The Lymphatic System and Lymphoid Organs and Tissues
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
Te soF, blood-rich
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
). It is
served by the large
, which enter and exit
on its slightly concave anterior surface.
Te spleen provides a site for lymphocyte proliferation and
immune surveillance and response. But perhaps even more
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
Lymph nodes are just one example of the many types of
, 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-
, as well as bits of lymphoid tissue scat-
tered in the connective tissues.
(a) Diagram of the spleen, anterior view
(b) Diagram of spleen histology
(c) Photograph of the spleen in its normal position in the
abdominal cavity, anterior view.
(d) Photomicrograph of spleen tissue (30
The white pulp,
a lymphoid tissue with many lymphocytes, is surrounded by
red pulp containing abundant erythrocytes.
(For a related image, see
A Brief Atlas of the Human Body
, Plate 39.)