0:00 In this video, we're going to talk about the spleen, the anatomy, and the 0:07 physiology. 0:08 Let's begin by looking at the anatomy. 0:10 So the spleen is below our diaphragm on the left side. 0:15 It's actually under our ribs, specifically between ribs 9 and 11. 0:20 The spleen is an intraperitoneum organ, not a retroperitoneal organ, and it 0:26 lies in the 0:27 left upper quadrant under the diaphragm. 0:32 So the tail of the pancreas also tickles the spleen, and here is our duodenum. 0:37 The left kidney is below the spleen. 0:40 The arterial supply of the spleen comes off the celiac trunk, which is off the 0:44 descending 0:44 aorta, specifically the spleenic branch of the celiac trunk, which is a tort 0:50 uous artery 0:51 that supplies the spleen and part of the stomach. 0:54 The drainage of the spleen is from the spleenic vein, which also drains part of 0:59 the pancreas, 1:00 and then joins into the inferior mesenteric artery before joining with the 1:05 superior mesenteric 1:06 artery, which then forms the portal vein. 1:09 And remember, the portal vein is what goes into the liver. 1:14 The esophagus comes off the diaphragm at the level of T10, meaning at the level 1:19 of the 1:20 10th vertebrae, and then the oesophagus joins to the stomach. 1:25 The stomach is not drawn here, but the stomach then joins with the duodenum, 1:29 which is the 1:30 first part of the small intestine we drew earlier. 1:33 And it's important to know that the stomach is in close proximity with the sp 1:38 leen. 1:38 So talking about the spleen now, well, whether vessels go in and out of the sp 1:43 leen is the 1:44 highlum of the spleen, the dimensions of the spleen, the spleen is about 5 1:50 inches high, 1:51 which is about 12 to 13 centimeters. 1:54 The spleen is about 3 inches in width, which is about 7 to 8 centimeters. 2:00 The thickness is about 1 inch, which is about 2.5 centimeters. 2:05 The spleen weighs about 7 ounces, which is about 200 grams, but this is on the 2:11 heavier 2:12 side. 2:14 Now, from all these numbers, we have odd numbers in inches and an ounce. 2:20 So we have thus, we can thus call the spleen the organ of odd numbers, 1, 3, 5, 2:28 7 and 9, 2:29 1, 3, 5 being the dimensions of the spleen in inches, 7, their weight in ounces 2:36 , and 2:37 the spleen over is under the ribs 9 to 11. 2:43 Now let's now cut a section of the spleen and look at the pathology, the hist 2:47 ology of 2:48 the spleen. 2:49 So here, the spleen is actually covered by capsule and it has to biculate 2:54 coming within 2:55 the tissues. 2:56 And here is the splenic artery, which is bringing blood into the spleen and it 3:02 branches off 3:04 into smaller arterios called central arterios. 3:09 They then continue on to become end arteries or end capillaries. 3:16 So they don't join straight away to veins. 3:19 Anyway, surrounding the arteries within the spleen are lymphoid tissues, lymph 3:25 atic tissues, 3:27 called the peri arterial lymphatic sheath or the peri capillary lymphatic she 3:33 ath. 3:33 Now, the peri arterial lymphatic sheath, they are a lymphoid organ. 3:38 They contain immune cells, mainly T cells and macrophages. 3:44 Surrounding the peri arterial lymphatic sheath is another lymphoid tissue 3:48 called the marginal 3:50 zone here in yellow. 3:52 So here in yellow is the marginal zone, which is made up of predominantly mac 3:59 rophages. 4:00 Now sort of within this lymphatic tissue are other lymphatic tissues or 4:06 clusters called 4:07 follicles here in green. 4:10 The follicles are essentially surrounded by the marginal zone and contain 4:14 immune cells 4:15 called B cells. 4:17 The peri arterial are lymphatic sheath, the marginal zone and the follicles 4:22 make up what 4:23 is known as the white pulp of the spleen. 4:27 The white pulp of the spleen make up 25% of the spleenic tissue and because 4:32 they contain 4:33 immune cells, they are thus important in fighting infections such as from 4:39 viruses. 4:40 They are important in mounting an immune response as well as producing 4:46 antibodies. 4:47 And we know this is so because if we remove the spleen of a person, the person 4:54 would have 4:56 lower amounts of antibodies in the blood and people without spleen are at an 5:01 increased 5:02 risk of infection. 5:05 Now going back to the spleenic artery now, when there is an artery there has to 5:11 be veins. 5:12 The spleenic artery as we know branches into the central arterial and then it 5:18 becomes end 5:19 arteries or end capillaries. 5:21 It doesn't actually connect straight away to veins to form veins. 5:25 These end arteries, they have no wall which allows the red blood cells and 5:29 other cells 5:30 to essentially flow into the surrounding tissue. 5:34 And essentially it is the surrounding tissue where it gets picked up. 5:39 The cells get picked up by a sinus system here in blue. 5:43 And the sinus systems are the venus sinus that we are talking about. 5:47 And they are all around the end arteries, all around the end capillaries here 5:52 in blue. 5:52 The venus sinus picks up these red blood cells and then transports them to the 5:56 collecting 5:57 veins. 5:58 And then the collecting veins will join up and drain it into the spleenic vein 6:03 before 6:04 leaving the spleen itself. 6:07 Between the end arteries and the venus sinus is an area of tissue called the 6:12 cords or also 6:13 known as the cords of bilroth. 6:15 And this is essentially where we have heaps of macrophages. 6:19 There are a lot of macrophages which are your eating cells, phagocytes within 6:24 the cords 6:25 of bilroth. 6:26 The cords and the venus sinus make up what is known as the red pulp. 6:30 The red pulp make up the majority of the spleen 75%. 6:36 The red pulp is important in destroying or filtering abnormal red blood cells, 6:41 just unhealthy 6:42 red blood cells as well as old red blood cells. 6:46 We know this because if we see the blood of someone with no spleen there is an 6:52 increased 6:53 number of abnormal red blood cells in the circulation. 6:56 For example there are red blood cells with howly jolly bodies which are 7:00 remnants of the 7:01 nucleus essentially. 7:04 So remember the spleen has a white and it has a red pulp. 7:08 Let us now look at the white pulp and learn about it in a bit more detail. 7:13 Let us zoom into this area here. 7:17 Here we have the central arterial branching and it will bring in the red blood 7:23 cell and 7:23 other things through the white pulp area. 7:27 Surrounding the archery remember is a peri arterial lymphatic sheath which are 7:31 predominantly 7:32 made up of T cells and macrophages. 7:36 Here we have a T cell. 7:39 Surrounding the peri arterial lymphatic sheath is a marginal zone in yellow 7:43 which are made 7:43 up of macrophages. 7:46 The follicles here in green is another lymphatic tissue which is surrounded by 7:51 the marginal 7:52 zone. 7:54 It also has a capillary entering the area. 7:58 The follicles are important and they contain B cells, naive B cells that have 8:04 not been 8:04 activated. 8:07 Again in the marginal zone you can find macrophages which are antigen 8:12 presenting cells. 8:13 Macrophages can be your typical normal macrophages or the special macrophages 8:18 called metallophilic 8:19 macrophages. 8:22 We don't have to go into detail on that. 8:26 Let's now look at an example of what the white pulp of the spleen actually does 8:32 . 8:32 So let's just say that coming from the peripheral tissues for example coming 8:36 from the skin a 8:37 dendritic cell will bring an antigen into the spleen. 8:43 The dendritic cell does this because the dendritic cell is an antigen 8:47 presenting cell and it 8:49 is responsible for activating the adaptive immune system. 8:54 It's important in activating T and B cells. 8:57 So the dendritic cell will bring the antigen and present it to the T cells in 9:01 the peri arterial 9:02 lymphatic sheath. 9:04 The presentation of the antigen to the T cells will activate the T cells. 9:09 When the T cells is activated it will then activate the B cells in the follicle 9:15 . 9:15 The activated B cell can then become what's known as a plasma cell either in 9:20 the red pulp 9:21 or in the white pulp. 9:23 The plasma cells are cells which actually produce antibodies. 9:28 Upon activation the B cells can produce a lot of antibodies against that 9:33 antigen that was 9:35 presented in the first place. 9:37 The antibodies can be IgG antibodies which are the main blood antibodies or it 9:43 can be IgM 9:44 antibodies which are your initial antibodies produced. 9:51 Another story could be for white pulp function could be that a pathogen such as 9:57 a virus can 9:58 enter the spleen by itself. 10:00 The virus gets in contact with the naive B cells in the follicle. 10:05 The B cells can pick this up and then it will present it to the nearby T cell 10:10 and through 10:11 what is known as co-stimulation the B and T cell activate each other. 10:18 So the activated B cell can then become a plasma cell again and then produce 10:22 antibodies 10:23 against that specific virus. 10:27 Another way for mounting an immune response is where the macrophages itself 10:31 within the 10:31 spleen picks up these pathogens such as viral antigens. 10:37 It then presents the antigen to the T cells and then the T cells will activate 10:41 the B cells 10:42 in the follicles. 10:44 The B the activated B cells can then become plasma cells and then the plasma 10:48 cells can 10:48 produce antibodies against that antigen. 10:52 So as you can see the white pulp it is very important in mounting an immune 10:57 response and 10:58 also producing antibodies against infections or against other things. 11:03 Now let's talk about the red pulp which make up 75% of the spleen tissue. 11:09 Remember the red pulp is responsible for destroying or filtering old abnormal 11:14 red blood cells. 11:17 Let's zoom into this area where the venous sinus and an arteries connect. 11:23 So coming from the central arterial you have the branches of the central arter 11:28 ial and you 11:29 essentially have the terminal capillary or the end artery. 11:33 It brings red blood cells and many other cells into the red pulp area. 11:38 The red pulp is made up of an area called the cords which are filled with mac 11:44 rophages. 11:45 The macrophages surrounding the cords is also surrounding the venous sinus 11:51 itself. 11:52 I apologize for the graphics of the video it became bad but hopefully you guys 11:57 can still 11:57 make up the drawing and what I'm saying. 12:00 So the red pulp of the spleen again is made up of the cords and the venous sin 12:06 us. 12:07 As you can see here there are slits between endothelial cells of the venous sin 12:13 us and 12:13 these slits are important in filtering red blood cells. 12:18 When red blood cells move into the venous sinus they are drained into the 12:24 collecting veins 12:25 before draining into the spleenic vein. 12:28 So for example here we have red blood cells and they are moving into the cords 12:34 and then 12:35 they will try to enter the venous sinus through the slits. 12:46 Old abnormal red blood cells are unable to pass through the slit effectively 12:51 and thus 12:52 are phagocytized by the surrounding macrophages. 12:55 This is because the red blood cell is too slow or just unable to get through 13:00 the slit 13:00 because they have an abnormal shape for example. 13:03 And so this is the mechanism by which the spleen filters or destroys red blood 13:11 cells. 13:12 Viruses as well as other pathogens can also be captured by the macrophages in 13:16 the red 13:17 pulp and then be presented to the cells of the white pulp also. 13:22 Finally, opsonized pathogens or opsonized red blood cells which are basically 13:28 pathogens 13:29 or red blood cells that are tagged marked by the body are able to get destroyed 13:33 by macrophages 13:35 in this area. 13:37 So as you can see by all the examples I have given the red pulp of the spleen 13:40 is important 13:41 in clearing out old damaged red blood cells as well as pathogens. 13:46 The final important role of the spleen aside from being a white pulp and being 13:51 a red pulp 13:52 is sequestration of platelets. 13:55 Platelets are also known as thrombocytes and they are circulating factors which 13:59 are 13:59 important in coagulation and forming plots. 14:03 One third of platelets are actually sequestered or stay in the spleen. 14:10 And so the spleen is actually important in maintaining good levels of platelets 14:15 in circulation. 14:16 I hope you enjoyed this video on spleen anatomy and physiology. 14:19 Thank you for watching.
