How Veins Work

The Circulatory System

The circulatory system is responsible for delivering oxygen to cells. It is made up of the heart, arteries, veins, capillaries, and blood. The heart’s pumping action forces oxygenated blood from the heart and lungs to millions of cells throughout the body via arteries and capillaries. After the blood has been through the tissues, delivering oxygen and food to keep the cells alive, it collects together in the veins.
Blood then returns to the heart through the Veins.
The heart pumps the blood through the arteries at high pressure, and so it moves quickly down the leg and into the tissues.
However getting blood back from the legs isn't so easy. There is no "heart" in the leg and so the body needs a different way to get blood back to the heart.

The Circulatory System

Standing Up

When you stand up, the heart is raised above the feet. This increases the pressure in the blood because of the weight of the column of blood from the heart to feet. This is called "Gravitational" or "Hydrostatic" pressure.
This extra pressure from standing helps the blood to flow from the heart to the legs, in the arteries. But, this same "Gravitational" or "Hydrostatic" pressure means that there is NOT enough pressure in the blood in the veins to get back to the heart.
This is the reason that that people who have to stand still (such as soldiers on parade) faint. They cannot get the blood out of their legs and so they cannot get it pumped to their brains, and so they faint.
So, to stop this happening, blood needs to be pumped out of the legs and get back to the heart.

Standing Up

Function of Leg Pump or Muscle Pump or "Peripheral Heart"

The fact that we do not usually faint when we sit up or stand up shows that the blood does usually get back to the heart. With the gravitational pressure pushing down on the blood in the leg, there needs to be a pump that pushes the blood back from the ankle and lower leg into the pelvis from where it can be helped back to the heart by breathing. The Peripheral Heart is a system of muscles, veins, and valves in the calf and foot that work together to push deoxygenated blood back up to the heart and lungs. Veins are equipped with one-way valves that prevent backflow during the return of blood from the toes to the heart. These valves act as trap doors that open with each muscle contraction and close when the muscle relaxes in order to prevent the backflow of blood.
The Leg Pump depends on two factors to pump the blood back up from the foot and into the pelvis:

Function of Leg Pump

Movement

The movement of the muscles in the leg push on the veins and squash them. The most important of these movements is the calf muscle moving the ankle joint.
The picture on the right shows the calf muscle moving the ankle joint - watch how it squashes the vein within it when the muscle contracts

Movement

Valves - situated in the veins

Pressure from the muscles squashing the veins will make the blood move. But without valves the blood moves without direction and so the blood is not pumped out of the leg. The prevention of this reflux by the valves is the key to how veins protect the legs in normal people. When the valves are working the vein is said to be "competent”. When valves become defective or weak they cannot function properly. In turn, the second heart becomes overwhelmed and blood is allowed to pool in the veins.

The picture on the right shows what would happen if there were no valves at all in veins but the muscle contracted as normal.
There are 2 systems of veins at work in the legs: the Deep system and the Superficial system. The deep system contains the big veins that are approximately 1 inch in diameter and are situated close to the bone, surrounded by muscle. The superficial system contains the veins that are visible directly under the surface of the skin. The systems meet at 2 junctions and through a series of connecting veins called perforators 90% of the Venous blood of the Legs is returned back to the heart by the Deep Venous System, and 10% by the Superficial Venous System.

Valves - situated in the veins

The Superficial System consists of two main systems

The Great Saphenous Vein: This starts around the inner side of the ankle, and goes upwards to the groin, where it joins the Deep Veins. At this point,there is a major one way venous valve, called the Sapheno Femoral valve. If this valve starts leaking, then the blood accumulates in the great Saphenous vein, causing dilatation along its length.

The Short Saphenous System: This superficial vein of the leg starts around the outer side of the ankle, and goes upwards to behind the knee, where it enters the Deep Veins. At this point, there is a venous valve called the Sapheno Popliteal valve. Leakage of this valve leads to dilatation of the Short Saphenous vein.

Perforator Vein Valves

At various levels in the legs, there are small communicating veins between the Superficial veins and the Deep Veins. These are called perforator veins and they have a perforator valve, which enables flow of blood from the superficial to the deep system. If this valves leak, then the blood flows directly from the deep to the superficial veins. This is most commonly responsible for the pigmentation that is seen around the ankles in patients with varicose veins. Seen these veins are perpendicular to the skin, do dilated veins are visible.

Perforator Vein Valves

The Leg Pump - Failing due to Abnormal Valves

When the valves in a vein do not work, they are called "incompetent". The muscle squeezes the vein and the blood is forced up and out of the vein, as in normal veins. However, when the pressure eases and the veins open up, the blood is allowed to fall back down the leg as the valves are not able to prevent it. This is called venous "reflux". Virtually every problem associated with venous disease ie: varicose veins, leg aching, venous eczema, lipodermatosclerosis and venous leg ulcers, are caused by a FAILURE OF THE LEG PUMP and subsequent Venous reflux.

Functioning Valves in Veins

Leg Pump with No Valves

Failing Valves

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