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
where are T cells founds in the white pulp
areas surrounding the central artery near the center of the white pulp (forms the PALS)
what are reticular fibers of white pulp associated with
fixed macrophages and support splenic pulp
what does the marginal zone of the spleen do
forms sinusoidal interface between red pulp and white pulp
where do lymphocytes first encounter antigens
marginal zone
where do activated T-helper cells activate B cells
marginal zone
what is the main function of Red Pulp
filter blood
what occurs in billroth cords
contain various blood cells, plasma cells, and antigen-presenting cells
terminal capillaries open directly into substance of cords (open circulation)
macrophages destroy worn out or defective RBC
where do billroth cords come form
red pulp parenchyma
what is the most important aspect of venous sinusoids
storage sites for healthy RBC
what is penicillus composed of
pulp arteriole, sheathed arteriole, and terminal capillary
where does the terminal capillary drain into to
intercellular spaces (open system) or venous sinuses (closed system)
what are venous sinuses lined with
reticuloendothelial cells
where do venous sinuses drain into (course)
venous sinuses–> drain into pulp veins–> unite with trabecular veins–> forming splenic veins–> exits at hilus
what releases immunoglobulins into the blood circulation
plasma cells
what is the main function of the macrophage sheath
remove aged cells and particles from the blood
