As you go through anatomy and physiology, you're going to be learning all sorts of facts and figures, and it's important to ask exactly to whom these facts and figures apply. They apply to the anatomical reference body. The anatomical reference body is this sort of theoretical, hypothetical, most average standard body that we use for comparison. The reference body is a young person. Some people, or some textbooks say that it's somebody who's 22 years old, so it's someone who has just entered adulthood but hasn't really experienced the effects of aging yet.
And along those lines, it's a healthy adult. There's nothing physiologically wrong with the reference body. Now, you probably don't need to know these figures exactly, but for a female, the reference body is 5 foot 4 and weighs 125 lbs. For males, it's 5 foot 9 and weighs 155 lbs. You'll note the heights, those are pretty much just average heights at least in the United States.
The weights are kind of low for that height because the reference body has relatively low body fat. So most people, though, aren't 5 foot 4 or 5 foot 9. So why do we use the reference body? We use the reference body because reference bodies simplify learning anatomy, and that's because variation is extremely common. Right?
There's variation in height, hair color, hair texture, skin color, how much body hair you have. Some people have really long arms and short legs. Some people have long legs and short arms. That variation extends within the body.
Some people's specific organs might be bigger than other people's. Blood vessels may branch in slightly different ways or be located just in a slightly different place. If we had to learn all that variation, it would just be impossible, especially in an introductory anatomy and physiology class. So we pick one reference body that we're going to compare everything to. Now, it is really important to note though that extreme variation is rare.
When you look at a person, they look like a person, and that's because of that structure-function relationship. The structures must be able to perform life's functions. If any structure is too extreme, if it's changed too much, it will no longer function properly, and that person won't be able to live. Alright. Before we go on, I just want to talk about this idea of normal variation because we use "normal" kind of sometimes in different ways.
It means different things, and we want to be specific about it here. Defining normal variation can be difficult, and that's because sometimes we ask, well, how common is it? And if something's really rare, we say it's not normal. In this class, I'm going to suggest that that's probably not the best way to think about it. Right?
The example I like, in your lower back, most people have 5 vertebrae. But about 2 to 3 percent of people have either 4 or 6. Now those people will never know it in their lifetime usually unless they have an X-ray of their back for some reason. Now you may say that's not normal, but if you go to a college of 5,000 people, just some basic math tells you there should be at least 100 people walking around your campus with a different number of vertebrae in their back. It'd be weird if there weren't.
It doesn't cause them a problem. I'm going to say that's kind of part of normal human variation. The other way we can ask about normal is does it cause a problem? And if variation causes problems, we kind of think of it as abnormal variation. I can think of this in a physiological sense.
Right? Cancer. Cancer is extremely common. Almost 50% of Americans will develop cancer in their lifetime, but it causes some major, major problems. So we call it abnormal physiology.
Alright. Going forward, just remember, we're learning anatomy of this specific body for a reason. It's going to make it so that you can learn the amount of information you need to know in this course, and you're not overwhelmed with all the variation that's out there. But always remember that variation is common, and nobody is exactly like the reference body. With that, I'll see you in the next video.
