Variation in Anatomy & Physiology: Study with Video Lessons, Practice Problems & Examples

In anatomy and physiology, the anatomical reference body serves as a standard for comparison, typically representing a healthy 22-year-old individual. This reference simplifies learning by providing a consistent model amidst common variations in human anatomy, such as organ size and body proportions. Understanding normal variation is crucial; while some anatomical differences may be rare, they can still be considered normal if they do not cause physiological issues. Recognizing this helps students grasp the structure-function relationship essential for life, ensuring a solid foundation in the subject.

Variation in A&P

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.

Variation in Anatomy & Physiology Example 1

This example starts by saying that the most commonly cited cause of medical error during surgery is 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 (RHA) and left hepatic artery (LHA) are labeled in each image. Alright. Before we look at the image, let's just see what it's going to ask us.

It says using information from the image, why do you think textbooks usually only present 1 blood vessel branching structure? That's a. And b, it says why you think that may sometimes be a problem? Alright. So with that in mind, let's look at the image.

Alright. We have a big blood vessel running up and down, and then we have 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 RHA and the LHA. And in the first one, they're sort of branching off at the top. And it says that that variant is about 55 to 60 percent of the population.

Now type 2 looks almost just the same as that, but you can see here the LHA is now branching off from a completely different place than where it did in type 1, and that different branching pattern represents about 10% of the population. Now let's look at type 3, also representing about 10% of the variation. Well, now the LHA is back where it was originally, but the RHA, 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. Okay.

So why do you think we only learn 1? Well, those three variants right there only comprise something like 75 to 80% of the population. There are 10 named variants. I'm just going to 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 well. Okay. 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 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 really critical to know. Okay.

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.

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.

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.

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.

Here’s what students ask on this topic:

What is the anatomical reference body in anatomy and physiology?

The anatomical reference body is a theoretical, hypothetical model used in anatomy and physiology to represent a standard for comparison. It typically depicts a healthy 22-year-old individual who has not yet experienced the effects of aging. For females, the reference body is 5 feet 4 inches tall and weighs 125 pounds, while for males, it is 5 feet 9 inches tall and weighs 155 pounds. This model simplifies learning by providing a consistent baseline amidst the common variations in human anatomy, such as differences in organ size and body proportions.

Why is the anatomical reference body important in learning anatomy and physiology?

The anatomical reference body is crucial in learning anatomy and physiology because it provides a consistent model for comparison. This standardization simplifies the learning process by reducing the complexity associated with the vast variations in human anatomy. Without a reference body, students would have to learn about every possible anatomical variation, which would be overwhelming. The reference body helps students focus on essential concepts and understand the structure-function relationship necessary for life.

What are some examples of normal anatomical variation?

Normal anatomical variation includes differences in height, hair color, hair texture, skin color, and body proportions. For instance, some people may have longer arms and shorter legs, while others have the opposite. Additionally, internal variations can occur, such as differences in organ size or the branching patterns of blood vessels. An example is the number of vertebrae in the lower back; while most people have five, about 2-3% have either four or six, which is considered a normal variation if it does not cause physiological issues.

How does normal variation differ from abnormal variation in anatomy and physiology?

Normal variation refers to anatomical differences that do not cause physiological problems and are part of the natural diversity among humans. For example, having a different number of vertebrae in the lower back is a normal variation if it does not affect function. Abnormal variation, on the other hand, causes physiological issues and disrupts normal function. An example is cancer, which, despite being common, leads to significant health problems and is considered abnormal physiology. Understanding this distinction helps in identifying which variations are clinically significant.

Why is it important to recognize anatomical variations in clinical practice?

Recognizing anatomical variations in clinical practice is essential because it helps healthcare professionals provide accurate diagnoses and effective treatments. Awareness of normal variations ensures that clinicians do not mistake them for pathological conditions. Additionally, understanding these variations can aid in personalized medical care, as treatments may need to be adjusted based on an individual's unique anatomy. This knowledge also helps in anticipating potential complications during surgical procedures and other medical interventions.