Lymphoid Organs Lesson 16
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Questions and Answers

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?

<p>mucosa-associated lymphoid tissue (MALT) and encapsulated organs (e.g., lymph nodes, haemolymph nodes, spleen)</p> Signup and view all the answers

What are the areas of active proliferation of B cells in secondary lymphoid follicles?

<p>germinal center</p> Signup and view all the answers

What is the mantle of the secondary lymphoid follicle primarily composed of?

<p>memory B cells</p> Signup and view all the answers

What structures make up the germinal center of the secondary lymphoid follicle?

<p>lymphoblasts, large, medium and small B cells, some T cells, and macrophages</p> Signup and view all the answers

What is the mucosa-associated lymphoid tissue (MALT) responsible for?

<p>protecting the mucosa from pathogens</p> Signup and view all the answers

Where do diffuse lymphocyte infiltrations occur in the mucosa-associated lymphoid tissue?

<p>digestive epithelium and in the lamina propria of the digestive, respiratory, and genitourinary mucosa</p> Signup and view all the answers

What are Peyer's patches made up of?

<p>follicular aggregates located in the lamina propria and submucosa of the small intestine and ileocecal valve</p> Signup and view all the answers

What are the three clearly differentiated regions of Peyer's patches?

<p>dome, lymphoid follicle, and interfollicular area</p> Signup and view all the answers

What are the tonsils partially encapsulated accumulations of?

<p>lymphoid tissue</p> Signup and view all the answers

What type of epithelium lines the tonsils located in the nasopharynx?

<p>columnar pseudostratified epithelium</p> Signup and view all the answers

Where do the lymphoid areas of the tonsils lie?

<p>below the epithelium</p> Signup and view all the answers

What do the interfollicular areas of the tonsils mainly consist of?

<p>T cells</p> Signup and view all the answers

What are the accumulations of lymphoid tissue in the mucosa of the transit zone between the digestive and respiratory systems called?

<p>tonsils</p> Signup and view all the answers

What are the main components of the thymus stroma?

<p>Reticulo-epithelial cells</p> Signup and view all the answers

Where are Hassall's corpuscles located, and what are they formed by?

<p>Located in the medulla, formed by degenerating reticulo-epithelial cells.</p> Signup and view all the answers

What is the function of the Bursa of Fabricius in birds?

<p>Lymphoepithelial organ for B cell genesis and differentiation.</p> Signup and view all the answers

Describe the structure of the Bursa of Fabricius.

<p>It has a mucosa/submucosa, muscular, and serosa, with columnar pseudostratified epithelium and lymphoid follicles.</p> Signup and view all the answers

What is the involution process of the thymus?

<p>The transformation into adipose tissue with few lymphocytes.</p> Signup and view all the answers

What are the components of the secondary lymphoid organs?

<p>Primary and secondary lymphoid follicles, reticular fibers, reticular cells, and follicular dendritic cells.</p> Signup and view all the answers

What is the function of follicular dendritic cells?

<p>Presenting antigens to B cells.</p> Signup and view all the answers

Where do T lymphocytes differentiate and proliferate?

<p>Thymus</p> Signup and view all the answers

What are the two main regions of the thymus, and what is their composition?

<p>Cortex (peripheral, basophilic region) and medulla (central, eosinophilic region), with pseudolobules due to confluent medullary areas.</p> Signup and view all the answers

What is the function of interdigitating cells in the thymus?

<p>They are involved in antigen presentation and T cell activation.</p> Signup and view all the answers

What are the components of the thymus if involution has started?

<p>T cells, macrophages, interdigitating cells, and adipocytes.</p> Signup and view all the answers

What happens approximately two months after birth to the Bursa of Fabricius in birds?

<p>It undergoes involution.</p> Signup and view all the answers

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.

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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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