathology. So again, we're going to get into the details of homeostasis and how it's maintained going forward. Let's get to it.