Overview of Lymphoid Organs - Video Tutorials & Practice Problems

Primary & Secondary Lymphoid Organs

In this video, we're going to briefly overview the lymphoid organs as we introduce primary and secondary lymphoid organs. However, as we move forward in our course, we're going to talk about all of these lymphoid organs in more detail in their own separate videos. And so in this video, we're really just doing an overview. Now, lymphoid organs as its name implies, are going to be organs with significant amounts of lymphoid cells and lymphoid tissues. And although they may have other specialized functions, primarily, they are going to support immune functions. Now, lymphoid organs can actually be grouped into two functional categories that we have numbered down below in the text, one and two. And these are going to be the primary lymphoid organs and the secondary lymphoid organs. Now, these primary and secondary lymphoid organs are also sometimes referred to as primary and secondary lymphoid structures. Now, primary lymphoid organs are going to be where T and B cells or T and B lymphocytes mature and become immunocompetence, which means becoming capable of carrying out an effective and appropriate immune response toward a specific pathogen or antigen. However, although T and B cells mature and become capable of carrying out an immune response. It's important to note that they do not actually carry out an immune response in the primary lymphoid organs. And so the primary lymphoid organs do not directly participate in immediate immune responses. That's where the secondary lymphoid organs come into play. And so the primary lymphoid organs include the thymus, which is where T cells develop and the red bone marrow, which is where B cells develop. And so you can think that the T in thymus is for the T and T cell development, which is why we have the T bolded. And you can think that the B in red bone marrow is for the B and B cell development, which again is why we have the B bolded. However, it's important to note that both B cells and T cells are initially produced in the red bone marrow. However, after being initially produced, the B cells remain in the red bone marrow to fully mature and become immunocompetence. Whereas the premature T cells will migrate away from the red bone marrow and toward the thymus where they mature and become immunocompetence. So, again, that's important to keep in mind. Now, after the T and B cells mature and become immunocompetence, they will migrate from the thymus and the red bone marrow to the secondary lymphoid organs. And unlike the primary lymphoid organs, the secondary lymphoid organs do directly participate in immediate immune responses. So this is going to be where the T and B cells or T and B lymphocytes first encounter their antigens and become activated, which means that they are going to actively carry out the immune response. Either right then and there in the secondary lymphoid organ, when they first encountered the antigen, or they may migrate to the site of infection using the bloodstream where they carry out the immune response there. Now, the secondary lymphoid organs are going to include lymph nodes which are scattered all throughout our body and we'll get to talk a lot more about them later in our course. And it also includes the spleen and collections of malt or mucosal associated lymphoid tissues including tonsils which are found in our head and the pyres patches and the appendix which are found in the digestive system. And so notice down below in the image, we've got the secondary lymphoid organs labeled over here on the right hand side of the image. And we've got the primary lymphoid organs over here on the left side. And so again, the primary lymphoid organs include the thymus, which is located right here in the diagram. And this is where the T cells develop. And it also includes the red bone marrow, which is going to be found in the ends of long bones such as the humerus here. And that is going to be where the B cells develop. And so this year concludes our brief overview of the lymphoid organs. But again, as we move forward in our course, we're going to talk about all of these lymphoid organs in more detail in their own separate videos. But for now that concludes this video and we'll get some practice applying these concepts moving forward. So I'll see you all in our next video.

Overview of Lymphoid Organs Example 1

So here we have an example problem that asks in which of the following organs do lymphocytes become immunocompetence? And we've got these four potential answer options down below. Now, recall from our last lesson video, that the term immunocompetence means being capable of carrying out an effective and appropriate immune response towards a pathogen or foreign substance. And recall that there are two main types of lymphocytes and those are the B lymphocytes or the B cells and the T lymphocytes or the T cells. And recall that although the B cells and T cells are both initially produced in the red bone marrow, only the B cells remain in the red bone marrow to become fully immunocompetence. However, the T cells will migrate away from the red bone marrow in a premature state to the thymus where they can become fully immunocompetence. And so the two organs where lymphocytes become immunocompetence are the thymus and the red bone marrow. And notice that answer, option D says thymus and red bone marrow. And so option D is the correct answer to this example problem and these other options are not going to be correct. So that concludes this example problem and I'll see you all in our next video.

Which of the following statements about the development of lymphocytes is correct?

• A. T cells are produced in the thymus & B cells are produced in red bone marrow.
• B. T & B cells are both produced in red bone marrow, & they both mature in the thymus.
• C. T & B cells are both produced in red bone marrow, but only T cells mature in the thymus.
• D. T & B cells are both produced in the thymus & also mature in red bone marrow.

A patient comes to you after experiencing multiple infections in a short period of time. Analysis reveals that she has a very low white blood cell count. Which lymphoid organ is likely not functioning correctly?

• A. Lymphatic capillaries.
• B. Tonsils.
• C. Red Bone Marrow.
• D. Thoracic Duct.