Thymus – Primary Lymphoid Organs (Nursing)

00:00 The next lymphoid organ that we're going to discuss is the thymus.

00:04 The thymus is a bilobed lymphoid organ that is found in the inferior neck and extends into the mediastinum and partially overlies the heart.

00:16 This organ is going to function to mature our T cells.

00:21 So recall that T cells are formed in the bone marrow, but they mature in the thymus.

00:29 The thymus is most active and largest during childhood.

00:33 But as you grow, it starts to atrophy or gets smaller and eventually stops growing.

00:40 This growth stops during adolescence.

00:44 Even though it has atrophy and it's much smaller in an adult it is still able to produce immunocompetent cells.

00:52 It just produces them much more slowly than it did when you were a child.

00:59 The thymus is broken into lobules they contain both an outer cortex and an inner medulla.

01:07 The outer cortex contains rapidly dividing lymphocytes, which are the bulk of our thymic cells and also a few scattered macrophages.

01:18 The medulla region of the thymus is going to contain fewer lymphocytes and thymic corpuscles.

01:25 The thymic corpuscles are where the regulatory T cells are going to develop.

01:31 And this is the type of T cell that helps to prevent autoimmunity.

01:35 So while we talked about T cells that are attacking antigen, it's also important that we notice that there are also T cells that are regulatory, that are going to make sure that our T cells are attacking our own body cells.

01:50 This is where they are going to be located.

01:54 The thymus differs from other lymphoid organs in some important ways.

01:59 First of all, there are no lymphoid follicles in the thymus.

02:03 And because there are no lymphoid follicles, there are no B cells.

02:09 It also does not directly fight antigens.

02:13 So basically the thymus is only function is T-lymphocyte maturation.

02:20 Also in the thymus, we have something known as the blood-thymus barrier.

02:26 What this does is it keeps the immature lymphocytes that are being matured there, isolated away from antigens, because again, we're not fighting antigens here, we're just maturing these T lymphocytes.

02:39 So, we don't want any premature activation of T lymphocytes in this area.

02:47 The thymus also contains a stroma, which is made up of epithelial cells instead of the reticular fibers that we've seen in the other lymphoid organs.

02:58 These epithelial cells are going to provide an environment in which the T lymphocytes become immunocompetent.