lymphoid structures Flashcards
What are the primary lymphoid organs?
Bone marrow (immune cell production, B cell maturation) and Thymus (T cell maturation).
What are the secondary lymphoid organs?
Spleen, lymph nodes, tonsils, adenoids, appendix, Peyer patches. These allow immune cells to interact with antigens.
What are the functions of a secondary lymphoid organ like a lymph node?
Nonspecific filtration by macrophages, circulation of B and T cells, and immune response activation.
Describe the structure of a lymph node.
A secondary lymphoid organ with many afferents and one or more efferents. It is encapsulated with trabeculae.
What is located in the outer cortex of the lymph node?
B-cell localization and proliferation. Primary follicles are dense and quiescent, while secondary follicles have pale central germinal centers and are active.
What is the structure and function of the medulla in a lymph node?
The medulla consists of medullary cords (packed lymphocytes and plasma cells) and medullary sinuses (containing reticular cells and macrophages). The sinuses communicate with efferent lymphatics.
What is the role of the paracortex in a lymph node?
The paracortex contains T cells and is located between the follicles and medulla. It also contains high endothelial venules through which T and B cells enter from blood.
How does the paracortex change in response to an extreme cellular immune response?
In conditions like EBV and other viral infections, the paracortex enlarges (paracortical hyperplasia), leading to lymphadenopathy.
What happens in DiGeorge syndrome regarding the paracortex?
The paracortex is underdeveloped in patients with DiGeorge syndrome.
What happens to the secondary follicles in lymph nodes during an immune response?
Secondary follicles become active, with pale central germinal centers as B cells undergo activation and proliferation.
What are the effects of splenic dysfunction?
Decreased IgM.
Decreased complement activation.
Decreased C3b opsonization.
Increased susceptibility to encapsulated organisms
What are common findings post-splenectomy?
Howell-Jolly bodies (nuclear remnants).
Target cells.
Thrombocytosis (due to loss of sequestration and removal).
Lymphocytosis (due to loss of sequestration).
Why should patients with splenic dysfunction or post-splenectomy be vaccinated?
To protect against encapsulated organisms such as:
Pneumococci.
Haemophilus influenzae type b (Hib).
Meningococci.
What conditions can lead to splenic dysfunction?
splenectomy
ITP
hereditary spherocytosis
functional asplenia (sickle cell anemia )
What are the components of the spleen’s white pulp and their functions?
Periarteriolar lymphatic sheath: Contains T cells.
Follicle: Contains B cells.
Marginal zone: Contains macrophages and specialized B cells. This is the site where antigen-presenting cells (APCs) capture blood-borne antigens for recognition by lymphocytes.
