lymphatic system

• the lymphatic system function :

  1. collects some of the fluid that escapes from capillaries and return to circulatory system
  2. protects against disease 
• Blood enters capillaries at relatively high pressure, causing some blood plasma leaks out of capillaries into tissue. the tissue will swell if the fluid is not removed
• lymph is the fluid that circulates through the lymphatic vessels before returning to the blood
• Fluid leaks out at the arterial end, some of it is returned at the venous end. The excess fluid is returned by the lymphatic system
• lymph does not circulate, it is a one-way system carrying fluid away from the tissue
• lymph capillaries join to make lymph vessels
• lymph vessels originate as blind-ended tubes in the spaces between cells of most tissue
• lymph capillaries are slightly larger than blood capillaries
• lymph capillaries are more permeable than most blood capillaries, allowing proteins and disease-causing organisms in the intercellular fluid to easily pass through the walls into the lymph
• lymph vessels join to form two lymphatic ducts (thoracic and lymphatic)that empties the lymph into large veins in the upper chest (sub-clavian)
• lymph is moved through the vessels by smooth and skeletal muscle, and valves
• the layer of smooth muscle in the vessel contracts to push the lymph along the vessel
• skeletal muscle surrounding the vessel contract to provide additional force
• because there is no central pump, there is no force driving the direction of flow. larger lymph vessels have valves that close when the pressure drops to prevent the backflow of lymph
• lymph nodes are bean-shaped, between 1 to 25 mm in length and occur at intervals along lymphatic vessels
• lymph nodes are most numerous in the neck, armpits, groin and alimentary canal
• lymph nodes are surrounded by a capsule of connective tissue which extends into the node, forming a framework
• within the framework are masses of lymphoid tissue, containing lymphocytes, macrophages and plasma cells
• the spaces between cells of lymphoid tissue are criss-crossed by a network of fibres
• the lymph enters through vessels on convex side of node and filter through spaces. it passes out through vessels on opposite side.

  Lymph passes through several nodes before enter circulatory system
• Lymph contains cell debris, foreign particle, micro-organisms that have penetrated body’s external defence, they may cause disease and need to be destroyed
• larger particles like bacteria are trapped in the meshwork of fibres and destroyed by phagocytic cells called macrophages
• macrophages ingest particles through phagocytosis. projections surrounds the particles and take them into the cell where they are destroyed by enzymes. most bacteria are killed within 10-30 mins this way
• the formation of lymphocytes increase when infection occurs, causing lymph nodes to become swollen and sore. an infected finger can cause swelling and tenderness in the armpits