Lymphoid system Flashcards
lymphoid organ types
primary or secondary
primary lymphoid organs
Bone Marrow or Thymus
discrete, covered by epithelium/CT
secondary lymphoid organs
isolated masses of cells
Immunocompetent T cells develop in the
thymus
immunocompetent B cells develop in the
bone marrow
immunonocompetent cell development in primary organ
thymocyte/ B cell precursor> developing cells with receptors against anything > anything BUT SELF
Thymus
involutes with age. Lobulated with septa. “Starry night”, white spaces are macrophages. Surrounded by CT capsule, which septa penetrate inwards from. Basophillic areas are full of lymphocytes while lighter region is medulla (continuous)
epithelioreceptor cells
long extending fibers that connect via desmosomes. The form network supporting lymphocytes, and release hormones that recruit lymphocytes to mature. (Thymus has no Reticular fibers)
Hassalls corpuscles
whorls of epithelioreceptor cells, reside in thymic medulla, diagnostic for thymus. Grow with age, even post puberty.
Secondary lymphocytes are classified as either?
unencapsulated or encapsulated
Unencapsulated secondary lymphoid organs
tonsils, peyers patch, appendix
encapsulated secondary lymphoid organs
Lymph nodes and spleen
Secondary lymphoid all have what?
nodular and diffuse lymphoid tissue
Lymphoid nodules
B cell proliferation. Have germinal center. Also contain macrophages. When a B cell is activated, it will move from nodule to CT, where it becomes plasma cell.
diffuse zones
are between nodules, full of T cells
MALT
mucose associated lymphoid tissue
occurs in lamina or submucosa
Tonsil types
palatine, pharyngeal, lingual: all look the same at high magnification - need to see surface covering to distinguish
palatine tonsil
stratified squamous epithelium of oral cavity (SSNKE). Crypts present increase surface area.
Pharyngeal tonsil
respiratory epithelium covering.
Peyers patch
usually in ileum, mucosa related. M cells present in epithelia, which give broken appearance
M cells
microfold cells, deep basal invaginations. take in antigens via pinocytosis
appendix
unencapsulated secondary lymphoid. Lumen lined by epithelium, nodules and lamina.
functions: immune surveillance, endocrine organ, reserve of gut flora, surgical substitute
lymph node
variable sizes, concentrated on neck, axilla, and groin. filter lymph and expose antigens to immune cells
surrounded by dense CT. Medullary cords and sinuses.
medullary cord
loose CT, highly cellular. Reticular fibers. Lots of plasma cells.
medullary sinuses
venous channels that divide cords, discontinuous endothelium. traversed by reticular fibers
Splenic cord/sinuses
similar to lymph medullary except: blood cells in both; no reticular fibers in sinuses
Lymph flow
afferent> efferent, with efferent often becoming afferent of next node. More afferent than efferent slows down fluid- more time for antigen exposure.
3 mechanisms to insure lymphocytes meet pathogens
1) sinuses lined by discontinuous endothelium
2) reticular fibers transverse all sinuses
3) afferent lymphatics outnumber efferent> bottleneck
High Endothelial Values
lymphocyte entry, lymphocytes stick.
Spleen functions
immune response (b/t), destroy damaged RBC, sequester monocytes, heatopoisis, storage of platelets, recycling iron
Does the spleen have cortex/ medulla?
NOPE. Just random pulp
Red pulp
full of RBC, eosinophilic in H/M
white pulp
full of WBC, basophilic on H/M
Traveculae in spleen
extend into spleen, artery and vein
red pulp cords
loose CT/ reticular fibers. Contains RBC, platelets, macrophages, plasma cells, lymphocytes
Red pulp sinuses
venous channels with discontinuous endothelial cells.
discontinuous basal lamina. NO RETICULAR FIBERS
PALS
pulp areas surrounding central artery
marginal zone
location of first antigen exposure- lots of reticular fibers
spleen has open circulation
filters out old RBCvia stave cells in cord areas.
