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Viscera of the abdominal cavity, bones and muscles of the abdominal wall.
Hello everyone! It's Megan from Kenhub here, and welcome to our tutorial about the cross-section at the level of the eleventh thoracic vertebra. In today's tutorial, we will be looking at any structures we can see at this level in the axial plane which is sometimes called the transverse plane or the cross-sectional plane. This plane passes through the body at a right angle to the long axis of the body dividing it into superior and inferior parts. The structures we will see today include organs, bones, muscles and blood vessels.
Knowing which structures you can see at this level in cross-section is especially important when looking at CT and MRI scans. They also come up commonly in exams. Just a reminder that when we look at cross-section CTs or MRIs, the patient is positioned lying on their back with the viewer positioned at the patient's feet looking superiorly towards the patient's head. Therefore, this side of the image is the right-hand side of the patient's body, this side is the left-hand side, this is anterior or the front of the body, and this is posterior where the back is. So, when we study cross-sections, always keep in mind that the right side of the screen corresponds to the left side of the body and the left side of the screen corresponds to the right side of the body.
So let's begin looking at the structures at the level of the eleventh thoracic vertebra. But before we do this, it's very useful to work out which level of the body we're at. Our section is going to be at the lower part of the thorax and at the upper part of the abdomen at the level of T11. So if we section the body at this level, we get a cross-section that looks like this. And in this cross-section, we can see the eleventh thoracic vertebra highlighted in green.
I'd also like to point out this icon here which will remain in the upper left hand corner throughout this video. It will act as a constant reminder that we are looking at a cross-section of the body at the level represented by this line which is of course T11.
Sometimes you might not always know the level of a cross-section and it's useful to know that a good way to estimate what level you are at is by looking at the vertebra. That is why it's important to know the structural differences between the cervical, thoracic and lumbar vertebrae. One important tip that’s good to remember is that the vertebral bodies get bigger as you move down the body.
So now let's have a look at the structures we can see in this cross-section starting with this structure here which is the diaphragm. As you should know, the diaphragm is a large musculotendinous structure that separates the thorax from the abdomen. It has three large openings at the level of the eighth, tenth and twelfth thoracic vertebra, therefore, we know that the diaphragm is definitely located at the level of T11.
Anteriorly, we can see the costal cartilages of ribs seven to twelve. As we can see in this cross-section, they're located on the right and left sides of the body. These costal cartilages are anterior extensions of the ribs. Only the seventh costal cartilage articulates directly with the sternum whereas the costal cartilages of the eighth, ninth and tenth ribs articulate with the sternum indirectly through the costal cartilage above. The eleventh and twelfth ribs float free at their anterior ends but they are not obvious in this image shown.
In between the costal cartilages is the end of the xiphoid process. In this cross-section, we can see the costal cartilages here and the xiphoid process between them. The xiphoid process is the most inferior part of the sternum and, unlike other parts, it does not articulate with any of the ribs.
The last bony structure that we can see at this level is the night rib. Looking at this illustration on the right, we can see that the ninth rib curves anteriorly downwards, therefore, it's not considered to be horizontal and that's why we can only see a small section of it here in the cross-section.
Now that we have gone over the body structures that we can see in this cross-section, let's move on to look at the muscles that we can see at the level of T11. On both sides of the body, we can see muscles that are located between the ribs. These are the external intercostal muscles. If we look at this image on the right, we can see that these muscles have fibers that pass obliquely downwards. These muscles are very important in forced inspiration.
Moving anteriorly, we can see this muscle here which is the rectus abdominis muscle commonly known by most people as the abs. If we look at this image on the right, we can see that this muscle extends from the pubic crest to the xiphoid process and the fifth to seventh costal cartilages. Posteriorly, there are few back muscles that we can see in this cross-section. This one highlighted in green is the latissimus dorsi muscle which we can see on both sides of the body. This muscle is commonly referred to as the lats and is a very broad muscle. Its name in Latin can be translated to mean the broadest muscle of the back. This muscle is responsible for many actions at the shoulder joint and the lumbar spine as well as assisting with respiration.
Next let's look at the longissimus thoracis muscle which we can see here on the right and left side highlighted in green. In this illustration on the right, we can see that this is a long muscle of the back inserting directly into the lumbar vertebrae before diverting outwards to span either side of the thoracic vertebrae. Finally, lateral to the longissimus thoracis muscle, we can see a muscle on either side of the body which is known as the iliocostalis lumborum muscle. This is a deep muscle of the back located laterally to the longissimus thoracis muscle. One thing I'd like to mention is that this muscle consists of lumbar and thoracic parts but in this cross-section we can only see the thoracic part of the muscle.
Now that we've identified all the muscles that we can see in this cross-section, let's move on to look at some of the organs. On the left of our cross-section which, remember, is the right side of the body, we can see the right lobe of the liver. This lobe is located in the right upper quadrant of the abdomen. Lying next to the right lobe is the left lobe of the liver. As we can see in this cross-section, the left lobe is much smaller than the right lobe. Another organ that we can see in this cross-section is the spleen. This organ is located on the right side of our cross-section which is the left-hand side of the body. As we can see in the image on the right, the spleen is located in the upper left quadrant of the body. The spleen plays an important role in both the hematological system and the immune system.
Anterior to the spleen, we can see the stomach. As you can see the outline is quite irregular and this is due to the presence of rugae which can be used to identify the stomach in cross-section. As the stomach curves downwards as well as forwards, we are able to see the pyloric part of the stomach which is also known as the pylorus. Here we can see that the pylorus is the most inferior part of the stomach. Posterior to the pylorus is the transverse colon. Notice the absence of rugae which can help you identify this as an intestinal structure rather than the stomach. The transverse colon is the largest and most superior part of the large intestine.
Moving posteriorly, we can also see the descending colon. In the cross-section, we can see that the descending colon is posterior to the transverse colon. This illustration shows that the descending colon is a continuation of the transverse colon. During the last part of this tutorial, we will look at some of the vessels that are visible in this cross-section. Highlighted in green is the abdominal aorta. This vessel is located anterior to the eleventh thoracic vertebra. It is the largest artery in the abdomen and is a continuation of the thoracic aorta. In this cross-section, we can also see the inferior vena cava. If you're struggling to tell the difference between the inferior vena cava and the abdominal aorta in a cross-section, it's good to remember that the inferior vena cava is found on the right of the abdominal aorta. So in our cross-section, it'll be located on the left.
The last structure we can see is the hepatic vein. On the right, we can see the hepatic vein located on the superior surface of the liver. This vein drains blood from the liver into the inferior vena cava
So that brings us to the end of our tutorial. Don't feel too disheartened if you found it quite hard to identify these structures in cross-section as it can be rather difficult. Just remember to keep practicing and try our quiz on this cross- section on our website. Identifying structures in cross-section is a great skill to have and can really help you read those CT and MRI scans.
Now that you just completed this video tutorial, then it’s time for you to continue your learning experience by testing and also applying your knowledge. There are three ways you can do so here at Kenhub. The first one is by clicking on our “start training” button, the second one is by browsing through our related articles library, and the third one is by checking out our atlas.
Now, good luck everyone, and I will see you next time.