Lymphatic system microanatomy

histologic appearance

small, dark, boring

small cells

dense round nucleus

scant cytoplasm

functions of the lymphatic system

transport of materials via lymphatic vessels

filtration of lymph and blood—phagocytosis of foreign material

production of defensive cells

production of immunoglobulins (antibodies)

primary lymphoid organs

produce and train lymphocytes

marrow, bursa (birds), thymus

secondary lymphoid organs

surveillance of incoming pathogens

lymph nodes, spleen, mucosa associated lymphoid tissue (MALT)

diffuse unencapsulated

GI tract and resp tract (tissue exposed to the outside)

loose collection of leukocytes

-lymphocytes (mostly T cells)

macrophages

plasma cells

diffuse unencapsulated lymphoid tissue

individual cells not forming an aggregate or mass like structure

diffuse unencapsulated

individual cells do not form an aggregate or mass-like structure

subepithelial aggregates of leukocytes (lymphocyte, macrophages, plasma cells)

**tonsils

specialized epithelium has M cells (cannot be seen except electron microscopy)

crypts of tonsils

epithelium invaginates into lymphoid tissue

horses, swine, sheep, goats, humans (carnivores usually lack)

depends for ruminants

african and classical swine fever

hemorrhaging of the tonsils

MALT

mucosal associated lymphoid tissue (MALT)

dense unencapsulated

GLAT (GI)

Peyers patch

dense unencapsulated