In this video, we're going to begin our lesson on primary lymphoid organs by focusing on red bone marrow. Now recall from our previous lesson videos that red bone marrow serves as the primary site of hematopoiesis, which recall is blood cell formation. This will include lymphocytopoiesis, which is lymphocyte formation or the formation of both T and B lymphocytes, or T and B cells. So what this means is that both T and B cells are going to originate and initially be produced in the red bone marrow. However, recall that after being initially produced, the B cells will remain in the red bone marrow to fully mature and become immunocompetent, whereas the T cells, on the other hand, will migrate away from the red bone marrow in their immature states to the thymus where they will mature and become immunocompetent.
Notice that this is precisely what we're showing you down below in this image. So on the far left, we've got this long bone, and at the end, you can see the red bone marrow, where, again, both the T and B cells originate and are initially produced. But, after being initially produced, the B cells remain in the red bone marrow to fully mature and become immunocompetent. After becoming fully mature and immunocompetent in the red bone marrow, these mature B cells will migrate from the red bone marrow to the secondary lymphoid organs, such as the lymph nodes, for example.
Below here, we can fill this box in with secondary lymphoid organs. The secondary lymphoid organs are where they are going to encounter their antigen for the first time and ultimately become activated to carry out an immune response. Now, on the other hand, although the T cells are initially produced in the red bone marrow, they do not mature and develop there like the B cells do. Instead, the T cells will migrate away from the red bone marrow in their immature states using the bloodstream to the thymus, and in the thymus, they will mature and become immunocompetent. Then after becoming mature, those T cells are going to migrate from the thymus to the secondary lymphoid organs using the bloodstream, where, again, they will encounter their antigens for the first time and carry out immune responses.
The last thing I'll leave you with is that the hematopoiesis and lymphocytopoiesis processes of the red bone marrow are actually covered in detail in other videos, so be sure to see those videos if you haven't yet seen them. This here concludes our brief lesson on the red bone marrow, one of the primary lymphoid organs, and in our next lesson video, we'll talk more about the thymus, which is the other primary lymphoid organ. So I'll see you all there.