SFP: histology of the spleen and GALT Flashcards
What makes the spleen vulnerable to rupture?
Its capsule is very thin.
What are the main structural components of the spleen?
Stroma, white pulp, red pulp.
Describe the stroma of the spleen.
Capsule of dense connective tissue and elastic fibers. There are trabeculae and reticular fibers.
Describe white pulp.
Central arterioles from trabecular artery that are surrounded by a sheath of lymphoid tissue called periarterial lymphatic sheath. There are also splenic nodules.
Describe periarterial lymphatic sheath.
Bunch of lymphoid cells, reticular cells, and fibers surrounding central arterioles.
What cell types are found in periarterial lymphatic sheaths?
T cells (primary cell!!), macrophages, antigen presenting cells.
What is found in splenic nodules?
B cells, reticular cells and fibers, follicular-dendritic cells, germinal centers for B cell proliferation.
Describe red pulp.
Splenic cords with sinusoids in between.
What is found in splenic cords?
A meshwork of reticular collagen, T and B cells, macrophages, RBCs.
Describe the composition of sinusoids.
Made of stave cells that are elongated endothelial cells with discontinuous basal lamina. They have nuclei that bulge into their lumen, are sparsely wrapped in reticular fibers.
What is the orientation of sinusoids?
Oriented in the direction of blood flow.
What is the marginal zone?
Areas where red and white pulp meet.
What cells are found in the marginal zone?
B and T cells, macrophages, APCs.
What are major functions of the spleen?
Removal of aged/damaged erythrocytes, filtering the blood, antigen-independent immune response, hematopoiesis (early in embryonic life).
How does the spleen deal with older erythrocytes?
Macrophages in splenic cords remove them by phagocytosis. Healthy RBCs exit the spleen via sinusoids.
Describe open circulation.
Central arterioles branch into penicillar arterioles in red pulp, then to sheath capillaries. The sheath capillaries dump right into the splenic cords in the tissue. Blood reenters circulation by passing through sinusoids.
Describe closed circulation.
Capillaries from penicillar arterioles drain directly into sinusoids, meaning blood remains vascular. This isn’t really found in humans.
What carries blood from the sinusoids?
Red pulp veins that converge to form trabecular veins.
Where is GALT primarily found?
In the mucosa, specifically the lamina propria.
What are the primary cell types of GALT?
T and B lymphocytes, APCs, plasma cells.
What are forms of GALT in the GI tract?
Diffuse (spread throughout) or solitary nodules of tissue.
What is different about solitary nodules of GALT?
They have a modified epithelium containing M cells.
What are M cells?
Cells in solitary nodules of GALT that take up antigen/pathogens to help transport them to initiate an immune response.
What are Peyer’s patches?
Aggregates of lymphoid nodules in the ileum of the small intestine. The difference is they’re not encapsulated!
What structure contains a lot of unencapsulated lymphoid nodules in a ring?
The appendix.
