Lymphoid tissue and organs, along with lymphatic vessels, constitute a widespread immune defense and 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.

The learning objective for this session are:

1. Identify the architectural and cellular organization of the thymus.
2. Identify the structural architecture and cellular composition of lymph nodes.
3. Identify the non-encapsulated collections of lymphoid tissue associated with the gastrointestinal tract (GALT) and explain their functions: tonsils, Peyer's patches, and appendix.
4. Identify the connective tissue capsule, trabeculae, white and red pulp in spleen and components of the blood circulation in the spleen.
    

The actors.