756
UNIT 4
Maintenance of the Body
20
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.
Homeostatic Imbalance
20.3
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
are called
buboes
(bu
9
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
4.
What is a lymphoid follicle? What type of lymphocyte
predominates in follicles, especially in their germinal centers?
Afferent
lymphatic
vessels
Efferent
lymphatic
vessels
Capsule
Trabeculae
Hilum
Cortex
Lymphoid follicle
Germinal center
Subcapsular sinus
Medulla
Medullary
cord
Medullary
sinus
Follicles
Trabecula
Subcapsular
sinus
Capsule
Medullary
cords
Medullary
sinuses
(b) Photomicrograph of part of a lymph node
(72
m
)
(a) Longitudinal view of the internal structure of a lymph node and
associated lymphatics
Figure 20.4
Lymph node.
In (a), notice that several afferent lymphatics converge on its
convex side, whereas fewer efferent lymphatics exit at its hilum.
Tonsils
(in pharyngeal
region)
Thymus
(in thorax; most
active during youth)
Spleen
(curves around
left side of stomach)
Peyer’s patches
(aggregated lymphoid
nodules in small
intestine)
Appendix
Figure 20.5
Lymphoid organs.
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