Biomedical Engineering Reference
In-Depth Information
Chapter 7
Vessel Wall
Blood and lymphatic vessels form networks for the transport of fluids, gases,
macromolecules, particularly nutrients and signaling compounds, and circulating
cells between the body's tissues. The lymphatic network is involved in the immune
surveillance of the body. Lymphocytes and antigen-presenting dendritic cells
travel through lymphatics between peripheral tissues and lymphoid organs, where
immunocytes mature.
Blood and lymphatic networks are connected by left and right lymphatic ducts
that drains lymph into blood circulation.
Left lymphatic duct
,
1
or the
thoracic duct
,
is the largest lymphatic vessel (length 38-45 cm; diameter
5 mm). It originates in
the abdomen from the confluence of the right and left lumbar and intestinal trunks to
terminate close to the junction of the left subclavian and left internal jugular veins.
Lymph from the right arm, right region of the thoracic cavity, right side of the neck
and head, and possibly lower left lobe of the left lung, is collected by the
right
lymphatic duct
(length
∼
12.5 mm), which commonly ends in the right subclavian
vein, near its junction with the right internal jugular vein.
Both vascular structures are lined with endothelial cells that acquire tissue-
specific specialization (Chap.
9
). Endothelium ensures formation, maintenance,
growth, and repair of vessel walls (Chap.
10
).
∼
7.1
Physical Environment
Vascular cells adapt to mechanical stimuli and remodel, thereby changing ge-
ometry, structure, and properties. Major stresses applied to blood vessels in-
clude: (1) axial stress induced by longitudinal tension; (2) circumferential stress
(
c
θ
=
p
i
R
i
/
h
;
R
i
: internal hydraulic radius;
h
:wall thickness [Laplacian equation for
1
A.k.a. alimentary duct, chyliferous duct, and Van Hoorne's canal.
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