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0:00
This isn't your stomach. Your stomach is all the way up here. Instead, this is your abdomen and in today's video with the help of the cadavers here in the lab, we're going to discuss the anatomy of the abdominal region and help you understand exactly what you're feeling when your tummy hurts. Let's do this. [Intro] Let's begin by discussing the musculoskeletal borders of the abdominal region. Now, there's a couple different ways we can actually divide up the abdomen so that
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we have an understanding of exactly what we're looking at. So, in order to understand how we do that though, there's a couple things we have to orient ourselves to. So, obviously, you can see the rib cage here which is also going to include the sternum. So, the ribs that you're looking at primarily are going to be ribs one through ten and then the cartilages associated with them that are going to help attach it to the sternum but we also have
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ribs eleven and twelve which are going to be down here. They just don't have those same cartilages. The next thing we have to understand is going to be the clavicles and I know they're all the way up here and you're probably wondering why we're discussing the clavicles in relation to the abdomen but they will come in handy in just a moment. We're also going to take note of the vertebral column, specifically the lumbar region and the lumbar region is
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made up of five different lumbar vertebrate which we would say L1, L2, L3, L4, and L5. Now, we're also going to see a into the sacrum but the sacrum is more associated with the pelvic region which we're going to be discussing in a future video but then on either side of the sacrum, we can see the Os Coxae. Os Coxae just means hip bone but it's actually made up of three different bones that are fused together. So,
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this upper portion is going to be the one that's most relevant to us and this is going to be the ilium and we're really going to be looking at this ridgeline which is called the Iliac Crest. That's going to be super useful in helping to determine the borders of that abdominal region. So, the first way we can kind of divide it up is the way that I learned and it's the more simple way to do it but we're going to see that it also comes with
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some issues and it's called the Four Quadrant Scheme. So, to understand it, there is a line that would be going down in the midline of the body. So, right through the sternum, through the xiphoid process which is that pointy bit and then it's going to go down to the Pubic Symphysis which is what connects the two pubic bones of the Os Coxae. The next line is a transverse line that would be going right about here. It would
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be going right through the middle of the umbilicus or the belly button. So, what you end up with are four quadrants and that's what makes up the abdominal region. So, we would have a right and left upper quadrant and then a right and left lower quadrant and for me, when teaching basic anatomy, I find that to be sufficient to help kind of describe to my students the locations of the various structures inside of it but from a clinical perspective,
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it's actually pretty insufficient and that's where we then move into the Nine Region Scheme. The nine region scheme is a little more complicated. So, what we're going to do, this is where the clavicle is come in handy. We're going to go all the way up to the clavicles and find the exact middle of it and then, we would draw an imaginary line going straight down and it would go through a
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piece of soft tissue that is obviously absent here on Geoffrey which is called the Inguinal Ligament. So, if we get a line going from the middle of the clavicle down to the middle of the inguinal ligament, that is called the Midclavicular Line and there would be a right and left midclavicular line. The next line is actually called the Lntertubercular Line and that is a line that goes from the tubercle of the iliac crest. So now we're getting back
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to this ridge line that I discussed earlier. There's kind of a bump on the side here. If we had a line that was going across and through the vertebral body - this going to be the body, the vertebral body here and going to the other tubercle, that is that intertubercular line. Then this is where there's a little bit of variability depending on who you ask. The next line we could draw would be another horizontal line that would be going just
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below the 10th cartilage here and that is called the Subcostal Line but there's another line we could also draw that was just above it called the Transpyloric Line. So, what would be right here is the stomach and at the end of the stomach is something called the Pylorus and if we had a line going straight through the pylorus, that's that transpyloric line. So, either you could use either the subcostal or that transpyloric line. Some people will use
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both lines to just help for subdivide it but it really just kind of depends on who's teaching it but by having those lines, so again, we have the two mid clavicular lines and then we have that intertubercular line then we have the subcostal line and that transpyloric line - let's just say, by doing that, you then end up with nine regions in which we can divide the abdomen. So, if we start by just going right down the middle, up here is what's known as the
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Epigastric Region then right below it would be that umbilical. This is again where you'd find the belly button and then below that, that's where we'd find the hypogastric region. If we come up here, this is where we have the right and left hypochondriac regions. Then, on either side of the umbilical region is where we'd have the right and left lateral or right and left lumbar regions, which make sense because they are associated with the
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lumbar vertebrae and then, if we came down here, we'd have the right and left inguinal regions. Now, the reason why this nine scheme, nine region scheme is more useful from a clinical perspective is because it helps you dial in where someone might be feeling pain or referred pain patterns. So, if the clinician was palpating this area here and the - and the patient was presenting with pain, that is known as epigastric pain and that typically is going to you know,
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align with a few different conditions and so that's very helpful from a diagnostic perspective and then one that a lot of people understand is if you have pain down here in the right inguinal region, well, that strongly correlates to appendicitis. So, further subdividing it is helpful from a clinical perspective but again, going back, if we're just teaching basic anatomy, I personally find that four quadrant
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scheme to be adequate to help understand where the anatomy is. Let's now go ahead and look inside the cadavers and see the anatomy of the abdominal cavity. Real quick, I want to thank the sponsor of today's video, KenHub. Ken Hub is an online platform that brings together multiple effective learning tools to help you better understand and learn human anatomy. Anatomy is a truly wonderful science but it can be challenging to learn to say the least.
6:25
Historically speaking, students would have to rely on their textbooks and their note taking skills to get them through the course. KenHub, however, has found an immersive way to expand upon this. You can navigate their platform like an anatomy Atlas, clicking on specific regions to investigate. They then have a combination of articles and videos which act like a textbook as well as an instructor walking you through the lesson and if that wasn't enough,
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they also have quizzes that are some of the most thorough I've ever seen utilizing images, text, and even sound as a narrator will say the anatomical terms out loud. On top of that, the quizzes come in multiple formats and are even customizable. They can come with basic and advanced identification, can be worded more like an exam or can be an intelligent mix where you can choose which one meets your needs the best.
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The quizzes learn from your mistakes which can put an emphasis on previously wrongly answered questions. In preparation for this video, I refer to their abdominal anatomy section. It was awesome. KenHub is so thorough and engaging. It's a fantastic resource for those going through school needing to study, those who have already gone through school and just need a refresher, and those super nerds out there who just want to know as much about their body as they possibly can.
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If you're interested, click the link in the description below they'll give our audience a 10% discount on KenHub Premium. Seriously, if you're looking to actually learn your anatomy, KenHub is the place to go. Again, that link is in the description below. And before we discuss the internal anatomy of the abdomen, let's first orient ourselves to the muscular wall of the abdomen. Now, first and foremost,
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what you're looking at here is going to be the umbilicus or the belly button. Now, the reason why we left it here is to give you just an idea of the depth between the skin and the muscles. Now, if you remember what we're talking about the quadrant anatomy, we had that line going down the mid line which would go through the umbilicus and go down towards the pubis and then we had another line that would be going
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transversely through the umbilicus and so that would create those four quadrants. So, this also is just helping to orient us to what we are looking at here. But the muscle I want to or the first muscle I want to discuss is going to be the Rectus Abdominis. And we can see part of it here. The rest of it is going to be enveloped in soft tissue which is known as the Rectus Sheath. But the rectus abdominis is a paired strap muscle,
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so there's going to be different components to it, different segments to it on either side of the umbilicus and these are strap muscles and what they do is they flex the lumbar vertebral column so you can think of it like doing a crunch. This is going to form the anterior wall of the abdomen. Running down the center of it is what's known as the Linea Alba - just means white line. Now, there is another muscle that is absent on this particular donor that would be in this region
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here the Pyramidalis. Now, pyramidalis is actually going to put tension on the linea alba but it's missing in around 20% of the population and that means that this particular donor is part of that 20%, but it's a very small muscle that is pyramid shaped that puts pressure on that linea alba. So, that will also help form the anterior wall. Now, to form the lateral wall, what we're going to do is I'm going to move this a bit
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so we can see these muscles here. So, this is a small portion of what's known as the External Oblique and it's a pretty massive that will wrap around all the way up onto the thoracic cavity, we can see part of it right here but you'll notice that it's fibers are going towards the midline. This, when it contracts unilaterally is going to help twist the body but if it contracts bilaterally, it will work with rectus abdominis to help flex that lumbar vertebral column. What's
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cool is it's a layered or it's part of a layered system and I can flip this over and what you'll notice, so if you look very closely you can see fibers again going towards the line. Now, they're going away from the midline and this is going to be the Internal Oblique. Its fibers are perpendicular to the external oblique but what's interesting is both of them, including the one that's going to be underneath that we'll discuss in a moment called transversus
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abdominis will turn into a tendon and that tendon is the sheet. It forms what's called an aponeurosis that will then envelop the rectus abdominis creating that rectus sheet. So, all this white tissue here is actually tendon from the lateral abdominal body wall that is just enveloping that rectus abdominis. But to go back to that transversus abdominis, so this one there's only a small bit that we can see here on this
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particular dissection but the fibers are going in the transverse plane. So, when transversus abdominis contracts bilaterally, so both sides at the same time, it compresses the abdomen which is essential for just overall integrity and just you know, stability of this region but if it contracts unilaterally, it can help twist the body but on the same plane as transversus abdominis but if we wrapped all the way around to the back which
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unfortunately we cannot see in this particular dissection is called the Quadratus Lumborum. The quadratus lumborum is the true back wall of the abdomen and I say "true back" because there are going to be two other muscles we'll discuss shortly that are more internal that some may be considered to be part of that wall but I don't personally do that but quadratus lumborum is going to help just again you know, keep with stability,
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it's going to help do some lateral flexion but it is going to be that back wall. So, let's now go ahead and remove what we call the chest plate that also includes the anterior wall of the abdomen. And as I do that, let's slide this out of frame of the camera, we can now see many of the different organs and structures of the abdominal cavity. Now, what separates the abdominal cavity from the thoracic cavity
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is going to be this skeletal muscle here called the Diaphragm. Diaphragm actually translates to fence or partition and it rests on top of massive organ here called the liver but this is just a literal divider between the abdominal cavity and the thoracic cavity but it's obviously going to be essential for breathing but that is part of the respiratory system but this forms the upper border of that abdominal cavity.
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What we also need to understand is there is tissue that lines both the organs and the internal wall of the abdominal cavity. So, if I bring back this chest plate and what I'm going to do is I'm actually going to reflect it over so we can see the inside of it. Now, this is rectus abdominis and rectus abdominis is encompassed again in that rectus sheath but it's also going to be coated on the internal surface with what's known as the Parietal Peritoneum.
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The peritoneum is going to be a serious tissue that is a lubricating tissue. So, it secretes a fluid that is highly lubricating that is going to be very essential for all of the digestive processes but the parietal peritoneum is going to line, the entire, well, not the entire but the vast majority of that abdominal cavity. So, if I pull this again out of frame, that allows us to see in here and then, we have to
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discuss what's called the Visceral Peritoneum. So, this is the small intestine and coating the small intestine is going to be peritoneum that will fully encompass it. So, visceral is just in reference to the guts. So, you're going to have visceral peritoneum that covers all of these intestines as well as liver and many of the different structures inside of you. Now, there's also what are called reflections of peritoneum and this
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is one example of that. This is called the Greater Omentum. Now, the greater omentum is basically just peritoneum that is folded on top of itself, right? So it'd be folded on top of the peritoneum that would be coating the small intestine. Now, if I pull or reflect this liver back, you can see the stomach and the greater omentum would normally be connected to the greater curvature of the stomach. We just dissected that away which
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allows us to see some of the other structures but this is an example of a peritoneal reflection. There's also a less omentum and a couple of other structures that we can't really see here. Another thing we have to understand, if I go ahead and reflect this greater omentum back and then we can see the small intestines. I'm going to move those out of the way. We can see more of the peritoneum here. There's also what are known as intraperitoneal and retroperitoneal structures.
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So, the small intestine are example of intraperitoneal structures. That means they're just fully encompassed in peritoneum but there are other structures such as the kidneys, which I'm actually touching a kidney right now. You just can't see it because the anterior aspect of the kidney is covered in peritoneum. This is an example of a retroperitoneal structure. Only the anterior aspect of it is touching the peritoneum. That also
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includes say the suprarenal or adrenal glands. I can pull this back and if I move the greater momentum back and this reason why we cut this away, it allowed us to then see the pancreas. The pancreas is another example of a retroperitoneal structure. Normally, this would be completely covered by, well, not completely but mostly covered by peritoneum but also, the duodenum is going to be retroperitoneal or again, the vast majority of it.
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So, there are certain structures that are just completely behind this peritoneum and you may be wondering, "Well, what is the peritoneum do?" The peritoneum, and you can this really well in this greater momentum, is a great avenue for blood vessels, lymphatic vessels as well as nerves in some cases. So it's basically just a really good way to get you know, blood supply and innervation to structures throughout the abdominal cavity. That's what that peritoneum is going to be for.
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So, let's now go ahead and discuss the various structures and organs within the abdominal cavity as they relate to that four quadrant and nine region scheme and you're going to see just how useful laying out the abdomen like that is going to be. So, first if we just look at it from that four quadrant scheme which again, for me, for teaching basic anatomy, I do find that to be sufficient. If we do it like that,
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you can see that the liver or at least most of the liver is going to be in that right upper quadrant. Now, this particular liver - I'm going to reflect the diaphragm back - is actually a little bit deformed. This particular donor, we can see some cancer that metastasized from the colon and in fact, this is partially part of their cause of death was going to be colon cancer that metastasized to the liver. So, that does deform the liver and increase its size a bit which means
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that the liver is now projecting into that left upper quadrant but primarily, we would say that it is going to be in the right upper quadrant as would be the gallbladder. Now, I can't show you the gallbladder because this donor have their gallbladder removed at some part of their or some portion of their life but the gallbladder is also going to be in right upper quadrant. Then behind, we would then have the right kidney as well as the right adrenal gland
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are also going to be part of that right upper quadrant. We can also see that the duodenum is going to be partially in that right upper quadrant as it's crossing over. Again, this is where you're - like some of these are not always going to line up perfectly because you have this midline going and the body didn't orient itself based on these schemes that we humans have developed. So, the duodenum can also start to project more towards that left upper quadrant
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but it's going to be mostly in that right upper quadrant but it's also going to start extending into lowers but again, just kind of depends but that is going to be that right upper quadrant. The left upper quadrant, as I reflect the liver back, again partially contains the liver but also will contain the stomach and then I can move it back and we can see the pancreas - that's this yellow tissue here. So, the yellow - so, the pancreas is interesting - it's both the
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digestive and an endocrine organ in the sense that contributes pancreatic secretions to the digestive system but also produces hormones such as insulin and glucagon. Then we of the spleen. The spleen is a really cool interesting organ. It's partially lymphatic in nature but it also - is where red blood cells will end their life at - where it'll rip apart the red blood cells but this is going to be in that left upper quadrant as would be the left kidney and that left adrenal gland.
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Now, the greater momentum is going to be in those lower quadrants but if we reflect that back, you can then see that the intestines are also going to be encompassing both that right and left lower quadrants. Then if we look at the large intestine, now, the large intestine is going to begin here at the cecum and the ascending colon are going to be in that right lower quadrant but then as it goes into the transverse colon,
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which is coming up through here, that is where you're starting to get - and again, if we put this back normally, this is where you're like in the you know, you're kind of like at that border. The transverse colon can start getting in towards those upper quadrants but it's also still kind of in the lower quadrant. So, it really kind of just depends on that individual's anatomy but that transverse colon is going to come around and then we're going to start
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making our ways and move the small intestine into the descending colon which is again, going to be in that left lower quadrant and then we start to go into the sigmoid. From there it's actually going to start dipping down into the pelvic cavity. And again, we're going to discuss pelvic cavity in a future video. The pelvic cavity is going to include you know, the bladder, reproductive tissues, the rectum,
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those types of things but that's where again, we'll leave that for a separate day. I also want to discuss muscles that I mentioned earlier. So, if we look back here, you can see behind the peritoneum, we have the psoas major and this white line, the psoas minor. These are hip flexor muscles that I mentioned. Some consider to be part of the back wall or that posterior wall of the abdomen or the abdominal cavity.
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Now, personally, I don't really see it that way. I just see it belonging inside of the cavity itself instead of quadratus lumbar being that posterior wall but still you can see the right there. Now, and then plus there are plenty of other structures too that we can't see that are retroperitoneal such as the aorta, that descending aorta that's going to go down the inferior vena cava. So, the aorta, which would be about right here running along that left side of the vertebral
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column is going to deliver oxygenated blood to the lower body while the inferior vena cava, which is on the right side heading towards the liver as I bring this back is going to be taking deoxygenated blood back towards the heart from that lower body but then there's accessory blood vessels like the renal artery, renal vein. There's a lot of things that we necessarily just can't see due to the nature of this dissection. But you can see like how the four quadrant anatomy will help.
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Now, if we just briefly discuss then that nine region scheme, you can start to see how clinically that's going to make more sense. So, again, like this region right here is the epigastric region and if I reflect the liver back, you can see the stomach. So, if someone is experiencing some stomach issues, say like gastritis, it makes sense that they would have epigastric pain. Again, if we come down here, as I mentioned earlier, this is the cecum and then we also
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have the appendix. So, the appendix if you have appendicitis, it would make sense that is also going to possibly present with pain in this inguinal region. Now, to really quickly just touch on referred pain, it's also important to understand that these structures don't have, you know, great innervation in terms of sending or your body processing, brain processing nociception pain. Meaning, sometimes the pain can start to like present
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in different areas as of - when compared to their exact locations and that's why it's called Referred Pain. Again, that's a whole, that's a whole other can of worms. Just understand that though when we start breaking down the abdominal cavity into, you know, those nine different regions, it gets a little bit easier diagnostically to start figuring out or at least start trying to figure out where the pain or the issue might be but like briefly
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for to say like in those hypochondriac regions, that's going to be on these right up - right and left upper sides that's where you're getting the spleen, that's where you're getting part of the liver, that's where you're getting part of the stomach. In that epigastric, that's where you're getting part of the duodenum, part of the pylorus, part of the stomach. In the umbilical region, this is where you're getting a lot of the greater omentum but you're
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also getting transverse colon, you're going to be getting part of the small intestines, you're going to be getting a lot of the mesenteric vessels... And by the way, the mesentery is part of the peritoneum as well. This is what anchors the small intestine to the, you know, just to the various blood vessels and to the body itself. So your small intestine isn't just hanging around. But inside of here you're going to find a lot of blood vessels and nerves, lymphatic tissue
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that is all there's going to be a giant network of that behind here in that umbilical region. On the lateral regions, this is - or those lumbar regions, this is where you're finding - this is where you're finding like ascending colon as it's turning into the transverse colon as well as - I move this to the side, descending colon as it's turning into the sigmoid colon. And then when we're getting into that hypogastric region, this is where, again,
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you're still having more small intestine but then the upper portion of the bladder would kind of be pushing into this area. This is, again, part of the pelvic cavity but still you're also going to have the rectum kind of coming around in that area and then in that right and left inguinal areas is where you're also getting the sigmoid as well as you're getting the cecum and the appendix. So, again, from a diagnostic standpoint, it makes a lot of sense to really think
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about it in that nine region scheme but for me personally I find that four quadrant to be adequate when teaching basic anatomy. This is just a small you know, aspect of all the different anatomy and structures inside of here. If we really started pulling this out and teasing it out, you'd find many different structures in here but hopefully this gives you a pretty good understanding of how much is located inside of
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your abdomen. So, again, just to really drill this home, this is not your stomach. This is your stomach. So, when your tummy is hurting, when your stomach is hurting, it's really your intestines but if we're to really figure out what exactly is hurting, that's when we'd have to go, okay, is it hypogastric pain? Is it inguinal pain? Is it umbilical pain? So on and so forth. Thanks for watching everybody. If you enjoy today's video,
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please consider giving it a like. It's a super easy way to help support our channel considering it tells YouTube this video is worthwhile and they're more likely to recommend it to other viewers. Be sure to click the link in the description below and get 10% off your KenHub premium subscription today. Again, thanks for watching and I'll see you in the next video.
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