The vein

Veins (Latin singular vena, in subject-specific linguistic compositions phlebo- from the Greek genitive singular “φλέβας”, “phlébas”, in ancient Greek “φλέψ” phleps, “artery”) or in German veins are blood vessels transporting the blood to the heart. They transport approx. 7,000 liters of blood to the heart per day in an adult. Especially the leg veins have to work hard as the blood has to be transported in the opposite direction of the gravity of the heart.

Vein functioning

The systemic circulation veins transport oxygen-deficient blood, and the pulmonary circulation veins transport oxygen-rich blood. Oxygen-deficient blood is darker than oxygen-rich blood. The blood pressure in veins is clearly lower than in the arteries; they belong to the capillary, and the venule belongs to the low pressure system of the blood circulation.

Relationship to arteries

Approx. 90% of blood can be found in the veins. Most systemic veins are accompanying veins, i.e. they are parallel to the arterial equivalent.

Importance of musculature for blood flow

The foot and leg muscles naturally pump blood within veins. Always during the muscle tension, the blood is pressed against gravity upwards towards the heart. Dozens of venous valves are like non-return valves that are responsible for the blood not flowing back downwards during the relaxation of the muscle. Therefore, the use of the foot and leg muscles is very important for healthy veins. Climbing stairs, walking, hiking, riding a bike, or swimming keep the muscle pump active and increase the blood flow.

Vein manifestation

The blue manifestation of cutaneous veins depends not only on the oxygen content of the venous blood. Cutaneous veins seem to be blue in particular because the long-wave red light has a higher degree of penetration into tissue than blue, and for this reason, it is absorbed from the dark blood of the veins. Otherwise, the short-wave blue light is reflected; the veins seem to be blue at a tissue depth of 0.5 to 2 millimeters.

Vein structure

Veins reveal a typical three-layer appearance of the wall in the tunica interna (intima), tunica media (media), and tunica adventitia (A) that is comparable to all other blood vessels.

Importance of the venous valves

In case of arteries, the pump pressure of the heart is sufficient to avoid reflux. However, in the veins, the pump pressure of the heart is significantly decreased. In contrast to arteries, veins are fitted with a venous valve. Venous valves are pocket-like cusps of the venous intima. They occur in almost all veins at regular intervals. The venous valves have an important function: They control the blood flow toward the heart. They open in the direction of the blood flow. They close in case of reflux. Therefore, it is only possible for the blood flow to move in one direction. The venous valves are very important within the leg as gravity is contrary to venous flow. In case of functional disorders of the venous valves, valvular closure is insufficient. The blood can only flow back into the leg by increasing the pressure and gravity. In many cases, the orifice valve V. saphena magna is affected by an insufficiency of the valves. There are no venous valves in the veins of the head, bowels, vertebral canal, and large vessels close to the heart.