Lecture 32: Lymphoid Organs and Tissues Flashcards
Lymphoid organs
Primary: Bone Marrow, Thymus
Secondary: Lymph nodes, spleen, MALT (mucosa associated lymphoid tissue)
Bone Marrow gives rise to
T cell precursors and mature B cells.
Where do T cell precursors mature?
In the thymus
Two types of T cells
Helper T cells –> activate cytotoxic t cells
Cytotoxic T cells, kill tumor cells, virus-infected cells, etc by contact
Cell-mediated immunity
Function of B cells
transform into plasma cells. Kill by secretion of antibodies, humoral immunity.
Thymus is active/formed when
Well-formed before birth, active until puberty at which point it turns into fatty mass. Made of two lobes
Thymus anatomy
Two lobes.
Each lobe has lobules.
Each lobule ahs cortex ad medulla.
What are Capsule and CT septa?
Lymphatics of thymus
No afferent lymphatics, but has draining efferent lymphatics which drain the capsule and CT septa.
Layers of lobule of thymus?
Outer cortex –> inner cortex –> medulla
Functions of thymus
Provides an environment where T cell precursors proliferate, mature and acquire their immunocompetence.
Supplies mature T cells to secondary lymphoid organs.
Secretes hormone-like substances which stimulate T cell proliferation and maturation.
how do maturing T-cells die?
Through apoptosis when they are incpable of reacting with any antigens in the thymus, this process is called negative selection. 95% of cells die this way. 5% of cells do recognize an antigen and are fully matured.
How does apoptosis of T-cells happen?
through phagocytosis of macrophages. This eliminates self-reactive T-cells. If you have self-reactive T cells can cause systemic lupus erythematosus (SLE).
epithelial reticular cells purpose
Present antigens to maturing T cells in the thymus, “instruct” maturing T-cells.
What do epithelial reticular cells secrete
hormone-like polypeptide substances. Regulate T-cell proliferation and maturation.
Hassall’s corpuscle
Found in medulla in thymus. Appear as concentric layers of epithelial reticular cells that appear eosinophilic, keratinized and degenerative. Very obvious, looks like pink rose.
Thymic involution
Degeneration of thymus , lymphoid tissue which is separated by adipose tissue, turns very fatty.
MALT (mucosa associated lymphoid tissue) are found where?
Diffuse lymphoid cells in mucosa
Lymphoid follicles in GI, respiratory and genitourinary tracts
Peyers patches of the ileum
tonsils
Intraepithelial lymphocytes
Reside in the intercellular space of enterocytes in the small intestine. Are cytotoxic T-cells. Fall under MALT.
How do plasma cells work in the gut.?
The plasma cells in the lamina propria. Secrete IgA into lumen of gut, this prevents attachment of bacteria/toxins to enterocytes. HOW?
Primary vs. Secondary lymphoid follicle
Primary follicle –> ovoid structures containing aggregates of lymphocytes
Secondary follicles –> follicles containing a central pale area –> germinal center (site of B cell activation)
Peyer’s patches of the ileum contents
Large aggregates of secondary follicles (site of B cell activation). T cells between follicles, B cells localized to within germinal centers within follicles.
M cells
Found in epithelium overlying patches,
