Maintenance of the Body
stagnates somewhat, allowing time for the lymphocytes and
macrophages to carry out their protective functions. Lymph
passes through several nodes before it is completely cleansed.
Sometimes lymph nodes are overwhelmed by the agents they
are trying to destroy. For example, when large numbers of bac-
teria are trapped in the nodes, the nodes become inﬂamed,
swollen, and tender to the touch, a condition o±en referred to
(erroneously) as swollen “glands.” Such infected lymph nodes
bōz). (Buboes are the most obvious symp-
tom of bubonic plague, the “Black Death” that killed much of
Europe’s population in the late Middle Ages.)
Lymph nodes can also become secondary cancer sites, par-
ticularly when metastasizing cancer cells enter lymphatic ves-
sels and become trapped there. Cancer-inﬁltrated lymph nodes
are swollen but usually not painful, a fact that helps distinguish
cancerous nodes from those infected by microorganisms.
Check Your Understanding
What is a lymphoid follicle? What type of lymphocyte
predominates in follicles, especially in their germinal centers?
(b) Photomicrograph of part of a lymph node
(a) Longitudinal view of the internal structure of a lymph node and
In (a), notice that several afferent lymphatics converge on its
convex side, whereas fewer efferent lymphatics exit at its hilum.
(in thorax; most
active during youth)
left side of stomach)
nodules in small