C irculation o f lym ph • Figure 12.3
Lymph drains from interstitial fluid
through lymphatic capillaries, which
in turn feed into larger lymphatic
vessels and ultimately flow back into
the cardiovascular system. Lymph and
interstitial fluid are chemically similar
to blood plasma but with less protein.
Each day, the lymphatic system returns
about 3 L
(about 15%
) of fluid fi ltered
from blood to maintain blood volume.
Lymphatic ducts
(thoracic
duct, right lymphatic duct)
empty lymph into the junction
of jugular and subclavian veins
of the cardiovascular system.
Lymphatic vessels
pass lymph to
lymphatic ducts.
PULMONARY
CIRCULATION
Efferent lymphatic
vessels
carry lymph
from lymph nodes.
Afferent lymphatic
vessels
carry lymph from
blood capillaries to lymph
nodes.
Lymph nodes
filter
lymph and remove foreign
substances through
filtering, phagocytosis, and
immune reactions.
Lymph
Endothelium
of lymphatic
capillary
Tissue cell
Interstitial
fluid
Anchoring
filament
Opening
Endothelial cells that make up
lymphatic capillaries
overlap like roof shingles.
• When interstitial fluid pressure exceeds lymph pressure
inside, the cells separate slightly, and fluid enters the
capillary like floodwater pushing open a door.
• When the lymph pressure exceeds the interstitial fluid
pressure, the cells close tightly, and lymph cannot
escape back.
Lymphatic
capillaries
Pulmonary
blood
capillaries
Systemic blood
capillaries
Blood plasma is
filtered from blood
capillaries into
interstitial spaces
to become
interstitial fluid.
Venule
Tissue
cell
Blood
Interstitial
fluid
Blood
capillary
Blood
Arteriole
Lymph
Lymphatic
capillary
Let’s take a closer look at the circulation of lymph in
Figure 1 2.3, which shows the relationship of lymphatic
vessels and lymph nodes to the cardiovascular system.
Notice the close-up of the structure of lymphatic cap-
illaries. This overlapping structure allows interstitial
fluid to flow into the lymphatic capillaries—but not out.
Figure 12.3 also shows that afferent lymphatic ves-
sels carry lymph from capillaries to nodes (step fc ), and
that efferent lymphatic vessels carry lymph away from
a node (step K ). Finally, the lymphatic vessels (step C )
empty lymph into the junction of the jugular and subcla-
vian veins of the cardiovascular system. (step ^5 )
As in the venous system, the pressure responsible for
lymph flow is generated by skeletal muscle pumps and re-
spiratory pumps (see Chapter 11).
Components of the Lymphatic System Are Found Throughout the Body
347
p r o c e ss
diagram
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