The tunica media (
New Latin
New Latin (also called Neo-Latin or Modern Latin) is the revival of Literary Latin used in original, scholarly, and scientific works since about 1500. Modern scholarly and technical nomenclature, such as in zoological and botanical taxonomy ...
"middle coat"), or media for short, is the middle
tunica (layer) of an
artery or
vein
Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenat ...
. It lies between the
tunica intima on the inside and the
tunica externa
The tunica externa (New Latin "outer coat"), also known as the tunica adventitia (New Latin "additional coat"), is the outermost tunica (layer) of a blood vessel, surrounding the tunica media. It is mainly composed of collagen and, in arteries, i ...
on the outside.
Artery
Tunica media is made up of
smooth muscle cells,
elastic tissue and
collagen. It lies between the
tunica intima on the inside and the
tunica externa
The tunica externa (New Latin "outer coat"), also known as the tunica adventitia (New Latin "additional coat"), is the outermost tunica (layer) of a blood vessel, surrounding the tunica media. It is mainly composed of collagen and, in arteries, i ...
on the outside.
The middle coat (tunica media) is distinguished from the inner (tunica intima) by its color and by the transverse arrangement of its fibers.
* In the ''smaller arteries'' it consists principally of smooth muscle fibers in fine bundles, arranged in
lamellæ and disposed circularly around the vessel. These lamellæ vary in number according to the size of the vessel; the smallest arteries having only a single layer, and those slightly larger three or four layers - up to a maximum of six layers.
It is to this coat that the thickness of the wall of the artery is mainly due.
* In the ''larger arteries'', as the
iliac,
femoral, and
carotid,
elastic fibers
Elastic fibers (or yellow fibers) are an essential component of the extracellular matrix composed of bundles of proteins (elastin) which are produced by a number of different cell types including fibroblasts, endothelial, smooth muscle, and air ...
and collagen
unite to form lamellæ which alternate with the layers of smooth muscular fibers; these lamellæ are united to one another by elastic fibers which pass between the smooth muscular bundles, and are connected with the fenestrated membrane of the inner coat.
* In the ''largest arteries'', as the
aorta
The aorta ( ) is the main and largest artery in the human body, originating from the left ventricle of the heart and extending down to the abdomen, where it splits into two smaller arteries (the common iliac arteries). The aorta distributes o ...
and
brachiocephalic, the amount of elastic tissue is considerable; in these vessels a few bundles of white connective tissue also have been found in the middle coat. The muscle fiber cells are arranged in 5 to 7 layers of circular and longitudinal smooth muscle with about 50μ in length and contain well-marked, rod-shaped
nuclei, which are often slightly curved.
Vein
The middle coat is composed of a thick layer of connective tissue with elastic fibers, intermixed, in some veins, with a transverse layer of muscular tissue.
The white fibrous element is in considerable excess, and the elastic fibers are in much smaller proportion in the veins than in the arteries.
Additional images
File:Illu_artery.jpg, Artery wall
File:Illu vein.jpg, Vein
File:Gray450.png, Section of a medium-sized artery
File:Calcificatio atherosclerotica.jpg, Microphotography of arterial wall with calcified (violet colour) atherosclerotic plaque (haematoxillin & eosin stain)
References
External links
* - "Bird, vessels (LM, High)"
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Arteries