Variation in Anatomy & Physiology - Video Tutorials & Practice Problems
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Variation in A&P
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As you go through anatomy and physiology, you're gonna be learning all sorts of facts and figures and it's important to ask exactly who do these facts and figures apply to? 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, uh or some textbooks say that it's somebody who's 22 years old. So it's somebody who's 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 don't, probably don't need to know these figures exactly. But for a female, the reference body is 5 ft four and weighs 100 and £25 for males. It's 5 ft nine and weighs 100 and £55. 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 ft four or 5 ft nine. 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, there's variation in 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 gonna 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 all right, 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 mean different things and, 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 gonna 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 five vertebrae, but about 2 to 3% of people have either four or six. 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 5000 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 your back. It'd be weird if there weren't, it doesn't cause them a problem. I'm gonna say that's kind of part of normal human variation. The other way we, we can ask about normal is doesn't 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. All right, going forward. Just remember we're learning anatomy of this specific body for a reason. It's gonna make it so that you can learn this, 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.
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example
Variation in Anatomy & Physiology Example 1
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3m
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This example starts by saying that the most commonly cited cause of medical error during surgery is quote anatomical variation. All right, I just want to pause there for a second. The most commonly cited cause of medical error is that people are different. That kind of blows my mind a little bit. But let's keep reading. There are 10 named variants in the arrangement of blood vessels that lead to the kidney and the gallbladder. The three most common are shown in the image to the right, the locations of the right hepatic artery or Rh A and left hepatic artery or LH A are labeled in each image right before we look at the image, let's see, just see what it's gonna ask us. It says using information from the image. Why do you think textbooks usually only present one blood vessel branching structure? That's A and B. It says, why do you think that may sometimes be a problem? All right. So with that in mind, let's look at the image. All right, we have uh a blood big blood vessel running up and down and then we have this sort of complex branching blood vessels coming off of it. We don't really need to worry about all the details of it, but we see the Rh A and the LH A and in the first one, they're sort of branching off at the top and it says that that uh variant is about 55 to 60% of the vari of the population. Now type two looks almost just the same as that. But you can see here, the LH A is now branching off a completely different place than where it did in type one. And that different branching pattern represents about 10% of the population. Now, let's look at type three also representing about 10% of the variation. Well, now the LH A is back where it was originally but the Rh A, the right hepatic artery now branches off from a completely different spot than it did before. Now it's branching off a completely different blood vessel down at the bottom. Ok. So why do you think we only learn one? Well, those three variants, right? There only comprise something like 75 to 80% of the population. There's 10 named variants. I'm just gonna say too much variation to know it all, at least in an introductory anatomy and physiology class, right? If you're a liver specialist, yeah, you probably know all 10 variants pretty darn well. Ok. Now, why do you think that might be a problem? Well, imagine you're an, er, doctor, an, er, nurse and you're thrown into this emergency surgery with a stabbing or something near the liver. Do you think that, you know, all 10 named variants, will you be able to recognize the difference and understand exactly what blood vessels you're looking at? It would be really difficult to, right. For the exact same reason. If you're not a specialist on the blood vessels of the liver, there is probably too much variation to know at all. And that can be a problem if that variation is, is really critical to know. OK. With that, just remember, we're learning reference bodies. We're learning the most common. That does not mean that's the only way it is below. We have some more practice problems and I'll see you in the next video.
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Problem
Problem
Name three characteristics of the anatomical reference body?
A
Young, male, 6 feet tall.
B
Female, average height, young.
C
Young, low body fat, average height.
D
Female, 5' 9', 155 lbs.
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Problem
Problem
If variation exists between people, what is one reason we use a reference body to convey information?
A
So that people have a reference for how their bodies should be structured.
B
Using a reference body gives one reference frame, simplifying the amount of information we need to learn.
C
Students studying anatomy are usually young adults, so the reference body is also a young adult.
D
Variation is usually viewed as abnormal and so studied as a part of disease.
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Problem
Problem
Situs inversus is a rare genetic condition in which the internal organs are on the opposite side of the body compared to their normal position. When all the organs are in this flipped position, the organs can often function as normal. Is Situs Inversus a variation of normal anatomy or normal physiology?
A
Variation of normal anatomy because the location of the structures is changed.
B
Variation of normal physiology because the organs function differently.
C
Variation of both normal anatomy and physiology because the changed location changes the function.
D
Neither, because many of the individuals can function perfectly well.
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