The return of venous blood from the legs back to the heart is accomplished
by numerous valves which are located in the veins, and the leg's "muscle
pump." Normal veins contain one-way valves that permit the blood to flow
from the periphery back toward the heart. These valves are necessary because
of our upright posture, and the effect of gravity, which would otherwise
cause the blood to pool in our feet and legs every time we stand. The
"muscle pump" is made up of muscle groups in the calf. When these muscles
contract, blood is forced upward toward the heart, through the one-way
valves. The blood cannot flow "backwards" toward the feet, because of
the presence of the valves. When the muscles relax, the valves prevent
the blood from flowing back down to the feet. The empty veins in the feet
and legs can now accept new blood coming from the feet, and the process repeats.
Large varicose veins are formed when the valves in the legs malfunction.
The valves become "incompetent," and begin to leak. As a result, blood
can leak back down to the feet and legs, because of the action of gravity.
This causes the veins to become distended, which causes further valves
to leak because of the increase in size of the vein channel. Over time,
these veins become large, "ropy," and visible to the naked eye. The word
"varicose" comes from the Greek word for "cluster of grapes," which these
veins can come to resemble. Varicose veins can cause discomfort, and typical
symptoms include pain, burning, heaviness, or tingling.
Superficial, small blue or red-blue spider veins, also called telangiectasais,
are a result of reflux into tiny venules in or just below the skin. Reticular
veins, also called feeder veins, often supply such telangiectasias. Spider
veins may cause symptoms of pain--especially pain which is aggravated
by prolonged periods of standing--as well as itching or tingling sensations.