Tunica intima of blood vessel in general
Tunica intima: the innermost layer of the blood vessel.
Tunica intima consists of three components:
1.
Endothelium with its basement membrane
2.
the sub-endothelial connective tissue layer
3.
Internal elastic membrane
Endothelium with its basement membrane:
1.
A single layer of squamous epithelial cells and the
basal lamina of the endothelial cells (a thin extracellular layer composed
chiefly of collagen, proteoglycans, and glycoproteins). The squamous cells of endothelium
are polygonal, oval, or fusiform, and have very distinct round or oval nuclei.
This endothelium is brought into view most
distinctly by staining with silver nitrate.
Several
well-characterized markers are employed to identify ECs, including vascular
endothelial cadherin, platelet endothelial cell adhesion molecule 1, vascular
endothelial growth factor receptors (VEGFRs), and isolectinB4.
During
development, most Endothelial Cells derive from the lateral plate mesoderm, and
through the process of vasculogenesis, primitive Endothelial Cells coalesce
into the initial blood vessel tubes . Subsequently, these initial Endothelial Cell
tubes give rise to further vessels
through angiogenesis, a multistep process consisting of Endothelial Cells
proliferation, migration, invasion, lumen formation, and tube stabilization.
The sub-endothelial
connective tissue layer
- It is consisting
of loose connective tissue. Occasional smooth muscle cells are found in
the loose connective tissue. In arteries of less than 2 mm in diameter. The thickness
is depend on the size of blood vessel.
3.
An elastic or fenestrated layer, which consists of a membrane containing a network
of elastic fibers, having principally a longitudinal direction, and in which,
under the microscope, small elongated apertures or perforations may be seen,
giving it a fenestrated appearance. It was therefore called by Henle the fenestrated
membrane. This membrane forms the chief thickness of the inner coat, and
can be separated into several layers, some of which present the appearance of a
network of longitudinal elastic fibers, and others a more membranous character,
marked by pale lines having a longitudinal direction. In minute arteries the
fenestrated membrane is a very thin layer; but in the larger arteries, and
especially in the aorta, it has a
considerable thickness.
Internal elastic
membrane:
It is a sheetlike layer or lamella of fenestrated
elastic material present within the subendothelial layer of the intima in
arteries and arterioles, is called the internal elastic membrane. Fenestrations
enable substances to diffuse readily through the layer and reach cells deep
within the wall of the vessel
Presence of internal
elastic lamina :
Internal elastic
lamina is present in medium sized
artery, large sized arterioles , and occationally present in large and medium
sized vein
In elastic or large
artery it is present but cannot seen clearly.
Absence of internal
elastic lamina:
It is absent in small
sized arteriole, most of the veins
In dissection, the inner coat (tunica intima) can be separated from
the middle (tunica media) by a little maceration, or it may be stripped off in
small pieces; but, because of its friability, it cannot be separated as a
complete membrane. It is a fine, transparent, colorless structure which is
highly elastic, and, after death, is commonly corrugated into longitudinal
wrinkles.
Difference between tunica intima of large artery and vein
|
Tunica intima of
large artery |
Tunica intima of
large vein |
|
Lined by short,
polygonal endothelial cells. The subendothelial connective tissue is
fi broelastic connective tissue which is thicker than the large vein and
houses some longitudinally disposed smooth muscle cells.
|
The endothelium
with relatively thicker amount of subendothelial connective tissue are
always present. |
|
Internal
elastic lamina is present but not clearly defined. |
Occasionally,
a thin internal elastic lamina is observed |
|
Valves are absent |
Valves are present |
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