Blood Vessels

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Tubular cavities for the transport of blood.

All blood vessels except the [capillary] have four layers.

The tunica interna (intima) is the innermost wall and consists of a continuous single row of endotheliumcells lying in the longitudinal direction of the vascular flow. It serves as a barrier to the tissue. The endothelium is separated from the wall by a basement membrane. It is a very smooth layer that ensures unimpeded blood flow. The second layer (Membrana elastica interna) is a thin layer of connective tissue (subendothelium). Here, Arteries has more elastic fibers. The tunica media (media) consists mainly of smooth muscles, in the veins thinner than in the large arteries, between which elastic material and collagenous fibrils lie. The collagen fibrils reduce the elasticity of the venous tube # The tunica externa (adventitia) has important functions in the supply and innervation of the blood and lymph vessel system. In addition, it forms a displacement bearing and a demarcation from neighbouring structures. Depending on the type of vessel, collagene and elastic fibres occur to varying degrees. It does not necessarily set itself off cleanly from its surroundings because its collagen fibres radiate into the surrounding tissue.

Die Wände der größeren Arterien müssen auch ernährt werden, daher sind in die äußere Wandung die Versorgung übernehmende kleine Arterien eingebaut, die aus der näheren Umgebung kommen. Venen und Lymphgefäße besitzen Klappen aus Intimataschen, die als Ausstülpungen in das Lumen ragen. Sie formen Ventile und richten den Blutstrom oder Lymphstrom zum Zentrum.

Ein eventueller Rückfluss (beispielsweise durch die Muskelpumpe) entfaltet die Klappen und verhindert diesen.

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