Biomedical Engineering Reference
In-Depth Information
8.3
Lymph flows through the lymphatic system at a rate of approximately 125 mL/hour for a
total of approximately 3 L of lymph formed per day. This is approximately 60% of the aver-
age blood volume, and this would account for a significant loss of body fluids per day if it
was not returned to the cardiovascular system. The principal regulator of lymph flow is the
interstitial hydrostatic pressure, because the lymphatic system is also under a very low pres-
sure throughout the entire system. Small changes in the interstitial pressure can have a sig-
nificant effect on lymph flow through lymphatic vessels. Lymph is also propelled through
the lymphatic vessels by compression of surrounding tissue (e.g., muscle contraction). Lastly,
lymph must flow through lymph nodes, prior to being returned to the cardiovascular sys-
tem. As lymph enters the lymph node, it passes through many sinuses that contain multiple
lymphocytes to investigate the cells within the lymph. These cells can initiate an inflamma-
tory response if they come into contact with pathogens.
8.4
Two diseases that are associated with the lymphatic system are cancer and edema.
Cancerous cells can easily enter the lymphatic system and then move to other locations
within the body. This would possibly initiate a secondary tumor site somewhere else in the
body. Interestingly, tumor cells can metastasize through the lymphatic system or the cardio-
vascular system. Lymphedema is similar to edema and is defined as an increase in extravas-
cular space water volume (and pressure) due to a blockage or a defect of the lymphatic
system. This can potentially cause a large inflammatory response because it is possible that
pathogens do not come into contact with lymphocytes in the lymphatic tissues.
HOMEWORK PROBLEMS
8.1
What type of blood vessels do the lymphatic vessels most closely match? Are the functions
of these two vessels similar?
8.2
Which lymphatic organ removes damaged red blood cells from circulation? What other func-
tions does this organ have?
8.3
Describe the differences between the deep lymphatic vessels and the superficial lymphatic
vessels.
8.4
What functions do the T-lymphocytes and the B-lymphocytes perform?
8.5
Why is the protein concentration in lymph typically more concentrated than interstitial
fluid?
8.6
Lymphatic vessels have valves that prevent the movement of lymph back toward the capil-
lary beds. What will happen to water movement across the capillary wall if the lymphatic
valves are not functioning properly?
8.7
Approximate the flow rate through a lymphatic vessel with a radius of 75
m, a pressure dif-
ference of 5 mmHg, and an overall length of 1 mm. The viscosity of lymph in this section of
lymphatic vessels is 1.1 cP. If a muscle surrounding the lymphatic vessel constricts the vessel
so that the radius reduces to 25
µ
m and the pressure difference increases to 25 mmHg, what
does the flow rate become under these conditions?
µ
8.8
There are no active pumping mechanisms to propel lymph movement through a lymph
node, which is composed of many interconnected chambers. Discuss the movement of lymph
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