Because this shape works for the body. Somewhere in the evolution time line the creature which had the first cylindrical blood vessel survived and that information has been stored in the DNA and has past it on to its offspring.
The reason I believe it works is that it is the easiest shape to dilate or constrict.
Tagalog of cylindrical: mabilog
Bending a rectangular sheet into a cylindrical shape.
Yes, they're usually cylindrical in shape.
There are three major categories of veins: superficial veins, deep veins, and perforating veins. All varicose veins are superficial veins; they lie between the skin and a layer of fibrous connective tissue called fascia.
The cylindrical barrel floated down the stream.
There are three types of veins, superficial veins that are just beneath the surface of the skin, deep veins that are large blood vessels found deep inside muscles, and perforator veins that connect the superficial veins to the deep veins.
10 figure we make from cylindrical shape
Pulmonary veins
Non-cylindrical objects are objects that do not have a cylindrical shape. This includes objects with irregular shapes, such as spheres, cubes, pyramids, and cones among others.
Varicose veins are called dialated veins
Varicose veins.
Veins