Chapter 20
The Lymphatic System and Lymphoid Organs and Tissues
757
20
What do all these organs have in common? Except for the
thymus, all are composed of reticular connective tissue. Al-
though all lymphoid organs help protect the body, only the
lymph nodes filter lymph. Te other lymphoid organs and tis-
sues typically have efferent lymphatics draining them, but lack
afferent lymphatics.
Spleen
Te soF, blood-rich
spleen
is about the size of a fist and is the
largest lymphoid organ. Located in the leF side of the abdomi-
nal cavity just beneath the diaphragm, it curls around the ante-
rior aspect of the stomach (±igure 20.5 and
Figure 20.6
). It is
served by the large
splenic artery
and
vein
, which enter and exit
the
hilum
on its slightly concave anterior surface.
Te spleen provides a site for lymphocyte proliferation and
immune surveillance and response. But perhaps even more
5.
What is the benefit of having fewer efferent than afferent
lymphatics in lymph nodes?
For answers, see Appendix H.
Other Lymphoid Organs
Name and describe the other lymphoid organs of the body.
Compare and contrast them with lymph nodes, structurally
and functionally.
Lymph nodes are just one example of the many types of
lymphoid organs
, or aggregates of lymphoid tissue, in the
body. Others are the spleen, thymus, tonsils, and Peyer’s
patches (aggregated lymphoid nodules) of the small intes-
tine
(Figure 20.5)
, as well as bits of lymphoid tissue scat-
tered in the connective tissues.
Splenic artery
Arterioles
and
capillaries
Splenic vein
Hilum
Capsule
Trabecula
Splenic sinusoids
Red pulp
Splenic cords
White pulp
Central artery
Splenic artery
(a) Diagram of the spleen, anterior view
Splenic vein
(b) Diagram of spleen histology
(c) Photograph of the spleen in its normal position in the
abdominal cavity, anterior view.
Diaphragm
Spleen
Adrenal
gland
Splenic
artery
Pancreas
Left
kidney
(d) Photomicrograph of spleen tissue (30
m
).
The white pulp,
a lymphoid tissue with many lymphocytes, is surrounded by
red pulp containing abundant erythrocytes.
Capsule
White pulp
Red pulp
Figure 20.6
The spleen.
(For a related image, see
A Brief Atlas of the Human Body
, Plate 39.)
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