Lecture 32: Lymphoid organs Flashcards
primary lymphoid organs
bone marrow, thymus
secondary lymphoid organs
lymph nodes, spleen, MALT
MALT
mucosa associated lymphoid tissue
- Diffuse populations of lymphoid cells in the mucosa
- Lymphoid follicles of the GI, respiratory and genitourinary tracts
- Peyer’s patches of the ileum
- Tonsils
sources from lymphocytes
bone marrow (ULTIMATE)
bone marrow makes
1) T cell precursor that goes to thymus where they mature into helper and cytotoxic
2) Mature B cells
* both end up in secondary lymphoids
what do helper t cells do
activate cytotoxic t cells
what to cytotoxic t cells do
- Kill tumor cells, virus-infected cells, etc by contact
- Cell-mediated immunity
what do b cells transform into
plasma cells
what do plasma cells do
Kill by secretion of antibodies
Humoral immunity
(FROM B CELLS!!!!)
where is thymus found
superior mediastinum
how many lobes to thymus
2
what happens to thymus at puberty
undergoes involutions
most active frombirth to puberty
function of thymus (3)
1) Provides an environment where T cell precursors proliferate, mature and acquire their immunocompetence.
2) Supplies mature T cells to secondary lymphoid organs.
3) Secretes hormone-like substances which stimulate T cell proliferation and maturation.
major cell types in cortex of thymus
large lymphocytes (immature T)
small lymphocytes (maturing T)
epithelial reticular
macrophages
clonal selection is another term for
maturation
clonal selection
outer cortex large immature lymphocytes proliferate and divide, move through inner to corticomedullary junction. (React with body antigen as moving through or those that cant react die by apoptosis – 95%!!)
positive selection
t cells that recognize non self antigens become mature (helper and cytotoxic) less than 5%
negative selection
React with body antigen as moving through or those that cant react die by apoptosis – 95%!!
Apoptotic T cells are phagocytized by
macrophages - contribute to negative selection
what does negative selection do
prevents development of autoimmune disease
what are epithelial reticular cells linked by
desmosomes
epithelial reticular cells (what do they do)
present antigens to maturing T cells
instruct/educate maturing t cells to react or not react with antigens
thymulin, thymosin, thymopoietin
● Polypeptides secreted by epithelial reticular celThymic hormone-like substances
hassall’s corpuscle
histo marker for thymus
first appear in fetal life and increase in number and size after
concentric layers of epithelial reticular cells
hassall’s corpuscle histo description
Concentric layers of epithelial reticular cells that appear eosinophlic, keratinized and degenerative
* can secrete cytokines and phagocytose
thymic involution
thymus of elderly adult showing lymphoid tissue separated by adipose tissue
already have enough secondary t cells in organs to keep immunity
