Flashcards in Immune and lymphatic system II Deck (33):
What is present in the capsule of the thymus?
blood vessels, efferent lymphatics and trabeculae.
What type of lymphatics are not present in the capsule of the thymus?
afferent lymphatics. Therefore, lymph does not circulate through the thymus.
What are the trabeculae of the thymus?
connective tissue what divides the thymus into incomplete lobules.
What are the components of the lobules?
an outer darker cortex and a light medulla.
What is in the lobules of the cortex?
T cells, blood vessels, and epiithelial reticular cells that release thymosin.
What does thymosin do?
Directs the differentiation of T cells.
What do the blood vessels in the thymus do?
Allow the thymus to maintain lymphopoiesis while segretated from antigens.
What is the function of the medulla?
allows the entry of mature lymphocytes into the bloodstream.
What are Hassall's corpuscles?
highly keratined medullary epithelial cells that produce cytokine thymic stromal lympopoietin.
What does thymic stromal lymphopoietin do?
stimulates thymic dendritic cells needed for the maturation of single positive T cells.
When is the thymus most developed?
What are double negative T cells?
cells that lack surface molecules typical of mature T cells (TCR, CD4 or CD8). The enter the cortex from blood vessels and proliferate in subscapular areas.
What are double positive T cells?
Cell that express both CD4 and CD8 coreceptors and TCR receptors. They are confronted with epithelial cells with clel surface MCH classes I and II for clonal selection.
what are single positive T cells?
cells that express TCR recepttors and either CD4 or CD8 receptors.
Where does clonal deletion occur?
What is the function of the blood-thymus barrier?
to prevent antigens in the blood from reaching developing T cells in the thymic cortex. They are leaky during fetal life to allow for development of immunologic tolerance to self-antigen.
What are some characteristics of the spleen?
it has no lymph sinuses or afferent lymph vessels and is covered by peritoneum except at the hilus. It has blood vessels that enter and leave the hilus, and is divided into red pulp and white pulp.
What is the function of the slpeen?
to store and remove worn-out RBCs. It also recycles iron and is important for blood formation in the fetus. It screens foreign material in the blood and produces lymphocytes and plasma cells.
What happens if the spleen is removed?
bacterial infections in infants, children and young adults occurs.
What is the white pulp?
It contains elongated branched strands associated with artieries and well as zones of diffuse lymphoid tissue and germinal centers. It contains B cells and T cells and reticular fibers.
What is the marginal zone?
A zone that forms a sinusoidal interface between red pulp and white pulp. it has an abundance of antigen presenting cells and is where lymphocytes first encounter antigens.
Activated T-helper cells activate B cells in what region?
The marginal zone.
Red pulp surrounds what other pulp?
The white pulp. Red pulp makes up about 80% of the spleen.
What does red pulp do?
filters blood and contains large numbers of RBCs and other blood elements.
What is in the red pulp parenchyma?
various blood cells, plasma cells, and antigen presenting cells.
Where do terminal capillaries of the red pulp open directly to?
substance of cords (open circulation).
What destroys worn-out or defective red blood cells in the red pulp?
What are the venus sinusoids of the red pulp?
endothelial-lined sinusoids with a discontinuous basement membrane that are storage sites for healthy red blood cells.
What artery enters the hilus?
the splenic artery
After capilaries supply the white pulp, what happens to the central arteries?
they lose their white pulp investment and enter red pulp to form a penicillus.
What is the penicillus?
A pump arteriorle, sheated arteriole and terminal capillary.
What does the terminal capillary of the penicillus drain into?
intercellular spaces (open system) or venous sinuses lined with reticuloendothelial cells (closed system)