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BIOL 301
Vivian Dayeh

CHAPTER 21 - THE LYMPHATIC SYSTEM THE LYMPHATIC SYSTEM − Contains the following components: o Vessels o Organs (lymphatic tissue plus cells) o Fluid − Function of the lymphatic is: o Transport fluid  lymph  Return tissue fluid and proteins to the blood  A one-way system  fluid only flows toward the heart o Immune response  protection from pathogens Lymphatic vessels − Collect excess tissue fluid from loose CT − Carry fluid to great veins in the neck − Once tissue fluid is within lymphatic vessels it is termed lymph o Any blockage in the lymphatic vessels causes affected body region to swell with excess lymph, a condition known as edema. − Includes: o Lymphatic capillaries  Smallest lymph vessels  first to receive lymph  Walls consist of single layer of endothelial cells.  High permeability allows entrance of: • Tissue fluid and protein molecules • Bacteria, viruses, and cancer cells  Specialized lymphatic capillaries  lacteals • Located in the villi of the small intestines o Receive digested fats o Fatty lymph  chyle  Lymphatic capillaries are absent from bone and teeth, from bone marrow, and the entire CNS. o Lymphatic collecting vessels  Collect from lymph capillaries • Lymph nodes are scattered along collection vessels  Collecting vessels accompany blood vessels • Superficial vessels travel with superficial veins • Deep vessels of the trunk and digestive viscera travel with deep arteries • Composed of the same 3 tunicas as blood vessels, but their walls are thinner • Contain more valves than veins  one way flow  Lymph propelled by: • Skeletal muscles bulging, nearby arteries pulsing • Tunica media of the lymph vessels  Lymph flow is unaided by heartbeat o Lymph nodes  Cleanse the lymph of pathogens; bean-shaped  Superficial lymph nodes are located in: • Cervical nodes  along the jugular veins and carotid arteries, receive lymph from head and neck • Axillary nodes  in armpit; filter lymph from upper limbs • Inguinal (groin) nodes  in superior thigh; filter lymph from lower limbs  Deep nodes are: • Tracheobronchial nodes  in mediastinum; receive lymph from thoracic viscera. • Aortic nodes  along abdominal aorta; filter lymph from posterior abdominal wall • Iliac nodes  along iliac arteries; filter lymph from pelvic organs and lower limbs.  Microscopic anatomy of a lymph node: • Fibrous capsule  surrounds lymph nodes • Trabeculae  dense CT strands formed by fibrous capsule • Lymph vessels  afferent (enter) and efferent (exit) lymphatic vessels • Lymph sinuses  between the afferent and efferent vessels: • Subscapular, cortical, and medullary sinuses. o Lymphatic trunks  Lymphatic collecting vessels converge into lymphatic trunks (largest collecting vessels)  There are 5 major lymphatic trunks (from inferior to superior) • Lumbar trunk
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