Capsule - connective tissue that surrounds the organ; septa from the capsule divide the organ into incomplete lobules

Cortex - contains immature T-lymphocytes (thymocytes), epithelial reticular cells, and macrophages; has a blood-thymus barrier

Medulla - contains mature T-lymphocytes (leave via postcapillary venules at cortical/medullary junction), epithelial reticular cells, and Hassel's corpuscles; NO blood-thymus barrier

The thymus has efferent lymphatics, afferent lymphatics, both, or neither?

a.) Describe the structural basis of the blood thymus barrier.

b.) Why is it important?

a.) Non-fenestrated capillaries composed of endothelial cells with tight junctions; continuous basement membrane of capillary; adjacent associated macrophages

b.) Critical for the process of learning to distinguish self from non-self

a.)What is the function of postcapillary venules in the thymus?

b.) Where are they located?

a.) Mature T-lymphocytes exit the thymus through postcapillary venules

b.) They are located at the cortex/medulla junction

A primary nodule is a cluster of unstimulated lymphocytes

A secondary nodule develops froma primary nodule after antigenic stimulation; contains more cytoplasm and has blast and plasma cells

a.) What is the humoral immune function in secondary lymphoid tissue?

b.) What is the cell-mediated immune function in secondary lymphoid tissue?

a.) Antigen stimulation, B-cell blast transformation and proliferation of lymphocytes, and antibody production and secretion

b.) Antigen stimulation, T-cell blast transformation and proliferation of lymphocytes; exit of cells from secondary organs/contact and destruction of antigen

Unencapsulated lymphoid tissue found in the mucosa and submucosa of the gastrointestinal, respiratory and genitourinary tracts; it protects common sites of microbial invasion when lumens are open to the external environment

Examples include Gut Associated Lymphoid Tissue (GALT), tonsils, Peyer's patches, and appendix

a.) What types of tonsils are lined with stratified squamous epithelium?

b.) What types of tonsils are lined with ciliated pseudostratified columnar epithelium?

a.) Palatine and Lingual tonsils

b.) Pharyngeal tonsils

Outer cortex - contains diffuse lymphatic tissue rich in T-lymphocytes; contains nodular lymphatic tissue with and/or without germinal centers

Inner cortex - rich in diffuse lymphatic tissue; lacks nodular lymphatic tissue

 The cortex contains the intermediate sinus

Medullary cords - branched extensions of dense lymphatic tissue arising in the cortex; contain primarily B lymphocytes, plasma cells, and macrophages

Medullary sinuses - dilated spaces continuous with intermediate sinus that seperate cords; often bridged by reticular fibers and cells; join at the hilum to deliver lymph to the efferent lymphatic vessels

Surrounded by a dense connective tissue capsule; trabeculae arise from the capsule and subdivide the splenic pulp into incomplete compartments; large trabeculae arise from at hilum and carry arterial supply and nerves into spleen, venous drainage and lymphatics out of the spleen

Pulp is divided into white and red pulp

Sinusoids - elongated, discontinuous endothelial cells; discontinuous basal lamina; filtration slits

Splenic (Billroth's) cords - loose connective tissue/reticular fibers; capillaries; red blood cells, macrophages, platelets, plasma cells, and reticular cells

Splenic artery

Trabecular artery

Central artery (PALS)

Penicillar arteriole (PALS is lost; in white pulp)

Sheathed capillaries

Splenic cords (cells migrate through tissue)

Sinusoids

Pulp

Trabecular

Splenic veins