6.6 Associated Protective Structures

Within the body, there are many structures that aid in protection from bacteria, viruses, and other foreign substances. These structures include cells that can phagocytize (engulf) foreign particles or manufacture antibodies (which help to inactivate foreign substances). Collectively, such cells make up the reticuloendothelial system (RES). Such cells are found in bone marrow, the spleen, the liver, and lymph nodes.

Lymphoid Structures

STRUCTURES WITHIN THE DIGESTIVE SYSTEM

Lymphoid structures make up the largest part of the RES. Lymphoid structures are collections of cells associated with circulatory systems (to be discussed in lesson 9).

Tonsils are associated with the posterior portions of the respiratory and digestive areas in the head, primarily in the region of the pharynx. The tonsils are masses of lymphoid tissue. Other lymphoid aggregations are found in the walls of the small intestines. The vermiform appendix, attached to the cecum of the large intestine, is also a mass of lymphoid tissue. It is the "tonsil" of the intestines.