The tunica media (
New Latin "middle coat"), or media for short, is the middle
tunica (layer) of an
artery or
vein. It lies between the
tunica intima on the inside and the
tunica externa on the outside.
Artery
Tunica media is made up of
smooth muscle
Smooth muscle is an involuntary non-striated muscle, so-called because it has no sarcomeres and therefore no striations (''bands'' or ''stripes''). It is divided into two subgroups, single-unit and multiunit smooth muscle. Within single-unit mus ...
cells,
elastic tissue
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 ai ...
and
collagen
Collagen () is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whole ...
. It lies between the
tunica intima on the inside and the
tunica externa 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 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 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