9. Lymphoid system Flashcards
what happens in the bone marrow and thymus in terms of binding capacity?
lymphocytes with binding capacities for own proteins are eliminated
what do t cells act via?
cytokines or cell death inducing agents
types of antigen presenting cells
what do they do
macrophages
dendritic cells
Phagocytose intruders and remnants of disintegrated cells.
Fragment ingested proteins and present those fragments on MHC on surface
(Major Histocompatibility Complex)
types of effector cells
all types of b and t cells (including plasma)
what are matching venules and how can they be distinguished in histology?
secondary lymphoid system
- aggregates of thousands of lymphocytes.
- are the principle sites of antigen presentation and T- and B cell activation and expansion
- are kept in shape by a network of fine reticular fibres that allow lymphocytes and APCs to circulate around them.
- have stretches of blood vessels with broadened epithelia for entry/exit of travelling lymphocytes.
where are lymph nodes found?
just underneath epithelia. frequent in airways and digestive tract
what are tonsils?
aggregates of lymph follicles in partial collagen capsule deep to oral and nasal cavity epitherlium- forms a ring around pharynx
what are lymph nodes?
Encapsulated aggregates of follicles.
what is the course of fluid from capillaries to lymph system?
The capillary system is slightly “leaky”.
Liquid pressed into the interstitial tissue is collected inlymph capillaries, which congregate into ever larger lymph vessels,
eventually end up in subclavian veins.
In between are lymph nodes, where lymph is checked by APCs.
red: corticol zone - area of B cell maturation and proliferation
green: Paracortical zone: Area of T cell activation and proliferation. This area contains the majority of APCs in the node.
yellow:
Medulla: High concentration of plasma cells. Also macrophages for cleanup or holding undigestable material.
adaptive response
antigen carriage by dendritic cells to lymphoid tissue
activation of specific T and B lymphocytes and Ab production recirculation to site of infection
GC: germinal centre
MZ: mantle zone
GC:
characterise secondary follicles in the cortex.
areas of B cell maturation, in which some of the activated B cells die off.
The others differentiate to a majority into plasma cells, a minority into memory cells.
At higher magnification, large, paler nuclei are visible. They represent follicular dendritic cells which hold and present antigen during this maturation process. Germinal centres indicate an active B cell response.
how do lymphocytes find their target?
Paracortical zone with high endothelial venules
Lymphocytes travel constantly between lymph nodes and other secondary lymph organs in search of a matching antigen.
Lymphocytes can and do travel in the lymph vessels, but the majority (~90%) travels in the bloodstream.
They enter the lymph nodes at the sites of high endothelial venules (V, arrows), normally located in the paracortex, which have cuboidal endothelia, in contrast to normal venules, where the endothelium is squamous. Most leave via the efferent lymph vessels from where they will eventually enter the bloodstream again.
