it is important for veins to have valves because of anastomosis.
it is important for veins to have valves because of anastomosis.
why is it important for veins to have valves?
anastomosis
vein









































veins are blood vessels that carry blood toward the heart. most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated blood to the heart. in contrast to veins, arteries carry blood away from the heart.









































veins are less muscular than arteries and are often closer to the skin. there are valves in most veins to prevent backflow.









































section::::structure.
vein
this process was later performed on the human body (in the image on the right): the physician tied a tight ligature onto the upper arm of a person. this would cut off blood flow from the arteries and the veins. when this was done, the arm below the ligature was cool and pale, while above the ligature it was warm and swollen. the ligature was loosened slightly, which allowed blood from the arteries to come into the arm, since arteries are deeper in the flesh than the veins. when this was done, the opposite effect was seen in the lower arm. it was now warm and swollen. the veins were also more visible, since now they were full of blood. harvey then noticed little bumps in the veins, which he realised were the valves of the veins discovered by his teacher, hieronymus fabricius. harvey tried to push blood in the vein down the arm, but to no avail. when he tried to push it up the arm, it moved quite easily. the same effect was seen in other veins of the body, except the veins in the neck. those veins were different from the others – they did not allow blood to flow up, but only down. this led harvey to believe that the veins allowed blood to flow to the heart, and the valves maintained the one way flow.
william harvey