Overview arterioles (Arteriolae):
Pages with explanations are linked to the
text below the images if available! (Labelling is in German)
Arteriols (small pulse vessels; Terminologia histologica: Arteriolae) are
vessels transporting blood away from the heart.
They are not as large as arteries which
they connect via metarteriols to capillaries. Metarteriols
are the smallest arteriols that only show a single layer of smooth
muscle cells. While loosing these smooth
muscle cells and the internal elastic membrane they finally become
|metarteriole + blood cells
|metarteriole + plasma cells
in connective tissue (monkey)
|elastica interna of an
|longitudinal section of
a wall of an arteriole (rat)
|wall of a larger
Regarded from interior to exterior the wall of an arteriole
has the following layers:
1. Tunica intima consists of an endothelium
and an internal elastic membrane.
The endothelium has a monolayer of squamous endothelial
cells. The squamous character of the endothelial cells can only be
seen under the high pressure physiologically present in living individuals.
Since preparations are usually NOT fixed and embedded under pressure endothelial
cells artificially appear cuboid or even columnar in most preparations.
In contrast to arteries that have a Stratum
subendotheliale the latter is lacking in arteriols. This means
the endothelial cells directly contact the
internal elastic membrane.
The internal elastic membrane (Membrana
elastica interna) is a thick membrane consisting of elastic fibres.
It comprises the border to the media.
2. Tunica media The media mainly shows smooth
muscle cells and some elastic- and collagen
3. Tunica externa (adventitia) The adventitia is a smooth
connective tissue rich in collagen
fibres with fibrocytes and free
connective tissue cells. It is fixing the arteriole to surrounding
tissues and shows some non-myelinated nerve
fibres. In contrast to arteries,
no nutrifying own vessels (Vasa vasorum) and no external
elastic membrane is seen in arteriols.
--> Arteries, blood
vessels, endothelial cells
--> Electron microscopic atlas Overview
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Three images were kindly provided by Prof. H. Wartenberg;
other images, page & copyright H. Jastrow