Page 459 - Atlas of Histology with Functional Correlations

Distributed along the paths of lymphatic vessels

Most prominent in inguinal and axillary regions
Major function is lymph filtration and phagocytosis of foreign material from
lymph
Surrounded by connective tissue capsule that sends trabeculae into the
interior of the organ

Exhibit an outer dark-staining cortex and an inner light-staining medulla
Lymphatic nodules, some with germinal centers, are aggregated in the cortex
Lymphatic nodules without germinal centers are primary lymphatic nodules

Lymphatic nodules with antigen stimulation and lighter germinal centers are
secondary nodules
Afferent lymph vessels with valves penetrate the capsule and enter
subcapsular sinus
Major blood vessels present in connective tissue trabeculae

Medullary cords in the medulla contain plasma cells, macrophages, and
lymphocytes
Medullary sinuses are capillary channels that drain lymph from cortical

regions
Efferent lymphatic vessels drain lymph from the medullary sinuses to exit at
the hilus
Produce and store B and T cells
B cells accumulate in lymphatic nodules and when activated form germinal

centers
Deeper region of the cortex is the paracortex, occupied by T cells
T cells concentrate in deep cortical or paracortex regions

Activate B cells to give rise to plasma cells and memory B cells
B and T cells enter lymph nodes through postcapillary high endothelial
venules
High endothelium in postcapillary venules contains adhesive molecules as
homing receptors for lymphocytes

Both B and T cells leave bloodstream through high endothelial venules
High endothelial venules present in numerous other lymphoid organs except
the spleen

CELLS OF THE IMMUNE SYSTEM

Include lymphocytes and different supporting cells

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