Journal of Community Nursing - page 45

JCN
2013,Vol 27, No 4
45
WOUND CARE
against gravity, which can cause it to
flow backwards. When this happens,
one-way valves present in the veins
close to prevent backflow of blood
(Anderson, 2006; 2008) (
Figure 3
).
The movement of blood towards
the heart from the lower limbs is
encouraged by gravity when lying
down or when the legs are elevated,
breathing and, importantly, through
the action of the calf-muscle pump
(
Figure 4
).
THE CALF-mUSCLE PUmP
The blood in the leg veins is pushed
upwards partly by the action of the
foot and by the calf muscle pump as
the leg moves (Lindsay et al, 2003).
When the leg moves, the calf muscle
contracts and squeezes the deep vein,
opening the valves and forcing the
blood up towards the heart. As the
calf muscle relaxes, the valves close
and create a negative pressure as
the section between valves empties.
This negative pressure draws blood
from the superficial veins, through
the perforators to refill the chamber
ready for the next contraction of
the calf muscle (Meissner et al,
2007). This mechanism, which again
sends blood upwards, is particularly
important in the legs, because
when standing, blood has to travel a
long way against gravity to return to
the heart.
THE LymPHATIC SySTEm
The lymphatic system has an
important role in maintaining fluid
balance. It carries excessive tissue
fluid, fats absorbed from the digestive
system and proteins that leak from
the capillaries back to the general
circulation, otherwise they would
accumulate in the tissues as oedema
(Starr et al, 2008).
The fluid that circulates the
lymphatic system is known as lymph
and has an important immunological
function — carrying foreign particles
and cellular debris to the lymph
nodes (Starr et al, 2008).
Lymph capillaries are present in
the tissues of all organs. They have
no open end in the tissues, and
extracellular fluid simply diffuses
into the vessels through gaps in the
capillary wall (Starr, 2008).
Like veins, lymph vessels also
have smooth muscle in their walls
and flap-like valves that prevent
backflow. Breathing and movement of
muscle helps to move lymph through
the lymphatic system.
Lymph nodes are located at
intervals along the lymph vessels.
Macrophages within the node help
to clear the lymph of bacteria, debris
and other substances. All lymph
passes through at least one node
before being delivered to the blood
stream.
Lymph vessels converge into
collecting ducts that drain into the
veins in the lower neck. Here, the
cleansed lymph fluid is returned to
the circulation (Starr et al, 2008).
HOW THE vENOUS AND
LymPHATIC SySTEmS WORK
TOGETHER
As blood passes through the capillaries
— a process known as filtration — fluid
leaks out through the semi-permeable
walls and into the interstitial space
that lies between the capillary wall
and the tissues.This fluid is known
as interstitial fluid.The exchange of
nutrients, waste, fluid, electrolytes,
and proteins from the vascular and
lymphatic systems and tissue cells
occur in the interstitial fluid.
When the venous and lymphatic
systems are working correctly, the
direction of fluid movement between
the tissues and the blood and
lymphatic systems is balanced, but
when disease is present, fluid collects
and results in oedema.
WHy DO SKIN CHANGES
OCCUR WITH vENOUS AND
LymPHOvENOUS DISEASE?
If the valves in the veins are damaged
(e.g. due to surgery or trauma), or not
working correctly (e.g. due to disease),
blood will flow back down into the
veins leading to an increase in blood
volume and pressure (
Figure 5
). As a
result of this venous insufficiency, the
walls of the vein stretch and the pores
in the capillary wall enlarge, allowing
fluid, red cells and protein to leak
out into the tissues. It is this process
that causes some of the signs and
symptoms seen as skin changes, such
as hyperpigmentation and oedema
(
Figure 5
). Prolonged leakage can
Figure 3.
One way valves in the veins of the leg
prevent the backflow of blood.
Figure 4.
Action of the calf-muscle pump.
Figure 2.
The veins of the lower limb.
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