Key Terms
RIGHT LYMPHATIC DUCT
Drains only upper right side of body (right head, right thorax, right upper limb) into the right subclavian vein.
THORACIC DUCT
Drains everything else (lower body, left side) into the left subclavian vein. Begins at the cisterna chyli just below th
LACTEALS
Specialized lymphatic capillaries in the small intestine that absorb dietary lipids; they form chyle, a milky lipid-rich
LYMPHEDEMA
When lymphatic vessels are blocked or destroyed, protein- rich fluid accumulates in tissue spaces; can cause serious com
PRIMARY LYMPHOID ORGANS
Where lymphocytes mature and develop
SECONDARY LYMPHOID ORGANS
Where mature lymphocytes mount immune responses
THYMIC INVOLUTION
Thymus begins shrinking at birth at approximately 3% tissue loss per year; slows to 1% per year after age 35-45; linked
Three functional classes
1. Phagocytic cells: ingest and destroy pathogens 2.
B CELLS
Recognize native, unprocessed antigen without MHC molecules. Activated B cells differentiate into plasma cells, which se
T CELLS
Require antigen to be processed and presented on MHC molecules. Do not recognize free-floating antigen.
NK CELLS
Circulating innate immune cells containing cytotoxic granules; recognize virally infected cells and some cancer cells; f
THREE PHASES OF IMMUNE DEFENSE (in order of speed)
1. Barrier defenses: instantaneous; physical prevention 2.
NOTE
Some bacteria (like Mycobacterium tuberculosis) resist lysosomal enzymes and persist inside macrophages.
NK CELL KILLING MECHANISMS (two pathways)
1. Fas ligand pathway: NK cell expresses fas ligand, which binds to fas molecule on infected cell surface, triggering ap
PATTERN RECOGNITION RECEPTORS (PRRs)
Membrane-bound receptors on innate immune cells that recognize characteristic features of pathogens (like bacterial cell