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Chapter 32: The human lymphatic system Leaving Certificate Biology Higher Level The Lymphatic System • Involves a one-way system of vessels that returns excess tissue fluid to the bloodstream • Tissue fluid is the extremely thin layer of fluid (plasma) that surrounds all cells and comes from diffusion of plasma through capillary walls • Diffusion occurs through the capillary wall due to blood pressure • Lymph vessels, like capillaries, are present throughout all tissues and collect this excess tissue fluid which is then called lymph • After entering the lymph vessel it travels back to the blood through the subclavian veins (3L/d) Lymphatic System Flow of Lymph • Lymph flows along the lymph vessels by rhythmic contraction of the muscular walls of the lymph vessels and by contraction of the skeletal muscles • Lymph vessels (like veins) have valves to prevent backflow of lymph • The lymphatic drainage system is absent from the teeth, bone, bone marrow, and the central nervous tissue Lymph Nodes • Lymph nodes are small bean-shaped structures that have dense masses of lymphocytes and monocytes • They are widely distributed throughout the body along the lymphatic pathways where they filter the lymph before it is returned to the blood • Lymph nodes are not present in the central nervous system • There are three superficial regions on each side of the body where lymph nodes tend to cluster: – Groin – Armpit – Neck The Lymphatic System • There are two general roles of the lymphatic system: – Circulatory role – Defence role The Lymphatic System • Circulatory role: – Returns the proteins lost from capillaries – Returns fluid lost from capillaries – maintains blood pressure and volume – Removes excess tissue fluid – prevents swelling (oedema) – Collection of lipids from the small intestine and transfer to the blood via the subclavian veins The Lymphatic System • Defence role: – Bacteria, viruses, cancer cells, cell debris and toxins are removed from the lymph by lymph nodes – Lymph nodes continually monitor lymph for infections and cancer – Lymphocytes and monocytes multiply in lymph nodes during an infection