Biomedical Engineering Reference
In-Depth Information
is a disease that is characterized by uncontrollable cell division. This is typically caused by
a destruction and/or modification of some of the genes within the cell. If the rate of cell
division exceeds the rate of cell death, then a tumor forms. Tumors are defined as a mass
of abnormally dividing cells. Tumors can be benign, which rarely lead to death, or malig-
nant, which are cells that no longer function normally.
The primary tumor is the location where the first cells started to divide uncontrollable.
As this process continues, the tissue becomes exceedingly large and it cannot contain all of
the tumor cells within that space. Metastasis occurs when tumor cells break away from the
primary tumor and invade other nearby locations of the body. To do this, tumor cells
migrate through the interstitial space. Once in the interstitial space, tumor cells can be
taken into the lymphatic system or enter the bloodstream. Regardless of which capillary
(blood or lymphatic) the tumor cells enter, they can now be carried throughout the body
relatively easily. This initiates secondary tumor sites, which are difficult to locate and diffi-
cult to treat. Once the tumor cell has exited the lymphatic system or blood vessels and has
reestablished itself in a new location, this location is defined as the secondary tumor site.
If tumor cells have penetrated the lymphatic system, it is also typical for them to amass
within lymph nodes, preventing immune cells from recognizing invading particles. It is
then likely for a patient to succumb to an infection because the inflammatory process will
not proceed normally.
If the cancer cells enter the bloodstream, they can also be carried to other locations
within the body to establish secondary tumors. Tumor cells use a great deal of energy at
the expense of the surrounding healthy tissue. To accommodate this new demand, cancer
cells have the ability to stimulate new blood vessel growth (or angiogenesis). The addi-
tional blood supply unfortunately acts to accelerate the rate of cancer cell growth and does
not provide the healthy tissue with the nutrients it needs. This leads to the death of nor-
mal cells and tissue/organ malfunction due to a lack of nutrients. Also, the simple com-
pression of a large mass of tumor cells on a healthy organ causes the organ to not function
properly. Cancer is a disease that is intimately associated with the cardiovascular system,
and currently there is not a great deal of information available on how tumor cells interact
and use the cardiovascular system to its advantage.
8.4.2 Lymphedema
Lymphedema is very similar to edema associated with microvascular networks.
Typically, a lymphatic vessel becomes blocked, and this prevents lymph from passing
through the lymphatic system and being returned to the cardiovascular system. In this sce-
nario, lymph collects within the lymphatic vessel and interstitial fluid collects within the
interstitial space. The region upstream of the blocked lymphatic vessel becomes swollen
because fluid cannot pass through the blockage. The danger of lymphedema is associated
with an infectious outbreak due to the decrease in lymph flow. Because a major initiator of
the inflammatory response is associated with the lymph tissues and organs, it is likely that
during lymphedema, infectious agents never arrive at these tissues and organs. Because
the interstitial fluid and lymph is also stagnant, it is unlikely that many white blood cells
will be in the vicinity of the infectious agents. Therefore,
the infectious agents can
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