620
UNIT FOUR
Lymph also returns to the bloodstream most of the small
proteins that the blood capillaries F ltered. At the same time,
lymph transports foreign particles, such as bacteria and
viruses, to lymph nodes.
Lymphatic capillaries are adapted to receive proteins and
foreign particles in a way that blood capillaries are not. The
epithelial cells that form the walls of lymphatic vessels over-
lap but are not attached to each other. This conF guration,
shown in
f
gure 16.8
, creates fl
aplike valves in the lymphatic
capillary wall. The valves are pushed inward when the pres-
sure is greater on the outside of the capillary but close when
the pressure is greater on the inside.
The epithelial cells of the lymphatic capillary wall are
also attached to surrounding connective tissue cells by thin
protein F laments. As a result, the lumen of a lymphatic capil-
lary remains open even when the outside pressure is greater
than the pressure inside the lymph capillary.
PRACTICE
4
What is the relationship between tissue f
uid and lymph?
5
How do plasma proteins in tissue f
uid aF
ect lymph ±ormation?
6
What are the major ±unctions o± lymph?
the tissue fl
uid hydrostatic pressure moving tissue fl uid into
lymphatic capillaries, forming lymph. Thus, lymph forma-
tion prevents the accumulation of excess tissue fluid, or
edema
(e
˘
de-mah).
Lymph Function
Lymphatic vessels in the small intestine play a major role
in the absorption of dietary fats (chapter 17, pp. 684–685).
Area drained
by right lymphatic duct
Right lymphatic
duct
Lymphatic
trunks
Lymph nodes
Lymphatic
vessels
Thoracic duct
Cisterna
chyli
Thoracic duct
Left internal
jugular vein
Left subclavian
vein
Axillary lymph
nodes
Right subclavian
vein
Right lymphatic duct
Right internal jugular vein
Lymphatics of
mammary gland
(a)
(b)
Lymphatic capillary
Afferent lymphatic vessel
Lymph node
Lymphatic trunk
Collecting duct
Subclavian vein
Efferent lymphatic vessel
FIGURE 16.6
Lymphatic pathways. (
a
) The right lymphatic duct
drains lymph ±rom the upper right side o± the body, whereas the
thoracic duct drains lymph ±rom the rest o± the body. (
b
) Lymph
drainage o± the right breast illustrates a localized ±unction o± the
lymphatic system. Surgery to remove a cancerous breast can disrupt
this drainage, causing pain±ul swelling.
FIGURE 16.7
The lymphatic pathway.
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