BIOL 1051H Chapter Notes - Chapter 21: Lymph Node, Subclavian Vein, T Helper Cell
The Lymphatic System
The lymphatic system involves a series of lymphatic vessels connecting lymph nodes
together in a chain that eventually empties into the thoracic duct which then empties into the
subclavian veins. The lymphatic system has three main roles. First it picks up fluid that has been
lost by the capillaries of the blood circulatory system. Second, it helps to transport lipids from the
digestive tract to the blood stream. Third, it is a major transport system of immune system cells,
especially lymphocytes. The vessels of the lymphatic system are different from the blood
vasculature in that the flow of lymph begins in the blind ends of lymphatic ducts located in
capillary beds. Flow then moves through a chain of lymph nodes carrying debris including
pathogens, and cells to the nearest lymph node for processing.
The lymph nodes and other secondary lymphatic tissues such as the spleen, pyers
patches, and tonsils serve meeting site for lymphocytes where they can sample the material
picked up in the tissues as start an immune response if needed. The lymph will flow from one
node to the next allowing cells in each successive node to sample dissolved materials. Most of
the lymph eventually makes its way to the thoracic duct with the exception of the upper right
quadrant of the body which drains into the right lymphatic duct. The lymphatic ducts then empty
into the subclavian veins. In this way fluid will be returned to the blood stream and the immune
system is able to survey immunologically important events taking place in the tissues
The immune system is tied to the lymphatic system in that the lymphatic system served
to collect material from the tissues and bring it to the lymph nodes so that lymphocytes can
survey the material. Primary lymphoid tissues are those where lymphocytes are produced and
develop. Bone marrow is the site of lymphocyte production and also serves as the site of
development for B – lymphocytes (B = bone marrow). The thymus is the site of development for
T – lymphocytes (T = thymus). Therefore, both bone marrow and thymus are primary lymphoid
tissue.
The secondary lymphoid tissue are those tissues that serve as meeting places for the
lymphocytes such that lymphocytes can sample antigens (materials that are capable of evoking
an immune response) such as pathogens or debris. It is in the secondary lymphoid tissues that
lymphocytes become activated such that they either produce antibody in the case of B-cells,
become cytotoxic T-cells (those that kill infected cells) or become T- helper cells (cells that help
B cells and macrophages work better).
Other cells of the immune system are worth mentioning here. Macrophages are the
same cell as monocytes in the blood but are located in the tissues. They are important antigen
presenting cells in that they phagocytize foreign material and present it to T cells. Dendritic cells
are a specific class of macrophages that are found in the epidermis, mucous membrane, and
lymphatic organs. They reside in these tissues waiting for foreign material to appear. When it
does, they pick it up and take it to the nearest lymph node to present it to lymphocytes. Reticular
