Biomedical Engineering Reference
In-Depth Information
Chapter 9
Vascular Endothelium
Vascular endothelium constitutes the interface between the flowing blood and the
deformable solid wall. The endothelium is a thin layer of connected and anchorage-
dependent cells that are subjected to chemical, physical, and mechanical stimuli.
They are directly exposed to molecules that circulate in the blood stream.
Vascular endothelium has several functions, as it is involved in: (1) blood-
wall exchange control; (2) vasomotor tone modulation;
1
(3) coagulation regulation;
(4) vessel wall growth and remodeling; and (5) inflammation and immune defense
owing to leukocyte adhesion and transmigration [
841
]. Last, but not least, vascular
endothelium is required for angiogenesis (Sect.
10.2
). During angiogenesis, the
arteriovenous differentiation drives vessel maturation.
Although endothelial cells of blood and lymph vessels share many features
(strong apicobasal polarity and expression of certain endothelial markers), they
are specialized according to vessel function and convected fluid loading. The en-
dothelium of terminal lymphatics lacks a continuous basement membrane and
intercellular spaces are not tightly sealed by junctional complexes.
Fluorescent plant virus can be used to image small-bore vessels of the
macrocirculation in deep tissues using fluorescence microscopy [
842
], as virus
is incorporated in vascular endothelial cells. This technique identifies arterial and
venous compartments, as fluorescent virus uptake in the veins occurs at a much
higher rate than in the arteries.
The semi-permeable endothelial barrier acts in molecule exchange between
blood and vessel wall or interstitial space of perfused tissues (Sect.
9.6
), thereby reg-
ulating tissue fluid homeostasis. Endothelial permeability of transported molecules
depends on molecular size as well as intercellular junction nature and pattern. This
size-selective transport governs fluid balance of tissues.
1
Among vascular endothelium's active functions, the secretion and modification of vasoactive
substances induce contraction and relaxation of adjoining vascular smooth myocytes (Chap.
8
,
Sect.
8.5.8
).
Search WWH ::
Custom Search