Fundamentals of Anatomy and Physiology

The Lymphatic Circulatory System 355

Germinal center

Capsule

Sinuses^

Afferent lymph

vessel

Cortical

nodules

Hilum

Trabeculae

Efferent

lymph vessel

(^) ®
Learning
Cengage
2016 ©
Figure 15- 5 Internal anatomy of a lymph node showing germinal centers and
sinuses.
positions on the node and the lymph passes through the
sinuses of the nodes. In the node, antigenic micro-
organisms, foreign substances, or cancer cells stimulate
lymphocytes to divide, and the immune response is ac-
tivated. Macrophages phagocytize the attacked foreign
substances. Efferent vessels leave nodes and pass on to
other lymph nodes by either going with other afferent
vessels into another node of the same group or passing on
to another group of nodes. The efferent vessels will
eventually unite to form lymphatic trunks.
This circulation of lymph through the various lym-
phatic vessels is maintained by normal skeletal muscle
contractions. This action compresses the lymphatic ves-sels
and because those vessels have one-way valves, the
compression forces the lymph in one direction toward the
subclavian veins. Normal movement helps circulate the
lymph. Another factor in lymph circulation is respi-ratory
or breathing movements, which cause pressure changes in
the thorax. Finally, smooth muscle contrac-tion in the
lymphatic vessel also pushes lymph along.
Common Disease, Disorder, or Condition
ELEPHANTIASIS
In Africa, the bite of a mosquito can transmit a microscopic filarial nematode worm
known as Wuchereria bancrofti. This nematode worm lives in lymphatics and lymph
nodes where it reproduces and multiplies. After many years of continuous reinfec-tions,
the lymphatic system gets blocked, resulting in tremendous swelling of the arms or legs.
This swelling or edema results in a condition known as elephantiasis. In addition to the
limbs, the scrotum can also be affected, resulting in an almost basketball-like swelling of
the scrotum or testicles. The disease also occurs in Malay-sia but is caused by another
nematode worm known as Brugia malayi. In that part of the world, only the limbs show
the characteristic swelling of the disease.