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Hello, everyone! This is Joao from Kenhub, and welcome to another anatomy tutorial where, this time, I'm going to be talking about none other than the spleen. And to do so, I’m going to be essentia... Read more
Hello, everyone! This is Joao from Kenhub, and welcome to another anatomy tutorial where, this time, I'm going to be talking about none other than the spleen. And to do so, I’m going to be essentially exploring these two images that you see here on the screen. So, on the left side, we’re looking at the diaphragmatic surface of the spleen and here we see then on the right side, the visceral surface of the spleen.
The spleen happens to be a forgotten, one of those forgotten, organs that sometimes you ask what is, what does it do, and here right now, we have the highlighted spleen from an anterior view of the abdomen where you see a little bit of the liver here retracted, and the pancreas, a little bit of the colon, and we just have a few cuts here because we just removed a few structures so we can then expose the spleen.
So, what is exactly the spleen and what does it do? It is the largest immunological organ of your body and measures about 12 centimeters in length and weighing approximately 150 grams; however, this weight may vary from individual to individual. The spleen is a highly vascularized organ and is purple in color. It lies intraperitoneally in the left hypochondriac region between the ninth and twelfth ribs just inferior to the diaphragm which we also see a little bit here on this image – the diaphragm. This organ is surrounded by a layer of fibroelastic tissue and its main functions are associated to immune responses in our body, synthesis of antibodies, filtration of blood, lymphopoiesis, and phagocytosis.
Now, in order to help you remember the macroscopic anatomy of the spleen, I have here a few helpful hints. The spleen has two borders – a superior and an inferior one –, two extremities – an anterior and a posterior extremity –, and two surfaces that I showed you before and we have here the images – a visceral one and a diaphragmatic surface.
So, let’s begin by looking at the borders of the spleen starting with the superior border which you see here highlighted on both of these images. The superior border of this organ also known as the upper margin of the spleen, forms the border between the gastric and diaphragmatic surfaces. There is also this margin here that you see now highlighted which is then the inferior margin of the spleen. It’s also known as the lower margin. It’s the border between the diaphragmatic and visceral surfaces.
Now, let’s take a look at the two extremities of the spleen starting with this one that you now see highlighted, this is then the anterior extremity of the spleen. The anterior extremity of the spleen is basically the most anterior part of this organ seen here highlighted. The other extremity which is in this portion we see here highlighted is known as the posterior extremity of the spleen and it is the posterior most end of this organ which is of course known – and we name it – the posterior extremity.
Let’s take a look now at the surfaces of the spleen starting with the diaphragmatic surface. Now, what we have here on this image is a cross-section of the spleen done at the hilum of the spleen which is found right about here. And you can see on both of these images highlighted in green, the diaphragmatic surface of the spleen. Now, as you can see, it is a convex surface facing the diaphragm. Now, this smooth surface is directed upwards and is in relation with the undersurface of the diaphragm.
The next part of the spleen that I’m going to be highlighting here is known as the gastric surface of the spleen, which is then found on the visceral surface of the spleen. And the visceral surface of the spleen, it can be divided into three sub-surfaces. One of them that we’re looking right now is the gastric surface of the spleen. Now, as the name indicates, this is the portion of the spleen that is in direct contact with the posterior wall of the stomach. This is a broad concave surface which is directed upward, lightly forward and towards the middle and it is then one of the three concave visceral surfaces of the spleen.
The next visceral surface is the colic surface of the spleen seen here highlighted in green – wow, this even rhymes, spleen and green – I think this is gonna happen throughout the tutorial. Now, this surface is contact with the colon. The spleen sits upon the left colic flexure or the splenic flexure which is the curvature between the transverse colon and the descending colon.
The third visceral surface of the spleen we will look at is the renal surface of the spleen which is seen on both of these images highlighted in green. It is the lower surface of the spleen that is related to the upper part of the anterior surface of the left kidney.
Now, so far, we have looked at the borders, extremities and surfaces of the spleen. Now, let’s see how this organ is suspended in the retroperitoneal space. The spleen is surrounded by the peritoneum, and the foldings of the peritoneum form two ligaments – two very important ligaments. One of these being the gastrosplenic ligament seen here highlighted in green. The gastrosplenic ligament stretches between the greater curvature of the stomach to the hilum of the spleen which is this area here where all these vessels are found. The other ligament formed by the folding of the peritoneum is the splenorenal ligament. This ligament connects the left kidney with the spleen also at the hilum of the spleen.
In addition to the peritoneum, the spleen is also covered by a fibroelastic connective tissue known as the fibrous splenic capsule. So, as I just said, this is a fibroelastic connective tissue. Because the spleen is a very soft organ, this fibrous capsule helps the spleen maintain a relatively constant external shape.
The next structure of the spleen we will look at here is known as the hilum or the splenic hilum as I mentioned before. It is the entry and exit site of the splenic vessels located between the gastric and renal surfaces of the spleen. Now, as I mentioned earlier here, we also find the gastrosplenic and splenorenal ligaments as you remember well when we look at the structures. And please note that this part of the spleen is not covered by fibrous splenic capsule or the peritoneum.
As we saw on the previous slide, the blood vessels of the spleen just pass through the splenic hilum. One very important vessel that passes through the hilum and supplies oxygenated blood to the spleen is this one that we see here highlighted in green on both of these images. It is the splenic artery. And as I said, this supplies oxygenated blood to the spleen and this artery is the third branch of the celiac trunk as well as being the largest branch and it reaches the splenic hilum by passing through the splenorenal ligament. The splenic artery then divides into about six branches which enter the spleen at the hilum.
The next structure we’re going to be seeing here highlighted is then a vein, this is the splenic vein arising from the hilum and drains venous blood from the segmental splenic veins. It courses behind the pancreatic body joining the superior mesenteric vein towards the hepatic portal vein.
The next structure we’re going to be highlighting here is known as the splenic pulp. From a structural point of view, the spleen is comprised of the splenic pulp and the trabeculae of the spleen. Now, the splenic pulp is a mesh of fine reticular connective tissue that is found between the trabeculae of the spleen. There are two types of splenic pulp. The red pulp which gives the spleen its soft, spongy consistency and it is comprised of splenic sinuses engorged with blood. There’s also splenic cords, and a marginal zone that borders the white pulp. The function of the red pulp is to act as a mechanical filtration of red blood cells clearing out defective as well as aging erythrocytes.
The other type of splenic pulp is the white pulp. This one contains aggregations of lymphocytes varying in size that are known as the splenic nodules or malpighian corpuscles or bodies. These malpighian corpuscles are composed of B-lymphocyte rich lymphoid follicles and T-lymphocyte rich periarteriolar lymphoid sheaths also known as PALS. The function of the white pulp is to facilitate an active immune response through the humoral- and cell-mediated pathways.
The next structure we’re going to be highlighting here is known as the trabeculae of the spleen. These are connective tissue partitions that extend from the hilum and fibrous capsule penetrating into the spleen and dividing the splenic tissue into small chambers. Now, these small chambers contain blood vessels which are the trabecular arteries and veins, which happen to be the next topic that we’re going to or the next structures we’re going to be highlighting here in green. All these dots are showing then the trabecular arteries which are small branches of the splenic arteries and are transmitted through the splenic pulp. They are ensheathed by the lymphatic aggregations of white pulp. Now, these vessels are extremely ramified – so a lot of branches.
The other structures that we see here in blue but now we’re changing them or highlighting into green are the trabecular veins. So, they are also seen here in the pulp of the spleen and receive deoxygenated blood from the pulp veins. They drain into the splenic vein which in turn drains into the hepatic portal vein.
Before we conclude this tutorial, I would like to add a few clinical notes. To be more specific, I will add the two most common clinical points related to the spleen. These include then splenomegaly which is the enlargement of the spleen due to hematological disease and also rupture of the spleen due to trauma. While the spleen is not a vital organ which means that its functions are not useful for you to be alive. So, the treatment for both of these conditions is then complete removal or procedure which we call then splenectomy. Untreated damage to the spleen can quickly lead to massive internal hemorrhage and eventual death.
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.