Immune and Lymphatic System (Nursing)

00:01 Now let's take a look at the anatomy of the Immune and Lymphatic System.

00:08 The bone marrow, in addition to having a hematologic role also makes white blood cells.

00:13 So it's actually the starting point in a lot of ways of the immune system as well.

00:18 There's also another structure that's in some ways a temporary structure called the thymus that has a very important role in the maturation of immune cells.

00:29 We also have the spleen, which already serves a hematologic role, but also has a smaller role in immune defense.

00:37 We also have various lymph nodes scattered throughout the body, such as the cervical lymph nodes or the axillary lymph nodes in the armpit, inguinal lymph nodes down in the pelvic area.

00:49 We also have lymph nodes, or types of lymph nodes in internal organs such as the small intestine called Peyer's patches.

00:58 We have intestinal lymph nodes scattered throughout the mesentery.

01:03 And we have lymphatic drainage that's going to be draining these areas that form a very large thing called the cisterna chyle and the thoracic duct.

01:15 We also have other sorts of immune defense in the oral pharyngeal area, we have pharyngeal tonsils, we have palatine tonsils, we have tonsils on the tongue called lingual tonsils.

01:29 So that's a very widespread area of immune defense.

01:35 The cells involved in that immune defense vary quite a bit as well.

01:39 And we've mentioned this already in the hematologic section, we have basophils and eosinophils that are involved in allergic responses, but also parasite defense.

01:49 We have macrophages, which can eat up and ingests various organisms as well as foreign debris.

01:58 We have neutrophils to fight bacteria and fungi and we have lymphocytes to fight viruses.

02:05 Looking at the lymphocytes a little bit more closely, we see that we can have B lymphocytes and T lymphocytes.

02:12 Now, B lymphocytes are both made in and mature in the bone marrow.

02:18 T lymphocytes, on the other hand, are made in the bone marrow, but they actually mature in a different organ called the thymus hence the name T lymphocytes.

02:30 Now, the thymus is something we haven't seen before.

02:32 And there's a reason for that, that we'll get to.

02:36 But the thymus is going to be related to the sternum.

02:41 And it's going to be sitting just deep to the sternum, and superficial to the wrapping of the heart that we call the pericardium.

02:49 So it's going to sit in the anterior most portion of the space between the lungs called the mediastinum.

02:58 Now, the thymus itself is very much involved in the maturation of T cells.

03:06 Now, the process of T cell maturation can be pretty complicated.

03:10 Again, these precursor cells like all these other immune cells, it really made in the bone marrow, but they're not ready for action yet.

03:17 So through the circulation, they reach the thymus, and they undergo further development.

03:24 So what happens is the developing T cells in order to be any good to the body have to recognize the what's called MHC molecules on the surface of cells.

03:37 So these are something called major histocompatibility complex markers.

03:42 And they're basically what tell T cells to attach to them and do their job.

03:47 So what the thymus does is expose these potential T cells to various forms of MHC.

03:55 And they have to recognize some form in order to be selected to move on.

04:01 That's something called positive selection.

04:03 Because if it doesn't recognize MHC, there's no point in having it circulate.

04:07 So we'll just be removed from the whole process and eaten up by macrophages.

04:13 But you also want to make sure that T cells don't attach too strongly to self antigens, because you don't want T cells to attack the body that would be basically an autoimmune disease.

04:26 So the thymus is also exposing these potential T cells to various self antigens.

04:33 And in this stage, it has to not recognize self antigens.

04:39 And that's something called negative selection, because if it does attack a self antigen, you don't want that circulating either.

04:46 So that will be eaten up by macrophages.

04:50 Now, the reason we haven't really talked about the thymus yet is because we're mostly talking about postnatal and largely adult anatomy, and the thymus is really only prominent in the fetal and neonatal period.

05:04 But all the maturation for the most part is kind of done in the early stages of life and so that by the time you reach puberty, even though there is still thymic tissue in the mediastinum, it's really what we say involuted into mostly fat.

05:22 And so in a typical adult mediastinum, it's really hard to even see the thymus.

05:27 It just looks like regular fat that's blending in with other fat in the area.

05:32 Now let's take a look at a different type of circulation than we seen before.

05:36 We've talked about pulmonary circulation between the heart and the lungs in systemic circulation going out to the rest of the body.

05:44 But there's also a form of circulation carried out by lymphatic vessels instead of blood vessels.

05:51 And these lymphatic vessels are spread all throughout the body, and scattered throughout the course of these lymphatic vessels or little lymph nodes.

06:03 Now, in micro anatomic sense, here's the end or in some ways beginning of a lymphatic vessel out in tissue.

06:13 And so the tissue is generally composed of cells in space between the cells called the extracellular space.

06:22 And these very small lymphatics, at this point, they're just little capillaries are just out in the tissue waiting to sample the fluids in the tissue.

06:34 And they're anchored to the surrounding cells.

06:37 So that whenever there's, for example, inflammation of some sort in that extracellular space, that fluid will enter these lymphatic capillaries.

06:49 And now that they're in the lymphatic capillaries, they're going to use these one way valves to make sure that lymphatic fluid flows only in one direction, and that one direction is ultimately toward the venous system.

07:04 But depending on where it is, it's gonna have a long way to go before it gets there.

07:10 Now the majority of lymphatic drainage is going to be off to the left side of the body.

07:17 If we look at the internal jugular veins, those are going to be the major veins draining the neck.

07:23 Then we have the subclavian veins which are the major venous drainage of the upper limbs.

07:30 And where the internal jugular and subclavian veins meet, we have the brachiocephalic veins.

07:37 And this union of the jugular veins and subclavian veins is where we see lymphatic circulation entering the venous system.

07:47 So on the right, we have the right lymphatic duct entering here.

07:52 Again, where the jugular meets the subclavian.

07:55 And then on the left, we have the much larger thoracic duct, same idea it's right about where the jugular and subclavian veins join.

08:06 Now in terms of the anatomy of the drainage, this right lymphatic duct is really only draining the right chest, upper limb and right half of the head and neck whereas the rest of the body is being drained by this larger thoracic duct.

08:25 And if we were to look in a cross section here, where we would see the esophagus and the azygous vein, a big vein that's basically in the middle of the chest, we see that the thoracic duct sits between it.

08:41 So sometimes we say it's the duct between two gooses, between the esophagus and the azygous vein.

08:48 And so that's how you can remember where it's located in the thoracic cavity.