28 Questions
What are the two primary lymphoid organs in mammals?
bone marrow and thymus
What is the function of the lymphoid system?
to protect the animal body against biological agents and molecules
What is the parenchyma of the lymphoid system made up of?
lymphocytes
What are the two groups of secondary lymphoid organs mentioned in the text?
mucosa-associated lymphoid tissue (MALT) and encapsulated organs (e.g., lymph nodes, haemolymph nodes, spleen)
What are the areas of active proliferation of B cells in secondary lymphoid follicles?
germinal center
What is the mantle of the secondary lymphoid follicle primarily composed of?
memory B cells
What structures make up the germinal center of the secondary lymphoid follicle?
lymphoblasts, large, medium and small B cells, some T cells, and macrophages
What is the mucosa-associated lymphoid tissue (MALT) responsible for?
protecting the mucosa from pathogens
Where do diffuse lymphocyte infiltrations occur in the mucosa-associated lymphoid tissue?
digestive epithelium and in the lamina propria of the digestive, respiratory, and genitourinary mucosa
What are Peyer's patches made up of?
follicular aggregates located in the lamina propria and submucosa of the small intestine and ileocecal valve
What are the three clearly differentiated regions of Peyer's patches?
dome, lymphoid follicle, and interfollicular area
What are the tonsils partially encapsulated accumulations of?
lymphoid tissue
What type of epithelium lines the tonsils located in the nasopharynx?
columnar pseudostratified epithelium
Where do the lymphoid areas of the tonsils lie?
below the epithelium
What do the interfollicular areas of the tonsils mainly consist of?
T cells
What are the accumulations of lymphoid tissue in the mucosa of the transit zone between the digestive and respiratory systems called?
tonsils
What are the main components of the thymus stroma?
Reticulo-epithelial cells
Where are Hassall's corpuscles located, and what are they formed by?
Located in the medulla, formed by degenerating reticulo-epithelial cells.
What is the function of the Bursa of Fabricius in birds?
Lymphoepithelial organ for B cell genesis and differentiation.
Describe the structure of the Bursa of Fabricius.
It has a mucosa/submucosa, muscular, and serosa, with columnar pseudostratified epithelium and lymphoid follicles.
What is the involution process of the thymus?
The transformation into adipose tissue with few lymphocytes.
What are the components of the secondary lymphoid organs?
Primary and secondary lymphoid follicles, reticular fibers, reticular cells, and follicular dendritic cells.
What is the function of follicular dendritic cells?
Presenting antigens to B cells.
Where do T lymphocytes differentiate and proliferate?
Thymus
What are the two main regions of the thymus, and what is their composition?
Cortex (peripheral, basophilic region) and medulla (central, eosinophilic region), with pseudolobules due to confluent medullary areas.
What is the function of interdigitating cells in the thymus?
They are involved in antigen presentation and T cell activation.
What are the components of the thymus if involution has started?
T cells, macrophages, interdigitating cells, and adipocytes.
What happens approximately two months after birth to the Bursa of Fabricius in birds?
It undergoes involution.
Study Notes
- The thymus is a lobed parenchymal organ where T lymphocytes differentiate and proliferate independently of antigenic stimulation.
- Thymus development begins prenatally and is composed of lobes surrounded by a thin capsule of connective tissue.
- Each lobe contains cortex (peripheral, basophilic region) and medulla (central, eosinophilic region), with pseudolobules due to confluent medullary areas.
- Reticulo-epithelial cells make up the thymus stroma, providing mechanical support and producing polypeptides for T cell differentiation.
- Thymus contains T cells, macrophages, interdigitating cells, and adipocytes if involution has started.
- Hassall's corpuscles, located in medulla, are formed by degenerating reticulo-epithelial cells.
- The cortex contains large lymphocytes (immature T cells) and macrophages, with subcapsular proliferation and apoptosis of non-recognized cells.
- Medulla consists of differentiated T cells, macrophages, and interdigitating cells, with a continuous capillary blood-thymus barrier preventing contact with antigens.
- The thymus undergoes involution, transforming into adipose tissue with few lymphocytes.
- The Bursa of Fabricius in birds is a lymphoepithelial organ for B cell genesis and differentiation, shaped like a rounded sac communicating with the cloaca.
- The Bursa has a mucosa/submucosa, muscular, and serosa, with columnar pseudostratified epithelium and lymphoid follicles.
- The follicles contain cortex and medulla, with lymphocytes and epithelial reticular cells.
- The Bursa undergoes involution approximately two months after birth.
- Secondary lymphoid organs contain primary and secondary lymphoid follicles, formed by reticular fibers, reticular cells, and follicular dendritic cells.
- Primary follicles have a spherical or ovoid structure, with reticular fibers, reticular cells, and follicular dendritic cells, providing a framework for unstimulated and memory B cells and some T cells.
- Follicular dendritic cells have an euchromatic nucleus and cytoplasmic processes, presenting antigens to B cells.
Test your knowledge about the lymphoid system and its organs, which play a key role in protecting the body against biological agents through the immune response.
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