As they transport blood against the force of gravity, veins require special mechanisms to ensure that blood doesn’t flow backwards.
Veins are part of the body’s extensive network of blood vessels, returning blood back to the heart to maintain a continuous circulation. And when things go wrong with them, you can end up with varicose veins.
The heart and blood vessels are known collectively as the circulatory system. With each heartbeat, oxygen-rich blood is pumped through arteries to all parts of the body. Tiny capillaries in body tissues allow the oxygen to be released, for use by cells.
Veins transport de-oxygenated blood back to the heart, ready to be pumped to the lungs to receive more oxygen. As they transport blood against the force of gravity, veins require special mechanisms to ensure that blood doesn’t flow backwards.
Deep and not so deep
There are two types of veins. Superficial veins are the ones you see as blue or purple vessels just under the skin. They have one-way valves to keep blood moving in the correct direction – towards the heart.
Deep veins lie between large muscles in the legs and arms. These veins don’t have valves and rely on the pumping action of the surrounding muscles to keep the blood moving. When you’re walking, for instance, muscle activity compresses the veins in your feet and legs.
These important mechanisms to assist blood flow through the veins are referred to as the “calf muscle pump” and the “foot pump”.
If the valves in the superficial veins don’t function efficiently, blood can flow backwards (this is known as venous reflux). This causes the pressure inside the vein to increase, leading to venous hypertension.
The thin walls of veins are not capable of withstanding much increase in pressure and they get pushed outwards. It’s these distended and visible veins that are known as varicose veins - “swollen, twisted, lengthened” veins.
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