NOTES: The Lymphatic / Immune System (Ch 12, part 1) The lymphatic system is closely associated with the cardiovascular system. Functions of the Lymphatic System: ● transports excess fluid to the bloodstream ● absorbs fats ● helps defend the body against disease- causing agents LYMPHATIC PATHWAYS Lymphatic capillaries ● microscopic, closed-end tubes that extend into intercellular spaces ● receive LYMPH through their thin walls (LYMPH = the fluid of the lymphatic system … more later!) ● lymphatic capillary networks parallel blood capillary networks Lymphatic vessels: ● have walls similar to those of veins, but thinner, and have valves to prevent backflow of lymph ● become larger and lead to LYMPH NODES and then merge into LYMPHATIC TRUNKS Lymphatic Trunks and Collecting Ducts: ● lymphatic trunks lead to two collecting ducts: -THORACIC DUCT larger and longer duct ; receives lymph from the lower limbs, abdominal regions, left upper limb, left side of thorax, head, and neck -RIGHT LYMPHATIC DUCT receives lymph from the R side of the head & neck, R upper limb, R thorax ● collecting ducts join the SUBCLAVIAN VEINS Tissue Fluid & Lymph: ● LYMPH is essentially tissue fluid that has entered a lymphatic capillary ● tissue fluid originates from blood plasma and is composed of: -water -dissolved substances that leave blood capillaries (small molecules, nutrients, gases, hormones) **NOT present are larger plasma proteins (too large to pass through capillary walls) Functions of lymph: 1) returns to the bloodstream small proteins that leaked out of blood capillaries 2) transports foreign particles , such as bacteria or viruses, to lymph nodes Lymph Movement ● lymph, like venous blood, is under low pressure and may not flow readily ● movement of lymph is affected by skeletal muscle contraction and pressure changes associated with breathing **if lymph movement is impaired, it may accumulate within the intercellular spaces and produce EDEMA, or swelling (example : after surgery, the lymphatic vessels and lymph nodes around the wound may be damaged, causing fluid to accumulate around the surgery site and lead to swelling) Lymph Nodes: Structure of a Lymph Node: ● lymph nodes are subdivided into nodules ● nodules contain masses of lymphocytes and macrophages Locations of Lymph Nodes: ● lymph nodes aggregate in groups or chains along the paths of larger lymphatic vessels Functions of Lymph Nodes: ● filter potentially harmful foreign particles from lymph ● are centers for the production of lymphocytes (attack invading viruses, bacteria, parasites, etc.) ● contain phagocytic cells (engulf and destroy foreign substances, damaged cells, cellular debris) THYMUS AND SPLEEN Thymus: ● located anterior to aorta and posterior to upper part of sternum ● shrinks slowly after puberty ● contains large numbers of LYMPHOCYTES which mature into T CELLS (T lymphocytes) – important in providing immunity (more on these later…) Spleen: ● largest lymphatic organ ● located in upper left portion of abdominal cavity (just inf. to diaphragm and lat./post. to stomach) ● resembles a large lymph node (divided into lobules) Spleen: ● spaces within splenic lobules are filled with blood ● contains many macrophages, which destroy/remove foreign particles and damaged RBCs from the blood **the spleen filters blood as the lymph nodes filter lymph !**.