Hematopoietic and Lymphoid Tissues

This chapter discusses the hematopoietic and lymphoid tissues. The lymph nodes are peripheral organs that house a major subset of mature lymphoid cells. The lymph nodes serve a similar function in the mouse and human and are critical in mediating immune reactions to exogenous and endogenous stimuli. The lymph nodes in mice are generally very small (1-4 mm) and difficult to visualize within fat or other tissues. They are usually grayish in color and elongated or round. The largest lymph nodes are generally the mesenteric and mandibular nodes. Human lymph nodes are present in typical external locations, including neck (cervical), axillae, and inguinal regions, and also internal locations, including thoracic, para-aortic, and mesenteric regions. Human lymph nodes vary in size from 0.5 to 2 cm. Even in healthy humans, external lymph nodes are often palpable. The lymph nodes are important components of the immune system, and their macroanatomy is similar in mice and humans. © 2012