Lymphoid organs Flashcards
Primary lymphoid organs
Where WBCs are produced and mature Bone Marrow Thymus Bursa of Fabricius in Birds Ileal Peyer’s patches near ileocaecal junction (B cells) in ruminants, pigs, horses, dogs and humans
Secondary Lymphoid Organs
Where WBCs reside and ecnounter antigen Lymph nodes Spleen tonsils Mucosa-associated lymphoid tissues (MALT) Haemal nodes (ruminants) Caecal tonsils (birds)
Function of lymphatic tissue
Capture fluid lost from blood Control infection Lymphatic transport
Lymphatic nodules (follicles)
-secondary lymphatic organs and loose connective tissue of the body -densly packed spherical aggregation of lymphocytes; predominantly B cells
Where is red marrow
In flat bones -skull, ribs, sternum, pelvis, vertebrae, heads of long bones
Where is yellow marrow
Found in the shaft of long bones -As the animal ages, adipose tissue replaces the marrow in the long bones.
Structures of the bone marrow stroma
Collagen fibres Reticular fibres - reticular cells, fibroblasts, fat cells, osteogenic cells Stromal elements impact on cell differentiation in the bone marrow
Function of the thymus
differentiation of T lymphocytes Development of immunological tolerance
Structure of the thymus
General structure of the lymph node
Thymic epithelial cells role in immunity
They are antigen presenting cells and are present in positive selection of the thymocytes
Primary B cell follicles contain
Mature maive B cells
Secondary B cell follicles contain
Outer mantle of non proliferating B cells
Inner pale germinal centre containing proliferating and maturing B cells, antigen-presenting follicular dendritic cells and helper T cells
3 Lymph Node regions
Cortex: B cells
Paracortex: T cell rich
Medulla: Blood vessles, sinuses and medullary chords with plasma cells, macrophages and B cells
Entry of lymphocytes into lymph nodes
- 10% from afferent lymph with dendritic cells and macrophages
- 90% from the blood
Species differentiation of porcine lymph nodes
- ‘Inside out’ architecture
- Lymphoid follicles are in the middle of the organ, diffuse lymphoid tissue in the outer zone.
- Afferent lymphatics enter at the hilus
- Effernt lymphatics leave at the node surface
- lymphocytes leave via the blood rather than the lymph
Functions of the spleen
- Clearing particulate and other antigens
- clearing microorganisms
- Clearing aged red cells and remnants of DNA and ribosomes from reticulocytes
- B cell response to bacterial antigens
- Reservoir of RBC and platelets
Spleen white pulp
Periarteriolar lymphoid sheaths (PALS)
Primary and secondary follicles
marginal zome and mantle or corona
Red pulp of spleen
-Filter and trap damaged erythrocytes and associated debri
Animals that hace closed splenic circulation
Cats and dogs
Defensive spleen
Human, primates, mice, rats, rabbits
Limited contractile ability
Extensive periarteriolar lymphoid sheaths, numerous lymphoid follicles
Storage Spleen
Dogs, cats, horses, ruminants and pigs
Capsule and trabeculae have well developed smooth muscle - reservoir for blood
-smaller PALS and fewer lymphoid follicles
Gut-associated lymphoid tissue (GALT)
- Ileal and jejunal Peyers patches in the intestinal wall
- Diffuse lymphoid tissue outside of organised lymphatic structures
- tonsils
- appendix in humans
Mucosa-associated lymphoid tissue (MALT)
contain what cells
- B cell follicles
- plasma cells in diffuse lymphoid tissue
- tonsillar surface is smooth in dogs and cats; horses and ruminants have invaginations and crypts which increase surface area
- No afferent lymph; efferent lymph in tonsillar capsule
