Lymphoid tissue and organs, along with the lymphatic vessels constitute a very widespread and extremely important immune defense system and a filtering system between the body tissues (where foreign substances and organisms can gain entrance) and the blood stream. The structure of lymphatic vessels was considered with the circulatory system in a previous exercise.

This laboratory exercise will deal primarily with lymphoid tissue, which consists of distinct lymphoid organs (the lymph nodes, thymus, and spleen) as well as more diffuse collections of lymphocytes (nodules), which are primarily located along the mucosa of the digestive and respiratory tracts.

Learning Objectives:

• Understand that lymphoid organs show a network of reticular fibers or epithelial tissue filled with lymphocytes and other cells of the immune system.
• Distinguish and recognize the specific unique structural features and regions of lymph nodes, spleen, and thymus and understand the functional significance of these features in each.
• Understand the circulation through the lymph nodes and spleen and how these organs filter lymph and blood respectively.
• Recognize the major unencapsulated collections of lymphocytes in the mucosa-associated lymphoid tissue (MALT), including tonsils, Peyer’s patches, and appendix.

The actors.