Chapter 20: Lymphatic system

• Returns fluids that leaked from blood vessels back to blood
• 3 Parts - lymphatic vessels, lymph, lymph nodes

• Structural basis of immune system
• House phagocytic cells and lymphocytes
• Structures - spleen, thymus, tonsils, other lymphoid tissues

• Return interstitial fluid and leaked plasma proteins back to blood
• One way-system; lymph flows toward heart
• ~ 3L / day
• Lymphatics include - lymphatic capillaries, collecting lymphatic vessels, lymphatic trunks and ducts

• Fluid in the lymphatics
• [leaks out of capillaries]

Very permeable (taking up proteins, cell debris, pathogens, and cancer cells)

• specialized lymph capillaries present in intestinal mucosa
• Absorb digested fat and deliver fatty lymph to the blood

• Similar to veins, except - they have thinner walls with more internal valves, anastomose more frequently
• Collecting vessels in skin travel with superficial veins
• Deep vessels travel with arteries
• Lymphatic vessels drain into lymphatic trunks

• Lymphatic delivered into one of two large ducts (right lymphatic duct, thoracic duct)
• Each empties lymph into venous circulation at junction of internal jugular and subclavian veins on its own side of body

• Drains right upper arm and right side of head and thorax
• Drains rest of body

• Milking action of skeletal muscle
• Pressure changes in thorax during breathing
• Valves prevent backflow
• Pulsations of nearby arteries
• Contractions of smooth muscle in walls of lymphatics

Lymphocytes - main warriors of immune system - mature into one of two main varieties (B cells - humoral immunity, T cells - cell-mediated immunity)

• Manage immune response
• Attack and destroy infected cells
• [attack cells]

• Product plasma cells, which secrete antibodies
• [defense cells]

mark antigens for destruction

• Phagocytize foreign substances
• Help activate T cells
• [antigen-preventing cells]

capture antigens and deliver them to lymph nodes

• 1. Filter lymph
• 2. Immune system activation - lymphocyte activated and mount attack against antigen

• Medullary cords extend inward from  cortex and contain B cells, T cells, and plasma cells
• Nodes are embedded in the connective tissue!

contain macrophages

• Site of lymphocyte proliferation and immune surveillance and response
• Cleanses blood of aged cells and platelets, macrophages remove debris
• Stores products of RBC destruction for reuse
• Stores platelets and monocytes until needed
• [storage unit]

• Important functions early in life
• Increases in size and most active during childhood

• Lymphoid tissues in mucous membranes hroughout body
• Protects from pathogens trying to enter body
• Largest collections of MALT in tonsils, Peyer's patches, appendix
• Also in mucosa of respiratory and genitourinary organs; rest of digestive tracts

• Gather and remove pathogens from food and air
• Form ring of lymphatic tissue around pharynx
• Palatine tonsils - at posterior end of oral cavity
• Lingual tonsil - grouped at base of tongue
• Pharyngeal tonsil - in posterior wall of nasopharynx (adenoids)
• Tubal tonsils - surrounding openings of auditory tubes into pharynx

• Clusters of lymphoid follicles
• In wall of distal portion of small intestine
• Similar structures are also found in the appendix

• Destroy bacteria, preventing them from breaching intestinal wall
• Generate "Memory lymphocytes"