Venules
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A venole ( Latin Venula , German rarely also Venule ) is a small vein . Together with the arterioles, venules are the finest blood vessels that can still be seen with the naked eye . You can z. B. can be recognized by the sclera (white eye skin) of the eye as a fine vascular pattern ( episcleral vessels ).
Venules arise from the venous section of capillaries and unite with neighboring venules to form veins. Their basic structure is similar to that of veins, but they have no clear layer of smooth muscles ( tunica media ) and no venous valves . During leukocyte migration , during an immune response, the leukocytes flow into the lymph nodes via so-called high - endothelial venules .
Venules of different thicknesses differ somewhat in structure, so that a subdivision is made into postcapillary venules with a diameter of 10 to 30 micrometers , collecting venules (30-50 micrometers) and muscular venules (50-100 micrometers). The walls of the Sammelvenolen in addition pericytes single, branched smooth muscle cells. Only the muscular venules have a layer of overlapping, branched smooth muscle cells. The subsequent veins have two or more layers of smooth muscle cells.
Individual proof
- ^ Alfred Benninghoff , Detlev Drenckhahn : Anatomie. Cardiovascular system, lymphatic system, endocrine system, nervous system, sensory organs, skin . Ed .: Detlev Drenckhahn. 16th edition. tape 2 . Urban & Fischer, Munich 2004, ISBN 3-437-42350-9 , pp. 95 ( limited preview in Google Book search).