622
UNIT FOUR
the wall of the thorax, the mammary glands (breasts),
and the upper wall of the abdomen.
3.
Supratrochlear region.
These lymph nodes are located
superF
cially on the medial side of the elbow. They often
enlarge in children in response to infections acquired
through cuts and scrapes on the hands.
4.
Inguinal region.
Lymph nodes in the inguinal region
receive lymph from the lower limbs, the external
genitalia, and the lower abdominal wall.
5.
Pelvic cavity.
Here lymph nodes primarily follow
the iliac blood vessels. They receive lymph from the
lymphatic vessels of the pelvic viscera.
M cells, through which certain ingested molecules pass by
transcytosis, then face lymphocytes and other immune sys-
tem cells that then may initiate an immune response. The
lymphoid tissues in the appendix, Peyer’s patches, tonsils,
adenoids, and mesenteric lymph nodes are collectively
termed mucosa-associated lymphoid tissues (MALT).
Spaces in a lymph node, called
lymph sinuses,
provide
a complex network of chambers and channels through which
lymph circulates. Lymph enters a lymph node through
afferent
lymphatic vessels,
moves slowly through the lymph sinuses,
and leaves through
efferent lymphatic vessels
(F g. 16.10
a
).
Superf
cial lymphatic vessels inF
amed by bacterial in±ection appear
as red streaks beneath the skin, a condition called
lymphangitis.
InF
ammation o± the lymph nodes, called
lymphadenitis,
o±ten ±ollows.
ected nodes enlarge and may be pain±ul.
Locations of Lymph Nodes
Lymph nodes are found in groups or chains along the paths
of the larger lymphatic vessels throughout the body, but they
are not in the central nervous system. The major locations of
the lymph nodes, shown in
f gure 16.11
, are as follows:
1.
Cervical region.
These lymph nodes follow the lower
border of the mandible, anterior to and posterior to the
ears, and deep in the neck along the paths of the larger
blood vessels. These nodes are associated with the
lymphatic vessels that drain the skin of the scalp and face,
as well as the tissues of the nasal cavity and pharynx.
2.
Axillary region.
Lymph nodes in the underarm region
receive lymph from vessels that drain the upper limbs,
Lymphatic
vessels
Blood vessels
Lymph node
Muscle
FIGURE 16.9
Lymph enters and leaves a lymph node through
lymphatic vessels.
FIGURE 16.10
Lymph node. (
a
) A section o± a lymph node. (
b
) Light
micrograph o± a lymph node (20×).
Afferent
lymphatic
vessel
Lymph flow
Subcapsule
(macrophages, B cells)
Sinus
Capsule
Germinal
center
(B cells)
(a)
Nodule
Hilum
Lymph flow
Efferent
lymphatic
vessel
Artery
Vein
Medulla
(macrophages, T cells)
Germinal
center
Capsule
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