Lymph Nodes – Secondary Lymphoid Organs (Nursing)

00:01 So starting with the lymph nodes, this is going to be our principal secondary lymphoid organ in the body.

00:09 We have hundreds of lymph nodes found all throughout our body.

00:14 Most of these are going to be embedded deep inside of our connective tissue and clusters along the lymphatic vessels, but some of them are near or closer to the surface of the body, such as in the inguinal area, in the groin area, and the axillary area under the arms, and also in the cervical region where the collecting vessels are going to converge into trunks.

00:40 So what are our functions of these lymph nodes? First, the main function is to act as a filter of the lymph.

00:48 So we're going to be cleansing the lymph.

00:52 Also, macrophages are there to remove and destroy microorganisms and debris that enters in to the lymph.

01:02 And finally, we're going to be preventing unwanted substances from being delivered to the blood.

01:11 On the opposite side, we're also going to be activating the immune system.

01:16 So the lymph nodes are a place where lymphocytes become activated and then from there are able to mount an attack against antigens that have come into the body.

01:29 So let's look at the structure of the lymph node.

01:32 While the lymph nodes vary in shape and size, most of them have a characteristic bean-shaped.

01:38 They look very similar to the kidneys but much, much smaller.

01:44 They are only about 2.5 centimeters or about an inch in size.

01:50 They are surrounded by an external fibrous capsule.

01:54 So again, these are the first of the encapsulated lymphoid organs.

02:01 The capsule fibers also extend inward, and form structures known as trabeulae.

02:08 that divide the nose into separate compartments.

02:12 Histologically, there are two distinct regions found in our lymph nodes.

02:17 We have the outer cortex and the inner medulla.

02:24 The cortex area also referred to as the outer cortex area is the superficial area that contains those lymphoid nodules or follicles with germinal centers that are heavy with dividing B cells.

02:40 Deeper into the cortex, we have the T cells that are in transit.

02:47 These T cells will then circulate continuously among the blood, the lymph nodes, and the lymph kind of doing a little bit of our surveillance.

02:58 There are abundant numbers of dendritic cells that are closely associated with both the T and the B cells found in the cortex area.

03:09 These are going to play a role and activating both lymphocytes.

03:13 So, for the B cells and the outer cortex, these dendritic cells are going to present antigen causing the B cells to develop into antibody producing plasma cells or into memory cells.

03:29 For the T cells found in the inner cortex, these dendritic cells are going to present antigen causing these T cells to proliferate.

03:38 And then these new T cells will go and migrate to other parts of the body where this antigenic activity is taking place so it can fight these antigens.

03:50 The enter portion of the lymph node is the medulla.

03:54 This is gonna include medullary cords, which extend inward from the cortex and contain macrophages as well as antibody-producing plasma cells.

04:07 Also in this area, we have the lymph sinuses, which are found throughout the node.

04:14 These sinuses are going to consist of large lymphatic capillaries that are spanned by crisscrossing reticular fibers.

04:24 Macrophages that reside on these fibers are checking for and phagocytizing any foreign matter that comes in contact with them.

04:35 So, how does the lymph actually circulate through these lymph nodes? The lymph is going to enter on the convex side of the node via vessels known as the afferent lymphatic vessels.

04:51 From there, the lymph is going to travel through these large subcapsular sinuses.

04:57 And then into smaller sinuses that are found throughout the cortex as well as the medulla.

05:04 From there, the lymph is going to enter into the medullary sinuses.

05:10 After that, the lymph is going to exit at the concave side at the hilum, which is going to contain the efferent or afferent lymphatic vessels.

05:24 Because there are fewer efferent vessels then there are afferent vessels, there's going to be a bottleneck or a stagnation of the flow of the lymph through the lymph node.

05:37 This is going to allow the lymphocytes and the macrophages in the lymph node to actually be able to have time to function as the lymph is kind of just sitting there waiting to exit.

05:50 The lymph as it travels through the body will travel through several different lymph nodes.

05:56 So you can be sure that the lymph is being adequately cleaned or filtered as it travels through the body.