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Regions of the abdomen and thorax seen anteriorly and posteriorly.
Hello everyone! It's Megan from Kenhub here, and welcome to our tutorial where we're going to talk about the regions of the thorax and the abdomen.
So you might be wondering why we divide the body up into regions. Well, the reason we do this is so we can provide clear and precise communication of the location of structures, injuries or pathologies. The body is divided into many, many regions so we can't possibly cover them all in one tutorial. We're actually going to cover them across five different tutorials. But, today, as you know, our focus will be the thorax and the abdomen.
So you might want to know what exactly the thorax and abdomen are. Well, these two parts of the body form the trunk of the body or the area you can now see highlighted in green. They're separated by a muscular structure called the diaphragm which sits roughly about here. So, the thorax or the chest is situated above the diaphragm and the abdomen more commonly known as the midriff is situated below it.
So now that we're familiar with these two parts of the body, let's break them down further into their regions. So we're going to start with the thorax and the region you can see here highlighted in green is the infraclavicular region. Now the name gives as a clue of the location of this region. So infra- refers to inferior and clavicular refers to the clavicle. So this region is located inferior to the clavicle. As such, its superior border is formed by the clavicle, its inferior border is formed by the second rib and its medial border is formed by the manubrium. The apices of the lungs are located in this region.
So inferior to the infraclavicular region, we can see this region highlighted in green which is the mammary region. Based on the name, you've probably guessed that this region contains the breasts. So the superior boundary of this region is formed by the third rib and the inferior boundary is formed by the sixth rib. The medial boundary is formed by the lower part of the sternum up until the point of the xiphisternal joint. So essentially, the medial boundary is formed by the body of the sternum. This region can also be known as the pectoral region because obviously deep to the breasts, we have the pectoralis muscles. It's important to note that part of the heart is located in the mammary region on the left hand side.
So inferior to the mammary region, we have another region of the thorax and you guessed it, it's called the inframammary region. The superior boundary of this region is formed by the sixth rib and it's bound medially and inferiorly by the costal cartilages of the sixth to tenth ribs. On the left hand side, the apex of the heart runs into this region.
Now let's move on to the sternal region of the thorax. This is a region that overlies the sternum or the breast bone and it's bordered by the mammary and inframammary regions on either side. The sternal region can be broken down further into two parts –the upper sternal region which essentially overlies the manubrium and the lower sternal region which overlies the body of the sternum. A large portion of the heart is located in the lower sternal region.
Up next, we have the lateral pectoral region. This region extends posteriorly to the dorsal aspect of the thorax which we'll discuss further in our tutorial on the regions of the back and buttocks. So the medial boundary of this region is formed by the inframammary region, the lateral boundary is formed by the axillary region of the upper limb, and the inferior boundary is formed by the hypochondriac region of the abdomen.
We've now officially covered the regions of the anterior thorax so it's time to move on to the regions of the abdomen. There's two methods used to characterize the regions of the abdomen – the first of which is the four region scheme which divides the abdomen into four quadrants. This is done by drawing a vertical line along the midline of the abdomen and a horizontal line along the abdomen at the level of the umbilicus. This divides the abdomen into a right upper quadrant, a left upper quadrant, a right lower quadrant and a left lower quadrant.
The second and more common way to divide the abdomen into regions is the nine region scheme which uses two vertical planes and two horizontal planes. The vertical planes are the left and right midclavicular lines which run from the midpoint of the clavicle downwards towards the midpoint of the inguinal ligament. The horizontal planes are the subcostal plane which runs at the level of the lower edge of the tenth costal cartilage and the transtubercular plane which passes through the tubercles of the iliac crest and the body of the fifth lumbar vertebra. These planes divide the abdomen into a right and left hypochondriac region, an epigastric region, an umbilical region, a right and left lumbar region, a hypogastric region, and a right and left inguinal region. So this method divides the abdomen into nine parts whereas the four region scheme only divides into four. This means that the nine region scheme is more specific and detailed. This can help us further localize clinical symptoms to arrive a more accurate diagnosis. It's for this reason that we're going to focus on the nine region scheme for the rest of this tutorial.
The first region of the abdomen we're going to take a look at is the hypochondriac region which is actually divided into two parts – the right hypochondriac region and the left hypochondriac region which are found superiorly on either side of the abdomen. The superior border of this region is formed by the inframammary and lateral pectoral regions on either side and medially, it's bordered by the epigastric region. Inferiorly, it's bordered by the left and right lumbar regions.
So now we're going to look at the contents of these regions and because they're located on different sides of the body, they're obviously going to contain different organs. I've got to warn you that now we've moved on to the regions of the abdomen, there's going to be a lot more contents to remember. You can certainly reinforce these by using memory aids such as flash cards but it's also useful to think logically. So have a look at the body and look at these regions and think what stick to the skin. If I'm looking at the body and I remove the skin, what am I going to see there, and that way you can logically determine what you're going to find.
So we're going to start with the left hypochondriac region which contains a portion of the stomach, the left kidney, the spleen, the tail of the pancreas, a portion of the left lobe of the liver, parts of the small intestines, the transverse colon and the descending colon whereas in the right hypochondriac region we have structures such as the right lobe of the liver and gallbladder, part of the duodenum, the hepatic colic flexure and the upper half of the right kidney.
Below the sternal region and flanked by the right and left hypochondriac regions, we have the epigastric region. This region contains the abdominal part of the esophagus, the pyloric part of the stomach, the spleen and the pancreas, part of the duodenum, part of the liver, the right and left suprarenal glands, part of the right and left kidneys, the ureters and part of the transverse colon.
Inferior to the epigastric region, we have the umbilical region which essentially encompasses the area surrounding the belly button. This region is bordered laterally by the left and right lumbar regions and inferiorly by the hypogastric region. It contains structures such as part of the stomach, the pancreas, the lower part of the duodenum, part of the jejunum and ileum, the cisterna chyli, the transverse colon, part of the kidneys and the ureters.
The next region of the abdomen we're going to look at is the lumbar region. Again, there's a left lumbar region and a right lumbar region and they're found on either side of the umbilical region. Because they're found on different sides of the body, again, these regions have different organs. So the left lumbar region contains the lower part of the left kidney, the descending colon and portions of the jejunum and ileum whereas the right lumbar region contains the tip of the right lobe of the liver, the gallbladder, the ascending colon, the lower part of the right kidney and parts of the duodenum.
If we move inferiorly, we can see this region highlighted in green which is the hypogastric region. It's also known as the suprapubic region because it's bordered inferiorly by the pubic bone. This region is found inferior to the umbilical region and is flanked on either side by the left and right inguinal regions. It can also be referred to as the hypogastrium which simply translates to "below the stomach". So all of these names give us a clue to where it's located. This region contains the ileum, the sigmoid colon, the rectum, the ureters and the urinary bladder when it's enlarged or filled with urine. Now because of the nature of the location of this region, there's going to be anatomical differences between the sexes. For example, the female hypogastric region contains the ovaries, the fallopian tubes and the uterus when it's enlarged whereas the male hypogastric region contains the vas deferens, the seminal vesicles and the prostate gland.
The final region of the abdomen is the inguinal region. Again, there's a left and right inguinal region and they're found on either side of the hypogastric region. The inguinal region is also known as the iliac region. So let's zoom in and have a closer look at the contents of these regions. The left inguinal region contains part of the small intestine, part of the descending colon, the sigmoid colon and the left ovary and left fallopian tube in the female pelvis whereas the right inguinal region contains structures such as the cecum, the appendix, the ascending colon, part of the small intestine and the right ovary and right fallopian tube. This region is also known as the inguinal region due to the fact that it contains the inguinal canal.
Before we bring our tutorial to a close, let's first summarize what we've learned today. So first we looked at the regions of the thorax including the infraclavicular region which is located inferior to the clavicle, the mammary region which contains the pectoral muscles and the breasts, and the inframammary region below it. We then looked at the sternal region which overlies the breast bone and finally, the lateral pectoral region.
We then moved on to the regions of the abdomen where we focused on the nine region scheme. First, we had the left and right hypochondriac regions which are found on either side of the epigastric region. Inferior to the epigastric region, we saw the umbilical region which is flanked on either side by the left and right lumbar region. Next, we had the hypogastric region which is situated between the left and right inguinal regions.
So that brings us to the end of our tutorial on the regions of the abdomen and thorax. I hope you enjoyed it and thank you for listening.