lect 25: Immune and Lymphatic System II Flashcards
what type of lymphatics are present in the capsule of the thymus
efferent are present, afferent are absent
what does the trabeculae (septa) do
divides the thymus into incomplete lobules (delicate CT)
what is the cortex of lobules of the thymus stained with
basic dyes such as H&E
what cells are contained in the cortex of the lobules of the thymus
epithelial reticular cells & T cells in various differentiation
what secretes thymosin
epithelial reticular cells
what is the medulla of the lobules of the thymus specialized to do
allow entry channel into blood stream of mature lymphocytes
what are hassall’c corpuscles
whorls of highly keratinized medullary epithelial cells
produce cytokine thymic stromal lymphopoietin
what does lymphopoietin do
stimulates thymic dendritic cells needed for the maturation of single positive T cells
what are double negative T cells
lack CD4 and CD8
enter cortex from blood vessels
proliferate in subscapular area
what are double positive T cells
move to outer cortex
confronted with epithelial cells with cell surface MHC I 7 II for clonal selection
have CD4 and CD8
where are single positive T cells and what do they express
TCR and either CD4 or CD8 (not both)
where is clonal deletion complete for T cell differentiation
medulla
what expresses keratin 18
cortical thymic epithelial cells
what expresses keratin 5
medullary thymic epithelial cells
what do thymic cortical epithelial cells participate in
clonal selection of immunocompetent T cells
what do thymic medullary epithelial cells participate in
clonal deletion of autoreactived T cells
what does AIRE do
promotes the expression of a portfolio of tissue-specific cell proteins by thymic medullary epithelial cells which normally do not express these proteins (permit identification and disposal of auto reactive T cells)
what does Foxn1 do
essential for differentiation of thymic epithelial cells
where is the blood-thymus barrier located
thymic cortex
what does the blood-thymus barrier prevent
prevents antigens in the blood from reaching developing T cells in thymic cortex
why is the blood-thymus barrier leaky during fetal life
to allow for development of immunologic tolerance to self-antigen
what are the blood filtering functions of the spleen
only lymphatic organ specialized to filter blood stores and removes worn-out RBC recycles iron converts hemoglobin to bilirubin blood formation in the fetus
what are the immunologic functions of the spleen
screens foreign material in the blood
produces lymphocytes and plasma cells
removal leads to overwhelming bacterial infections in infants, children, and young adults
what is the site of clonal expansion of antigen-stimulated lymphocytes
white pulp
