Lymphoreticular system: spleen & thymus

spleen

thymus

functions

participation in immuno surveillance: T/B cells

source of Extramedullary (outside the bone marrow) hematopoiesis: normal in neonates, abnormal in adults

filtration of peripheral blood: removes particulates and old/damaged erythrocytes

storage pool: reservoir for RBCs and platelets

morphology

enclosed in capsule

two compartments

white pulp: basophilic (from nuclei in lymphocytes), T and B cells, periarteriolar lymphoid sheaths (PALS)

red pulp: screen RBCs, sinusoids (labyrinth of thin-walled vessels creating functional and physical filter through which blood slowly seeps)

site of T-cell maturation

pyramidal, bilobed organ divided into lobules

cells

thymic epithelial cells (have a whorled growth pattern with keratinization)

immature T-lymphocytes (thymocytes)

two compartments

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cortex: immature T-cells

it regresses and atrophies in adults