Objectives for This Exercise The lymphatic system is vital to
the defense against illness. If infectious agents manage to
breach the mechanical barriers and gain entry to the milieu
interieur, the cells which deal with the invasion are those
which have arisen, developed, matured, and/or been stored in
lymphatic organs. Changes in the histology of lymphatic organs
are important diagnostic criteria. For reasons that should be
obvious, the lymphatic system is intimately related, both
structurally and functionally, to the blood vascular system.
Lymph itself is a clear, slightly yellowish and opalescent fluid
derived from blood. It contains white blood cells, specifically
lymphocytes. Certain specialized organs devoted to processing
and modifying lymph and lymphoid cells are present in all normal
mammals. Lymph starts as blood fluid that is "strained" into the
tissue spaces under the hydrostatic pressure of the pumping
blood. It's drained from the intercellular spaces by thin vein-
like lymphatic vessels, re-enteri