Episode 43 | SCRIPT

Anatomic Variations in Humans

TAPP Radio Ep. 43 TRANSCRIPT

Episode 43 Transcript

Anatomic Variations in Humans | Fabella | Situs Inversus

Introduction

Kevin Patton: Philosopher Moses Mendelssohn once said, “The essence of the beautiful is unity in variety.”

Aileen: Welcome to The A&P Professor, a few minutes to focus on teaching human anatomy and physiology with host, Kevin Patton.

Preview Episodes

Kevin Patton: In this episode I discuss the fabella bone, situs inversus, and the variety of anatomical variations.

Kevin Patton: Before we get into the topics of this episode, I want to spend just a couple of minutes talking a little bit about the preview episodes. These are short introductory episodes that are released just a few days before the full episode which this is. This is a full episode you’re listening to now. I know that some listeners just skip the preview episodes and only listen to the full episode. And I think you’re missing out on some valuable content when you do that because it’s not just a list of what I plan on discussing in that full episode, although that’s there too.

Kevin Patton: I also give some word dissections, and that’s particularly important for this full episode because we’re using some long convoluted terms that you may not be all that familiar with, things like situs inversus and levocardia and dextrocardia and things like that are going to come up. And if we spend a few minutes sort of dissecting the terms and really looking at how those terms are built and what they mean, that’s a good way to get ready for the full episode and really get more out of it than we otherwise would.

Kevin Patton: In this case, I also am going to be referring to another feature of the preview episodes and that is the book club recommendation. Nearly every preview episode has a recommended book. Sometimes it has something to do with the topic that’s coming up in the full episode. Sometimes it’s not. Sometimes it’s just a generally useful or interesting book for teachers of anatomy and physiology. In the case of the preview episode that came just before this full episode, I recommended a book called Bergman’s Comprehensive Encyclopedia of Anatomic Variation. And so that clearly links in with the topics that I’m going to be discussing in this episode, all of which have to do with anatomic variations.

Kevin Patton: And as a matter of fact, I even talked about the word anatomic and contrasted it with anatomical, and we discussed the usage of anatomic and anatomical. Then went on to discuss physiologic and physiological. All kinds of interesting things are coming up, most of which has to do with topics that are coming up in the full episode. So really, it does get you ready for it. And occasionally, in the preview episode, we’ll get feedback from listeners, or I can answer a question that may have come up about the previous episode, or something else related to the podcast. So it really pays to tune in.

Kevin Patton: I invite all of you to contribute to both the preview episodes and the full episodes by asking questions, answering questions, giving us your take on things or methods that you have used that are useful to you. For example, something we talk about on the podcast might spark an idea about something you do in your class, or maybe you do something completely different and this will give you a chance to talk about why you do it differently and what the advantages are in the way you do it.

Kevin Patton: So if you want to do that, and I strongly encourage you to do that, it’s a lot more fun when you hear more voices besides just mine, just call into the hotline and record it that way. Just call in to 1-833-LION-DEN, that’s L-I-O-N D-E-N, or 1-833-546-6336. Or you can make a recording on your mobile device and just send that sound file to me to podcast@theAPprofessor. Or if you want to write out a message, I can read that or convey that into some way on the air too, but it’s a lot more fun when we actually hear your voice. When you call in, using a mobile phone works just great, but try to do it in kind of a quiet area where there’s not a lot of background noise and also avoid using a speaker phone because that gives a lot of ear vibrations that makes it hard for us to hear very clearly. So I’m looking forward to hearing from you and don’t forget those preview episodes.

Sponsored by HAPS

Kevin Patton: This podcast is sponsored by HAPS, the Human Anatomy & Physiology Society, promoting excellence in the teaching of human anatomy and physiology for over 30 years. Go visit HAPS at theAPprofessor/haps. That’s H-A-P-S. And I’ll see you at the HAPS Annual Conference, right? Maybe at my workshop on Running Concept Lists? By the way, if you are going to the conference, or will ever even just consider going to a HAPS Conference, you may want to check out episode 42. That’s the episode just before this one which is called Kevin’s Unofficial Guide to the HAPS Annual Conference, the 2019 Updated Edition.

Fabella Bone

Kevin Patton: Here’s one of those structures that some folks have and some don’t, the fabella. It’s a bone, but it’s not among the 206 human bones that we usually count as the standard bones of the human skeleton. So let’s take a quick look at what it is and where it is. Then I want to share some recent news about this interesting little bone.

Kevin Patton: In the preview episode that introduces this full episode I already mentioned that the fabella has that name because it resembles a little bean. A bean is fava in Latin and the -ella suffix means little, so little bean. I also said in the preview that it’s a sesamoid bone. We know that sesamoid bones are usually little bones that may or may not develop in the tendons of muscles. The only sesamoid bone that’s among the standard 206 bones that we count in the human skeleton is the patella of each lower limb. Most sesamoid bones are much smaller than the patella and they may be present or not, which is why they’re not common in the standard 206 bones. So here’s a good example of human anatomical variation right here, our bones, how many and what kinds we have.

Kevin Patton: A lot of what we end up with in the human skeleton by the time we reach adulthood depends on how our bones remodel themselves into their so called final form. Sometimes two or more bones that are separate in early development end up fusing together to form a single adult bone. This is normal for the pelves which each start out as three separate bones but normally fuse into a single pelvis bone, one on the left, one of the right. Same with the long bones which start out as epiphyses and a diaphysis that eventually fuse into a single bone. This sort of thing happens as part of the usual course of human development.

Kevin Patton: But sometimes they don’t fuse into a single bone. They remain separated. For example, the left and right ossification centers in the frontal bone of the skull normally fuse into a single frontal bone, but occasionally they instead form a suture between them which results in two frontal bones, not one. This can happen in just about any bone. And when it does, it means that we have a case of anatomic variation.

Kevin Patton: Variation from what? Well, from an arbitrary, perhaps even mythical ideal of a typical human. Really it’s all about numbers. And I’m not sure any one person can identify themselves as “normal” or “typical” but a lot of us are pretty darn close. And anyway, we have to start somewhere in our understanding of anatomy, right? So why not start smack dab in the middle of a spectrum of variation.

Kevin Patton: By the way, this formation of extra skull bones that happens when the typical skull bones don’t fuse completely, happens a lot. In fact, it’s typical. Usually this process forms several very small little islands of skull bone at or near the major suture lines. They’re called sutural bones because of that location. And they really are separate bones. Oh, yeah, and they’re also called Wormian bones if you’re still using eponyms named after the Danish anatomist, Ole Worm.

Kevin Patton: Although it’s not unusual to have sutural bones, they’re not uniform. That is they vary in size and shape and number from one person to another, so they’re not counted among the standard 206 bones of the skeleton. And then there are sesamoid bones called that because many of them are tiny little bones that resemble sesame seeds. These form in the tendons of muscles and could have any of several functions like helping reduce friction within the tendon, helping redirect the force of muscle contraction, maybe helping leverage the mechanical force of muscles like what happens in a patella or knee cap. Or sesamoid bones may just show up and have no function at all. Or worse, they could cause pain or get in the way of normal function.

Kevin Patton: So getting back to the fabella, I also mentioned in the preview that this sesamoid bone sometimes develops in the tendon of the lateral head of the gastrocnemius muscle, just posterior to the lateral condyle of the femur. Some biologists think the fabella can act like a knee cap, helping increase mechanical force of muscles, at least in some primates that’s what happens. There are certain old world monkeys that do this. But perhaps, also, including our pre-human ancestors. But we sort of lost it along the way of evolution with it showing up only rarely now and again as a sort of extra little bone like the others that may show up in some individuals.

Kevin Patton: But some recent news has some folks thinking that maybe the fabella is making an evolutionary come back. That’s because it has become three times more common than just 100 years ago, jumping from, oh, about 11% of the population having one or two fabellea, to up to 39% occurrence in the human population. So 11% to 39%, that’s a significant jump. I know some of us may be thinking, “Can evolution really happen that fast? 100 years?” Well, if you’re thinking that, you didn’t read that book on evolution that I recommended you read in The A&P Professor Book Club a few months ago. It’s called Improbable Destinies. It’s written by my friend, Jonathan Losos. Well, it’s not too late. You can still read it. And when you do, you’ll be amazed at how quickly vertebrate populations can shift their anatomy through evolutionary processes.

Kevin Patton: Well, believe it or not, the fabella is showing up more often in humans. Now you may ask why? What’s it doing for us and why do we need it now? Need it now. Get it? Knee-d, it’s in our knee. Oh man. Okay, so I resorted to puns because I don’t have a good answer to that question of why it’s happening. We’re not sure what it does for us, if it does anything at all. But the team that discovered this increase in the incidence of fabellae, speculate that maybe a shift in nutrition over the last 100 years that caused the human skeleton to get larger and heavier could be putting the components of the knee joint under more pressure, and that’s what’s triggering the formation of a fabella. They also found out that if you have osteoarthritis, you’re more likely to have a fabella.

Kevin Patton: But we don’t know if there’s really any cause and effect relationship with that. We just see it happening. So that may or may not be part of the story. As a matter of fact, there are now just a lot of questions that need to be answered, but interesting and fun questions about human anatomic variation, right? I love science.

Kevin Patton: By the way, before we leave this topic and go on to our next puzzler in the realm of anatomic variation, I want to mention something that this story reminds me of. A very strange phenomenon in the world of human anatomy and physiology teaching. Whenever the idea of keeping up with new and updated science content in A&P teaching and in the resources we use for teaching such as textbooks, I often hear something to the effect that, “Yeah, physiology probably changes a lot over the years. But anatomy, anatomy doesn’t change.” Well, I hear this from students, but I also hear it from A&P teachers.

Kevin Patton: Now I don’t usually agree with folks when they say this to me, but not being a fan of needless contradiction in conversation, I usually do just soft pedal my response by not actually challenging them. But looky here, we have yet another case of human anatomy changing over time, the evolution of human anatomy. Of course, that’s not something we see a lot of, but we sure do see a lot of change in our understanding of human anatomy, don’t we? As more specimens are studied, as more and different questions are asked, as old ideas are challenged, as our technology improves and we’re better able to observe, measure, and explore the structures of the human body, our understanding of human anatomy changes a lot in my opinion. I think we’re better educators if we don’t close the door on updates in human anatomy. I think we’re going to miss some very important ideas if we do that. Just a thought.

Sponsored by AAA

Kevin Patton: A searchable transcript and captions for the audiogram of this episode are funded by AAA, the American Association of Anatomists, at anatomy.org. Hey, I’m a member. Why don’t you consider joining too?

Situs Inversus

Kevin Patton: Regular listeners to this podcast know that I love to tell stories about the olden days. And well, this being a podcast, there’s nobody here to stop me, so I’m going to do it again. Way back in 1995 I was the conference director for the HAPS Annual Conference in St. Louis and I had set up some little mini field trips within the workshop portion of the annual conference. And one of those was a field trip to the medical school at Washington University in St. Louis. They have a very widely known medical school there.

Kevin Patton: I had heard that there was an anatomical museum within the med school that was open to the public but only by appointment. And I couldn’t find anybody that had ever been to it. So I called up the med school and got ahold of the person in charge of it and found out that really what it was is a set of exhibits that they had set up in their dissection lab. I said, “Well, can I have my colleagues come in small groups during our conference and take a look at what’s going on?” And they said, “Yeah, sure. We’d love to have them.” And I said, “Well, is it okay if I come and check it out first myself and kind of get a feel for what to expect in case I get questions?” And they said, “Yeah, come on down. When’s a convenient time?”

Kevin Patton: And so I went down there and met the person who was in charge of it. He walked me down the hall and unlocked the door and let me in there and said, “Just whenever you’re done, just close the door, make sure it locks behind you and I’ll see you around sometime.” And so I thought, “Well, okay.” So I walked in there and, oh my gosh, it was amazing. But I’ll never forget the first thing I saw. I just, I sort of turned away from the door and looked straight ahead and there was a big shelving unit. And it’s that old style museum shelving where it’s a glass enclosed case, but it was really big and right there at eye level was what looked like two human torsos.

Kevin Patton: At first, I thought it was a human torso model like we have in our community college lab where it’s the legs are cut off and sometimes the head is removed, but you can see a little bit of what’s left of the shoulder and then you see the torso, and it’s opened up and you can see the lungs and the heart and the abdominal organs and so on from an anterior perspective. So that’s what I thought I was looking at it first. But then I realized, “Well, this is like an old style model because it doesn’t look all shiny and bright like the usual models.” And then I realized, “No, that’s a museum jar that has an actual human torso in it that’s been preserved and it’s been prosected so I can see those organs like I would in a model.” And what I thought was two big glass jars that contained two torsos, it turns out there was one torso and a mirror, and I thought, “Well, what’s the point of this?”

Kevin Patton: So I start looking more closely at it and considering it, sort of like when you’re at a art museum. Sometimes I’ll glance at a piece of art and it won’t really suck me in. But if I take a moment to look at a painting, it kind of draws you in and you start to see things you would never have seen at just a glance. Well, that happened to me and I realized, “Oh my gosh, this is situs inversus. This person’s organs are completely flipped around in the mirror image,” and that’s why they had a mirror set up. It was sort of, they were at an angle, almost a 90 degree angle, well actually maybe it was exactly 90 degree angle. I don’t know. It was 1995. I can’t be expected to remember every detail. But it was set up in a way that you could see, by looking in the mirror you could see what would look like a normal arrangement of organs. And then when you look at the actual specimen, you could see everything was flip-flopped around, situs inversus.

Kevin Patton: Clearly that was a dramatic and enlightening moment for me because I still remember it from all the way back in 1995. And there were a lot of other very interesting specimens in there. You can imagine over the course of decades upon decades of work at WashU’s medical school, that they would’ve come across some very interesting variations in human anatomy and they preserved some of those. This one happened to be from I think the last half of the 19th century and was still very well preserved.

Kevin Patton: Now in the preview episode, prior to this full episode, we dissected the terms situs inversus and situs solitus and the related terms, dextrocardia and levocardia. We’re going to get to those terms in a couple of minutes and I’ll explain them again very briefly, but I also want to bring up before we do that, a recent news item about a 99 year old woman from Oregon who donated her body for dissection. It ends up that she had situs inversus with levocardia, but she never knew it. Nobody, her doctors, nobody ever knew that she had it. It wasn’t until they got it at the Oregon Health and Science University that they discovered this situation where she had reversed organs except her heart was still facing toward the left.

Kevin Patton: So it wasn’t quite like that specimen I saw at WashU, but it was still a case, a variety of situs inversus. Those anatomy students at Oregon Health and Science University, they got to explore this very unusual variation in human anatomy. Some of you may have seen the poster about this case at the AAA meeting last month. Cam Walker and Mark Hankin had a poster called An Unusual Case of Situs Inversus with Levocardia.

Kevin Patton: So what do we mean exactly when we say that this donor had situs inversus with levocardia? We’ve already mentioned that situs inversus is a variation of human anatomy where the viscera are flipped over into a mirror image of the typical arrangement of organs, which usually on the left is now on the right and what’s typically on the right it’s now on the left. Also, sometimes situs inversus is called situs transversus or situs oppositus.

Kevin Patton: Oh, by the way, situs inversus is sometimes called situs transversus or situs oppositus. Whatever you call it, this condition is congenital, meaning that it shows up during prenatal development. Not something that happens later in life as a result of, oh, I don’t know, doing too many spins on the dance floor. It’s not that. It’s not due to environmental influences like that.

Kevin Patton: It’s found in about 1 of every 10,000 people in the population, so it is rare. It’s not super duper rare, but it’s pretty darn rare. Most of those who have this variation, have what’s called situs inversus totalis, meaning that one’s entire set of visceral organs is flipped over left to right, or right to left, if you want to look at it that way. There’s not any particular danger in having this variation. Well, except, healthcare providers may get really confused when they’re assessing your health. And we know that confusion among healthcare providers could lead to complications, could lead to maybe even some very serious complications. Yeah, there is that downside.

Kevin Patton: Now going back to that young man with situs inversus at the Wash U Med School from the later half of the 19th century, when I read the information in the little exhibit there, I found out that he had died of complications of appendicitis. Remember, his appendix was on the wrong side, at least compared to everybody else. His appendix was on the right left, not on the left right. I’m wondering if right left sided pain and tenderness didn’t contribute to an initial misdiagnosis where somebody said, “No, that can’t be appendicitis. It’s on the wrong side.” Maybe that? Yeah, could of. Ended up costing him his life. [ERROR: In my discussion of the cast of situs inversus in the young man from the 1800s, I mixed up my left and right. Yikes. The appendix is on the right in situs solitus, but on the left in situs inversus. This was corrected in the audio file on 10 May 2019, but the correction may not be heard in all available platforms.]

Kevin Patton: I mean there’s that somewhat well known case of Donny Osmond who was a popular singer and actor of my generation. He had appendicitis when he was 15 and it could’ve been treated before it got as serious as it did if anyone had known that he has situs inversus. As a matter of fact, he was in fact misdiagnosed early on in that episode and it wasn’t until it had progressed to a very serious stage that he got some treatment.

Kevin Patton: But I guess having situs inversus could have some advantages. I don’t know. I mean there’s probably advantages to anything, right? One of the villains in a James Bond novel claims to have survived an assassination attempt because he had situs inversus and the assassin’s bullet missed shooting him in the heart for that reason. Nah, I don’t know, that’s pretty far fetched, as is just about everything in a James Bond novel. But I don’t know, man. I guess could happen.

Kevin Patton: Let’s look at the heart when one has situs inversus. First of all, the heart like many of our organs is chiral. Chirality literally means handedness, which I mentioned way back in episode 30 where I discussed the chirality of cells. Put in another way, organs such as the heart do not have the same structure when you flip them around. It’s like your two hands. They’re not interchangeable because they’re flipped over versions of each other.

Kevin Patton: In situs inversus totalis that would include having the heart flipped over so that the apex is pointing toward the right, not the left. Ordinarily, in most of us, about two thirds of the heart is to the left of the body’s median. That is to the left of the midsagittal plane. But when it’s flipped over, the heart is mostly on the right. This situation is called dextrocardia, meaning heart toward the right. I suspect that the dextrocardia often seen in situs inversus does not really decrease your chances of being assassinated. I’m just saying. But I’m not an expert in assassination, so we’ll just have to leave it there.

Kevin Patton: But sometimes situs inversus occurs where the heart doesn’t flip over. It still points toward the left as it does in most of us. When one has a left pointing heart, it’s called levocardia. That’s what I have. I know because I’ve seen medical images of my heart and it’s pointing to the left, just like I expected. That’s probably what you have too, probably. I mean, it’s what 99.999% of us have. By the way, I sometimes make use of this fact, that I have levocardia. I have a left pointing heart. For example, if someone asked me to do something I really don’t want to do, I may say to them, “I’d love to help you move all your furniture up to the fourth floor. But I’m sorry, I have levocardia.” Okay, that doesn’t usually work, but I have tried such things.

Kevin Patton: About 1 in 22,000 people have situs inversus with levocardia. That’s a little bit more than twice as rare as plain old ordinary situs inversus totalis. Having situs inversus with levocardia is a weirder situation than regular situs inversus because here you have everything but one organ, a complex vital organ, flipped over. I don’t know, sort of like having a left hand on a right forearm. Things aren’t going to work as expected I would think. In some cases, the crossing over of the aorta and pulmonary trunk and perhaps some other structures gets so messed up it can make one more vulnerable to cardiac problems. But, as in the case of that 99 year old body donor and organ, it doesn’t have to cause any problems at all. Heck, it may be that’s what made her live so long.

Kevin Patton: By the way, there is another even rarer situation called situs ambiguous. It’s also called heterotaxy. That’s where things are not a neat mirror image of the typical layout of organs. The liver may be on the midline. The gut maybe oddly rotated from its normal position. All kinds of things could be messed up. As you can imagine, situs ambiguous, depending on exactly what’s out of place, and how different from normal it is, is more likely to put a person at risk for medical complications. Situs ambiguous is by the way a lot more rare than situs inversus which is already pretty rare.

Kevin Patton: Now you’ve probably been thinking, “What causes situs inversus?” It happens when a mother looks into a mirror during pregnancy. No. No, no, no. We’d all have situs inversus if that were true. It’s when she breaks a mirror during pregnancy. Unless she throws salt over hear shoulder. Okay, okay, none of that is true. I think there’s still some unanswered questions about how situs inversus develops. But the last best story states that it’s usually in the genes. It’s considered to be an autosomal recessive condition in which both parents have to be carriers of an altered gene that results in situs inversus. But in some cases, it seems to be X-linked, not autosomal. But either of these patterns of inheritance helps explain why it’s so rare.

Kevin Patton: But the next question is, at least the next question that occurs to me is, what is that altered gene doing, or what is it supposed to be doing that it’s not doing? From what I can tell, we can’t really say for sure. Probably it’s any of several different genes that are involved, so there are likely several different mechanisms that could be at play. One mechanism likely involved in at least some cases is primary ciliary dyskinesia, sometimes called PCD, primary ciliary dyskinesia.

Kevin Patton: During embryological development, the normal functioning of the primary cilia of cells in necessary for normal positioning of internal organs. About half of embryos with PCD develop situs inversus. Individuals that have PCD account for about a quarter of all the cases of situs inversus. So it does seem clear that PCD is not the sole cause of situs inversus, but maybe, maybe the primary cilia are somehow always involved, or maybe a lot of times they’re involved even if it’s not full blown PCD. Or maybe there are other things affecting positioning during organ development that cause situs inversus.

Kevin Patton: Anyway, summing up, situs inversus, a really interesting, dramatic, fun kind of variation to look at, even though it’s very rare.

Sponsored by HAPI Online Graduate Program

Kevin Patton: Distribution of this podcast is sponsored by the master of science in human anatomy and physiology instruction, the HAPI degree. Looking to power up your game in teaching A&P? Check out this online graduate program at nycc.edu/hapi. That’s H-A-P-I. Or click the link in the show notes or episode page.

Kevin Patton: If you’re going to the HAPS Annual Conference, the HAPI program will be well represented there, so you can get all those questions that I know you have answered while you’re there.

Variety of Anatomic Variations

Kevin Patton: Of course, we have anatomic variations. Just look at yourself. Look at your facial features, your hair, your body size and shape, muscle development or lack thereof, your larynx, your eye color, your skin color, breast size and shape, ear shape. These are all examples of human anatomy that varies in our population. We can easily see these. Because we can see them all the time though, they’re kind of invisible to us sometimes. At least when we’re thinking about human anatomy, we think of these variations as part of normal most of the time and we don’t really discuss them much when we study human anatomy.

Kevin Patton: But there are also all kinds of variations inside us too that we may not even be aware of within our body. We’ve discussed a few of these already in this episode, fabella, other sesamoid bones, sutural or Wormian bones, situs inversus and some of the variations of that. There are others that you may already be familiar with, perhaps even a few of which you discuss in your A&P courses, for example a cervical rib. That is one or two little ribs that may be associated with the last cervical vertebra. That occurs in about, oh, 1 in 500 people, and potentially it could put some pressure on the brachial plexus and cause some problems.

Kevin Patton: Or the foramen tympanicum. That’s a little hole between the temporomandibular joint and the external acoustic canal that normally seals up and isn’t even there by adulthood. But it could remain open in as many as one in five people. Probably most of the time don’t do anything, but it could cause issues with the temporomandibular joint, the TMJ. For example, it could allow infections to pass from the ear into the TMJ.

Kevin Patton: Or there’s the median artery. It’s found in about 1 in 12 people. And if it’s present, it’s somewhere between the radial artery and the ulnar artery in the forearm. And having that extra artery there could affect how a surgery goes or the severity of an injury to the forearm.

Kevin Patton: And there’s all kinds of accessory organs like accessory spleens and kidneys and other organs that may show up. And then there’s accessory ducts. For example, a functioning accessory pancreatic duct is somewhat common. Some people are missing typical organs. For example, you could be missing the vermiform appendix, or the pectoralis major, or minor, or both, or maybe you never get wisdom teeth, or maybe the lateral incisor teeth are missing.

Kevin Patton: It’s common for people to have a typical structure. But its characteristics are out of the ordinary. For example, it’s common for people to have a typical structure but to have its characteristics be a little bit out of the ordinary. For example, people could have bones that incompletely fuse, thus remaining separate bones. We kind of talked about that when we discussed sutural bones. Or you could have bones that normally remain separate but they fuse together to form a single bone, for example, that can happen in the coccyx and sacrum. Muscles that may branch or segment or have unusual innervation aren’t all that uncommon either. But which muscles are they and in which people? Well, that varies. It’s anatomic variation.

Kevin Patton: Speaking of innervation by the way, there’s all kinds of variations in the course of nerves in the body. The same is true of the pathways of arteries and perhaps even more so in veins and lymphatic vessels. I could go on and on. Sometimes I do go on and on. But I’ll stop this time.

Kevin Patton: In Bergman’s encyclopedia which I mentioned in the preview episode, the authors go on for nearly 1400 pages, and even then they only barely get through the tip of the iceberg. If you want a list of some of the more well known anatomic variations without looking through a 1400 page book, which is my recommended strategy, but if you don’t want to do that and just learn a quick and dirty list, I have a link to one in the show notes in episode page.

Kevin Patton: We haven’t even spent much time to consider the variations that depend on normal functions of the body. For example, my body and its organs is way different than it was when I was 30. And that body was way different 30 years before that. And will be different 30 years from now. So development and aging is a big factor in the normal spectrum of anatomical variation.

Kevin Patton: What about variations related to sexual development? Male and female bodies when studied in groups have variations within and between the groups, resulting from the influence of hormones and other factors. Look at all the environmental factors that influence anatomical variation. For example, nutrition. I already mentioned that when we were talking about the fabella and how nutrition has allowed our skeletons to be on average bigger than they were 100 years ago. And there’s also things like exposure to environmental agents such as the sun. That can change the color of our skin for example. Or other environmental agents like weather or pollutants or all kinds of things in our environment.

Kevin Patton: And what we ourselves do with our bodies is another set of factors. Consider how we position our bodies as we work, as we rest, as we sleep. For example, right now I’m speaking to you at a standing desk. That’s where I do almost all my work is at a standing desk. My skeleton and muscles and perhaps some other aspects of my anatomy are going to be different than if I had instead been spending all those many hours and days and months and years at a sitting desk at doing those same tasks.

Kevin Patton: So how much and what kind of work do we do has an influence. That could affect our muscles, our bones, our airways, and even our brains. And again, I have to stop myself, otherwise I could just go on and on for ever.

Kevin Patton: But there’s a big and important question behind all of this, and that question is: What is normal in terms of human anatomy? I think it’s safe to say that normal or typical doesn’t even exist in real life human anatomy. Well, okay, it does exist, but it’s not what one would expect in any one real person. It’s sort of an average or a midpoint range of a spectrum. I think this midpoint is a good place to start in teaching and learning human anatomy. You have to start somewhere anyway. Why not with a sort of unrealistic average? Then add layers of knowledge about variations once we’ve laid a foundation on that midpoint that we started with.

Kevin Patton: So how do we do that? Well, the best way is, I don’t know. You tell me what the best way is. I’m kind of thinking there isn’t a best way, a single best way. I’m thinking it’s largely up to us as artists to decide what works best in our situation with our students for this semester in this course, or even with this individual student.

Kevin Patton: Remember, in my world, teaching is both art and science. We are among other things artists. We’re artists of telling stories, stories about the human body. So I think we need to really think about, play with, experiment with different ways of telling our story of human anatomy so that at some point it’s clear that we don’t all look like the idealized sketches in our books and models on our lab bench, or even all the elderly cadavers in our dissection lab.

Kevin Patton: Perhaps we can begin by being clear and intentional about pointing out differences arising from development and aging, from the effects of sex hormones, from environmental influences, from the range of possible human activities or lack activity. Then bring in all those variations in the genetic code and variations in how embryological events unfold. Or maybe for embryology I should say how the embryological events fold rather than unfold.

Kevin Patton: I think in the end the best story of human anatomy is a story of the awesome and beautiful balance of both unity and variety in the human form.

Kevin Patton: As always, I have links to resources, images, and additional information about each segment in all episodes of this podcast. The platform where you’re listening right now may or may not show these links. Or if they do appear, they may not be live hyperlinks that you can click. That’s not a problem though. You can always go to theAPprofessor/podcast and easily find any episode and check out the links and other details in the episode page.

Nuzzel Newsletter

Kevin Patton: Some of the topics I discuss and some of those links I just mentioned regard recent news or recent research publications. Many of those first appear in my daily newsletter of curated headlines for A&P teachers. This daily collection of headlines is conveyed through a service called Nuzzel. That’s N-U-Z-Z-E-L. And the name of my newsletter on the Nuzzel platform is easy to remember. It’s the same as the name as this podcast, The A&P Professor. To find the archive of past newsletters or to get it delivered daily in your inbox for free, just go to nuzzel, that’s N-U-Z-Z-E-L, nuzzel.com/theAPprofessor. Or you guessed it, just click the link in the show notes or episode page.

[NOTE: The updates have been migrated from Nuzzel to Revue https://theapprofessor.org/updates]

Aileen: The A&P Professor is hosted by Kevin Patton, professor, blogger, and textbook author in Human Anatomy and Physiology.

Kevin Patton: All information in this podcast is provided “as is” with no guarantee of completeness, accuracy, timeliness, or of the results obtained from the use of this information.

Last updated: September 23, 2021 at 19:59 pm