Section VI. 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
6-16. 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).
a. 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.
b. Other lymphoid aggregations are found in the walls of the small intestines.
c. 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.