Biomedical Engineering Reference
In-Depth Information
FIGURE 8.3 Structure of a lymph node,
showing the internal arrangement of the
lymph node sinuses. Each lymph node is
associated with one artery and one vein that
provide a direct connection between foreign
particles within the cardiovascular system
and lymphocytes within the lymphatic sys-
tem. Lymph enters the lymph node from
multiple afferent vessels that pass through
various chambers of the lymph node. These
chambers have multiple lymphocytes to
monitor the presence of inflammatory med-
iators. After passing through these cham-
bers, lymph flows out of the lymph node
from one efferent vessel. Adapted from
Martini and Nath (2009).
Efferent
vessel
Lymph node
artery and vein
Medulla
Outer
cortex
Cortex
Afferent
vessel
cortex is typically on the order of 10 to 20 cells in thickness (200 to 400
m). Lymph then
enters the cortex of the lymph node, which surrounds the lymph's artery and vein, con-
necting the lymph node to the circulatory system. The cortex is composed mainly of T-
cells, but many lymphocytes can migrate out of the cardiovascular system into the lymph
nodes at this location. Lymph then continues into the medulla of the lymph node, which
consists primarily of B-cells and plasma cells. The medulla collects lymph entering from
all of the afferent lymphatic vessels and shunts it toward the single efferent lymphatic ves-
sel. At any of these locations within the lymph nodes, lymph comes into contact with
immune cells to help initiate an immune response, if needed. Each lymph node is con-
nected to the cardiovascular system via one artery and one vein.
Lymphatic flow is a pressure-driven flow. The viscosity of lymph is close to that of
water (1 cP). All of the fluid mechanics relationships that we have discussed so far apply
to the lymphatic system. In particular, most of flow scenarios within the lymphatic system
will mimic what is seen in the venous system because of the presence of valves, slow pres-
sure-driven flow, a muscular pumping system, and a large elasticity of the vascular walls.
We will therefore not reiterate the relationships here because they can be found elsewhere
in this textbook.
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8.4 DISEASE CONDITIONS
8.4.1 Cancer Metastasis via the Lymphatic System
Metastasis is the spreading of malignant tumor cells from the primary tumor location to
another location within the body. Before we discuss the role that the lymphatic system
plays in metastasis, it is important to discuss some characteristics of cancer itself. Cancer
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