Ciorba: Technically, veins have muscles. The blood wouldn't be able to travel back to the heart well enough otherwise.
Wiki: The thick, outer-most layer of a vein is made of collagen, (Called 'Tunica Adventitia' or 'Externa') , wrapped in bands of smooth muscle (Called 'Tunica Media') while the interior is lined with endothelial cells (Called 'Tunica Intima').
Wiki: The thick, outer-most layer of a vein is made of collagen, (Called 'Tunica Adventitia' or 'Externa') , wrapped in bands of smooth muscle (Called 'Tunica Media') while the interior is lined with endothelial cells (Called 'Tunica Intima').
/biology
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