The Lymphatic System and Immunity

Functions Draining excess interstitial fluid Transporting dietary lipids

Lymphatic vessels: In spaces between cells Closed at one end, converge to form larger vessels (like veins) to trunks to right and left duct to venous blood Contain valves to ensure one way movement Flow through lymph nodes (masses of B and T cells) Lymphatic capillaries: Anchored by elastic filaments Open and close with pressure differences

Thymus: Located between sternum and aorta Two lobes divided into lobules Cortex (outer layer) of immature cells -T cells: antigenic activity: -dendritic cells: assist maturation -epithelial cells: “educate” pre-T cells by positive selection -macrophages: clear debris and dead cells Medulla (inner layer) of mature T cells, epithelial cells, dendritic cells, and macrophages

Lymph nodes: Lymph flows in through afferent vessels and out through efferent vessels Made up of nodules -Primary nodules: B cells -Secondary nodules: plasma cell and memory B cell formation

Spleen: Located between stomach and diaphragm Contains white and red pulp -White pulp: lymphocytes and macrophages around central arteries -Red pulp: red blood cells, macrophages, lymphocytes, plasma cells, and granulocytes Removes worn out or defective RBCs Stores platelet Produces blood cells in fetus

MALT Lymphatic nodules: no capsule Throughout mucus membranes (MALT= mucosa-associated lymphatic tissue) Tonsils MALT

Nonspecific Resistance/ Innate Defenses: born with and offer immediate protection First line of defense- skin and mucus membranes Physical and chemical barrier

Nonspecific Immunity Barriers

Phagocyte NK

Helper T Cell Cytotoxin T Cell

Active immunity

Passive immunity