chapter 20 I need you to know the functions of the lymphatic system maybe which you already know you already know that that thanks to the lymphatic system I'm on it's light too by the way we are constantly draining interstitial fluid and therefore are not as likely to suffer from edema that we'll talk about how that that can be facilitated and also not facilitated on another slide we already know that really same same point here because the bathtub is always being drained the lymphatic system allows us to treat hydrostatic pressure of interstitial fluid about zero millimeters of mercury you may or you know that that especially your lymph nodes and spleen are are responsible for filtering debris and potentially pathogens from lymph and therefore really help to clean the body you hopefully already know that the spleen for instance functions in not just recycling red blood cells that are old and damaged and helping us to reclaim the good stuff that's within red blood cells like amino acids and iron but that the spleen in incident to the liver helps to store that iron we've talked about the spleen as the recycling center but it also helps to store red blood cells white blood cells and therefore this point has two major portions and we'll come back to this but we might as well preview white and red pulp and the red of pulp is the portion that's primarily concerned with the recycling of old slash damaged red blood cells the white pulp is the portion that's responsible for offering housing and storage look out for white blood cells for leukocytes the lymphatic system in generals are not just spleen but also lymph nodes and smaller clusters of lymphoid tissue such as nodules offer surveillance surveillance locations kind of like lifeguard stands for our lymphocytes and macrophages offer locales for our lymphocytes and macrophages to become activated to sort of realize their destiny and also to allow housing space for lymphocytes especially to proliferate to to give rise to a matchy-matchy army and then the part of the the lymphoid or lymphatic function that you're probably not aware of is that yes we absorb nutrients across the wall of our small intestine and though of those nutrient monomers are are sent directly into the circulatory system the exception is lipids the nutrient monomers that we derived from lipid digestion actually get sent first into the lymphatic system and only later as you may recall near the collar bones and the collar bones are shared or relayed to the circulatory system so that's kind of it's kind of surprising probably that the lymphatic system is responsible for absorption at least directly of lipids from the small intestine okay I'm moving to slide 3 slide 3 you actually already have studied we looked at this this very diagram in the blood chapter early on as a preview and the the image next to it is just zooming way and so that we can drive home the idea that plasma leaks and gives rise to interstitial fluid interstitial fluid enters the lymphatic system and is instantaneously referred to as limp so this is a nice nice image that really helps to drive that idea home moving on to slide 4 this is actually a review you know most of this we just talked about an obsessional fluid giving rise to lymph but plasma giving rise to interstitial fluid we already know that our capillary beds sort of fail to reclaim about three liters of interstitial fluid per day and and therefore we're generating about three liters of lymph every day and you hopefully already know that lymphatic system is a network of vessels and primarily lymph nodes with lots and lots of other organs and structures sort of helping contribute to all of the lymphatics functions that we went over in inside - anywho one thing that you might not realize is that the lymphatic system because lymphatic capillaries are blind and the lymphatic system carries carries lymph in only one direction so it's it's generated at those sort of coldest act like lymphatic capillaries and then it's delivered ultimately to those those ducts those lymphatic vessels are especially large in the air I start our clavicles so it's a one-way trip in other words lymph does not circulate it's made anew constantly which is one of many contrasts between the lymphatic system in a circulatory system okay I'm now looking at slide five slide five hopefully you realize that that circulatory or blood capillaries and lymphatic capillaries are likely in proximity to each other otherwise how are we going to facilitate the uptake of lost fluid so close close proximity or proximal you could say there are a few places where the lymphatic system is missing but for the most part it's it's throughout the body and you can get a sense of where the lymphatic system is which is really everywhere and by looking at the partial image on slide 2 as well as the image on slide 9 which I think gets repeated yeah again on on subsequent slides I'm so really really spread out just about just about everywhere very similar to the circulatory system in that sense very Network like and one difference between the circulatory system in the lymphatic system is that our circulatory system is especially our capillaries a circulatory or blood capillaries they feature intercellular class as you know and intercellular class are certainly helpful in allowing capillaries blood capillaries to leak but believe it or not lymphatic capillaries are even more leaky they're even more leaky and one of the reasons why there's even more leaky is that they're there the cells that make up the lymphatic capillary walls the endothelial cells they overlap really loosely and therefore create many many many many many mini valves if mini valves are not the same thing as valves okay and mini valves are really loose really loose and they are forced open with greater pressure hydrostatic pressure of interstitial fluid so the the more interstitial fluid there is the more mini valves open and the less interstitial fluid there is the less mini valves are forced okay okay having really leaky or very permeable lymphatic capillaries it's a good thing we we want that interstitial fluid and and virtually all of its contents to enter the lymphatic system but also be aware that that mini valves are so permeable that even some whole body pathogens can enter lymphatic capillaries cancerous cells can enter if they're small enough or rather they're clumped into small enough groups can enter many valves so having a lymphatic system is risky in the sense that it offers a free way that's readily accessible by bad guys and that's one of the reasons why the lymphatic highway if you will is interrupted very very frequently by lymph nodes lymph nodes act as filters clearing away checking for filtering constantly debris and hopefully those bad guys I'm on slide six and I'm looking at the sort of origin or beginning of a lymphatic capillary where we can really see okay here's an endothelial cell and here's its neighbor and they overlap that overlap overlap is called a mini valve so in this particular image we can see or many valves very very loose loose I'm on slide 7 you do need to know that lymphatic capillaries that that reach into the core of our villi which are these finger-like projections into the lumen of our small intestine villi each one is eight okay then at the core of each villus there's a lymphatic capillary that's primarily responsible for a lipid absorption and because it's specialized for this for this particular function it has a special name it's a lacteal lacteals our lymphatic capillaries but they're specifically lymphatic capillaries that are that are serving the absorption of lipids from the small intestine I'm on slide 8 and this quarter because we're so crunched for time I'm not actually going to have you learn sort of the different levels of vessels to the degree that I would I would typically have my students learn but I do want you to know that lymphatic vessels future valves valves are much more internal whereas mini valves are part of the actual wall and mini valves are a lymphatic capillary only thing whereas larger lymphatic vessels aren't gonna have me valves but they will still have valves okay we're going to move to slide 9 no one panic ducts there are two of them these are the largest lymphatic vessels and these are the ones that dump lymph now clean now filtered back into the circulatory system so that this excuse me so that the circulatory system isn't really ultimately losing Florida it gets that that fluid back and then the particulars of those Doc's I'm actually gonna skip them this quarter which makes me a little bit sad okay just two major lymphatic ducts okay dumping back into our circulatory system and actually the way that I just circled these is a little misleading so let me let me undo that this is the sort of feed back into the circulatory system the green here whereas the blue is the circulatory system that's receiving that that now cleansed lymph so don't worry about these labels okay don't worry about these labels for exam two however please be aware that you will need to know veins including some of those that are shown and and arteries for that matter for the practicum / the practicum study go in you I'm on slide 11 the lymphatic system doesn't have a pump all right it doesn't have the dedicated pump that we see in the circulatory system our heart and so it's going to rely on [Music] well neighbors and friends it's going to rely on muscular pumping of skeletal muscle it's going to rely on muscular pumping of smooth muscle in adjacent arteries thank goodness we have the mechanism of vowels in our lymphatic vessels to prevent lymph from flowing backward we also rely on the respiratory pump or skeletal smooth and rest or milking yay to help move along and then there is is also some smooth muscle in the walls of our lymphatic vessels not so much our lymphatic capillaries but our larger lymphatic vessels and that they also helps lymph to to move along but if if a patient is ever in mobile for for any length of time there's there's always a risk or these these mechanisms really not being able to fight gravity and there's always a risk of edema or swelling so it makes it really really clear that physical activity is is so important in part because of the skeletal muscle pump to get the lymph to move along move along move along I'm on me speaking of a long I'm on slide 12 hey don't don't worry about these labels no no freaking out okay hopefully you already realized because we talked about functions the lymphoid tissue especially the lymphoid tissue we see in lymph nodes in nodules in the spleen and so the other regions where we can find lymphoid tissue is is providing housing surveillance sites maturation sites proliferation sites for lymphocytes and macrophages the lymphocytes and macrophages and in terms of the what lymphoid tissue looks like I just want to know what kind of tissue a kind of tissue because chances are you learned loose reticular connective tissue well enough in 2:41 to already recognize they've got oodles and boodles of nooks and crannies that it looks sort of like an English muffin and all of those nooks and crannies are what provides storage space and surveillance space and space for proliferation where lymphocytes and macrophages are concerned okay so Lois reticular connective tissue in just in case okay moving on to slide 13 I'm a little bit worried because my husband just walked in the house so you might interrupt us I'm going to just interrupt to begin with sorry for the interruption on slide 13 and then because this this quarter is so well such a mess we're gonna we're gonna not worry about these these structural categories at least not in a formal way but but please realize that that some lymphoid tissue is clumped together and and therefore makes conspicuous organs they might be small but they're conspicuous organs whereas some lymphoid tissue is more sheet blank and more more so infused and less clumped together and therefore not not as conspicuous and one of the reasons why we see that is because a lot of our our lymphoid tissue is sheet-like and inconspicuous and imbued into our mucosae and that's actually what molt stands for molt mucosae associated lymphoid tissue okay a lot of this is very sheet-like and inconspicuous sometimes malt is clustered and when it is clustered it helps to make up little clumps little clumps in say our appendix and our peyer's patches and I'm going to move to the next slide slide 14 peyer's patches are a little little clumps or nodules of lymphoid tissue that are housed just within the distal portion of our small intestine okay and then we also have a sort of clumped lymphoid tissue in our in our appendix all right and then some of the other things that we're looking at in this image well we'll actually use a different slide to point out so here we go slide 15 now if there's really only one thing that you learn from this chapter this is probably it this slide 15 is side 16 are probably most important because we're going to need to recognize the phrase primary and secondary lymphoid organs in the immune chapter so we don't master these terms in the lymphatic chapter we're going to be cute boy I wonder what word I was trying to just try we're gonna be poached for a subsequent chapter and nobody so we need to know that the primary lymphoid organs are specifically the thymus and red bone marrow and what makes a lymphoid organ primary is that this is where B cells and T cells mature mature this isn't necessarily where they become activated you know in fact we hope it isn't where they become activated and activated and maturity are not the same thing which will we'll come back to in the immunity chapter but maturity means old enough to do their to do their job whereas activation means hired okay so just because you I don't know graduate from high school you're you're mature enough to get a job but that doesn't guarantee that you're getting hired anywhere we'll come back to that and then secondary lymphoid organs include lymph nodes the spleen the tonsils which are yet another example of sort of clumped lymphoid tissue peyer's patches the appendix and then it and then just in general malt mucosa associated lymphoid tissue okay and what makes only point organ a secondary lymphoid organ is that this is where this is where lymphocytes don't mature rather they they get hired here and they get activated become activated okay and then if you're very visual like me slide 16 will actually help you probably more so to not just figure out who are the primary lymphoid organs who are the secondary lymphoid organs but I shall also visualize where they are in the body which could be important for exam 2 could also be important for the practicum okay so red bone marrow and thymus are primary lymphoid organs okay tonsils are secondary lymph nodes which aren't shown here but we have seen them on in different images in this lecture our our secondary spleen is secondary peyer's patches secondary and appendix secondary okay so that means that red bone marrow and thymus this is where lymphocytes b-cells and t-cells go to mature whereas they've notes tonsils spleen peyer's patches molds for that better we should add that to our list by the way the appendix this is where lymphocytes you know to become activated okay okay lymph nodes we have hundreds hundreds spread out throughout our bodies and the number varies and in fact estimates vary I've heard as low as 300 I've heard as high as 700 maybe a rough average would be 500 ish but you have hundreds of lymph nodes and they are your chief secondary lymphoid organs so more often than not if a lymphocyte is becoming activated it's in a lymph node and how does it become activated by meeting it's matchy-matchy antigen okay that's what activation means meeting it's at matchy-matchy antigen most of your lymph nodes are are fairly deep within your body and so you're not likely to feel their shape you're not likely to note when they're swollen but you do have six of those hundreds of lymph nodes then over the course of your lifetime you're likely to become aware of you have to and your neck that are especially superficial as they're called cervical you have to in your armpits one permit that are especially superficial okay you have more than two in your neck you have more than two in your armpit I'm saying you have two there especially superficial in your neck two that are especially superficial in your armpits and then two there especially superficial in the groin and those that are in the armpits are called axillary those that are in the groin inguinal okay now all we're saying is it's these six that are especially superficial and that means that when you have a respiratory infection or a sinus infection because these guys are nearest your sore throat your stuffy nose your angry cranial sinuses these guys if they're very close to the surface and they are there are likely to swell and you're likely to actually feel them if you have an infection in an arm or an infection in your upper torso these guys actually are especially superficial you're especially likely to feel when they're swollen and tender if you have an infection in your groin an infection in the leg in the hip these guys are especially likely to be noted notable just because they're so superficial there's swelling is likely to be something that you you detect but please do not conclude that you have only six lymph nodes that is ridiculous moving on 18:18 we've actually already established that lymph nodes act as filters there we're moving debris they're removing potential pathogens okay and and therefore cleaning wimps which is kind of like cleaning blood however realized that the lymphatic system picks up the interstitial fluid all on almost its entire length so it's not like it's it's only working on fluid that it gleaned distally okay moving on to 19 your lymph nodes are somewhat being shaped they have a fibrous capsule as so many of your ovoid organs do okay and they have lots of sinuses however this quarter we're gonna really dumb this down just because the core is nutty not because I think you're dumb I think you're brilliant I want you to know I'm on 20 now I want you to know that each we've done has a cortex each one's node has a module ah okay I want you to know that the cortex has lots of follicles here's a follicle there's a follicle there's a follicle and these follicles act as germinal centers and whenever we see a germinal center whether it's in a lymph node or not this is an area where b-cells in particular are proliferating like mad so we make b-cell armies in the cortex of our lymph nodes okay but also in our cortex we will see t-cells going about their roaming business they roam okay in the medulla we can find b-cells and t-cells and we'll find out later that plasma cell is just a further differentiated lymphocyte but the tango message is what am I expecting to find in a lymph node well B cells T cells macrophages and possibly bad guys okay follicle that's what I care about this this layer cortex that's what I care about this core medulla that's what I care about I want you to know that there's a fibrous capsule but we're not gonna bother with these partitions here that are called trabeculae they're just like invaginations of fibrous capsule but we're not going to bother with those this quarter we're also not going to bother with medullary cord art is breaking a little bit but oh well we're also not going to bother to learn the different sinuses what they're called where they are in the lymphatic or in the lymph node rather this quarter and that means that that we're gonna we're gonna really dumb this list down we're gonna really simplify that list in just a hot second what I what I want you to know is that because you know we've no time on 22 by the way I don't know if I told you that I've moved on what a jerk if a lymph node is being shaped okay that means that it has a concave side here and a convex side here okay and often when an organ whether it's a lift out or otherwise has this this being shape a concave side and a convex side the concave side I'm making a mess here so you clean this up a little bit the concave side well will act as a hill um hilum and sort of be like a lawyer or an entryway or an exit way mudroom if you will for circulatory vessels and in this case lymph at vessels as well okay so it's kind of like an access point all right and where lymph nodes are concerned we're going to move on to a slide 23 by the way live live is always entering on that convex on that convex surface and it's always exiting from that concave surface LM here okay and notice that there are fewer vessels leaving here leaving the lymph node then there are vessels entering the lymph node side 23 okay what does this mean well it means that lymph that's arriving on the convex side of the lymph node is forced to slow down as it's moving through the lymph node it's forced to slow down because there are fewer vessels on the concave side there just er there are fewer ways to get out okay and if Memphis is forced to slow down on its way through a lymph node then leukocytes macrophages and lymphocytes have more time to practice their function of surveillance okay so here's the gist lymphatic vessels arriving to our convex side apparent lymphatic vessels we're not gonna worry about sinuses this corner okay but these guys they're they're sending limp into cortex through medulla and ultimately out oh I actually erased a little too much there let's back up a little synergy I hope there we go getting rid of sinuses getting rid of sizes okay cortex medulla and then out from efferent efferent lymphatic vessels at the hilum meaning meaning the concave side where does these guys our comeback site okay that's not order I need you to know and really why right okay so 24 24 the only the only thing is we're gonna worry about again fibrous capsule okay and then these guys follicles where our follicles and then I'm not seeing any follicles here why because this is medulla that's it yes so logically that's all I'm gonna worry about this order okay I'm on 25 your spleen if you do not know that by the time the corner ends then you really should not graduate to 42 and it's very very high in the abdomen in fact it is touching the diaphragm it's about diaphragm okay it too is being shaped so it has its own hilum as well it too has a fibrous capsule okay but but what I want you to know you actually you already know you already know that the spleen features white pulp and red pulp I'm moving to 25 there's a diaphragm in in contact with the spleen our spleen this is kind of wrong or being shaped but please know that the pig has a really elongate almost more shaped display one of the few differences between the fetal pig and the human body okay so here's this plane hugged by diaphragm very very left even further left than your stomach okay okay I'm on 27 the spleen acts as lymphoid tissue and so it offers leukocytes surveillance positions room to mature room to proliferate and acts as recycling plant we already know that for not just old and or damaged red blood cells but also for platelets old and/or deranged platelets excuse me we already know that the spleen stores iron for instance with the aid of the liver we maybe did not know for that your spleen stores excess platelets that are there healthy stores kind of a back stock of monocytes just to kind of keep us ready for when they might be needed and it's it's thought that spleen and liver may be the site for erythropoiesis or may be a site for for erythropoiesis in in a fetus and a fetus so that the red bone marrow maybe sort of supplemented by efforts of the spleen and the liver that's a maybe okay I'm not gonna worry about histology I'm on slide 28 I just need to know that this beam has red pulp and white ball I don't really care whether or not you can find because frankly one is red and one is white okay but you should know that the red pulp is is responsible for sort of the recycling function that the spleen provides and the white pulp is more of an immune area so it's gonna offer those surveillance points and in that sense sort of act like a lymph node and it's also gonna act as as a storage site for for instance monocytes okay moving on I'm on 29 moat where he talked about mult multi thin and inconspicuous and sheet like throughout our mucous membranes but sometimes it's it's clumped and when it's clumped it helps make up our tonsils so you have four tonsils our peyer's patches nobody wants to count how many peyer's patches you have and your appendix you have one appendix okay tonsils four tonsils and in this image you you can't really tell that you have four you can only only see the three sort of flavors of tonsils this tonsil is a loner it's a singleton okay and it's called your pharyngeal tonsil this tonsil is paired so you have right and left Palatine tonsils okay and this tonsil is a singleton is not paired it's called your lingual your lingual tonsil okay and tonsils are are small clumps of lymphoid tissue and they do have journal centers they do offer small surveillance sites for lymphocytes okay I'm on 31 and I'm not learning too much whereas on 32 you you can better see oh yeah there's one Ferengi tonsil there's one lingual tonsil but there's a left and a right Palatine tonsil okay and then other clumps of moles of lymphoid tissue peyer's patches again distal small intestine that's these guys no you do not have exactly four and then the appendix there's just one okay the appendix is a little dingle-dangle a little sac almost that's sort of hanging off the very very very first portion of the large intestine that just after the small intestine dumps into large intestine that's where you can find the appendix but we'll get more specific when we get to the digestive system so more later okay both peyer's patches and the appendix because of where they're located they help prevent bacteria which is helpful or maybe helpful in our gut from from infiltrating deeper with everybody from from breaching the wall of the intestine okay and moving on on 33 the thymus we actually already studied of it we already know that this is where T cells in particular mature so not only a primary lymphoid organ but specifically primary primary for T cells okay we already know that the thymus atrophies as we age it becomes smaller and smaller and smaller and then I'm not going to worry about these particulars this corner I think we've already seen the image on 34 in the past right large conspicuous thymus and newborn where the hell is it in an adult okay and then slide 35 is one of the more important slides on this in this lecture please please please do yourself a favor and complete the table and then and then clear it out take everything off of it and make it again and clear it out and make it again okay so table very important otherwise why did I bother to make it okay thanks