Synonyms: Vas sanguineum, vein
Definition
A blood vessel is a hollow organ with a specific cell structure, which is characteristically composed of several wall layers. In the body, blood vessels form a coherent system for the transport of blood, the circulation of blood. They are responsible for the entire oxygen and nutrient transport in the body.
They form a complex system of strong arteries with thick wall layers down to small, fine capillaries. In the following, the subdivision and tasks of the blood vessels will be discussed in more detail. However, it should always be remembered that arteries always flow away from the heart and veins flow towards the heart.
The often known division into vessels with oxygen-rich or oxygen-poor blood is incorrect with regard to the large and small body circulation. The total length of all blood vessels in the human body can be up to 150 000 kilometres. It can also be said that blood flows in almost every part of our body.
Exceptions are the cornea of the eye (cornea), the enamel, hair and nails. Blood vessels can be subdivided again depending on their size and the blood to be transported. The largest vessels are the arteries.
They get smaller and smaller from arterioles to capillaries. Capillaries finally have the smallest diameter and only have a very thin wall structure. Therefore they are particularly suitable for gas exchange in the lungs.
The capillaries are then followed by the venules, which are responsible for the transport of blood low in oxygen. Vessels of this type with larger lumen are called veins. Separate from these are the aorta, the largest artery in the body, and the superior and inferior vena cava, which transports the collected blood back to the heart.
Furthermore, a distinction is made between a muscular and an elastic type of arteries. Arteries of the muscular type form the largest group. In contrast, the arteries close to the heart, such as the aorta and the large pulmonary vein, belong to the elastic type.
Function
The blood vessels and the heart as a pumping organ together form the blood circulation of the body. Via the blood circulation all organs, as well as the head, legs and arms are supplied with blood and the nutrients and oxygen dissolved in it. At the same time, decomposition products, metabolic waste products and carbon dioxide are transported away and returned to the lungs via the heart, where the blood is again enriched with oxygen.
The capillaries are the place for gas and material exchange. They are particularly well suited for this purpose, as they have a low layer thickness and a slow flow rate due to their thin diameter. Due to the slow blood flow in the capillaries, there is enough time to absorb oxygen from the inhaled air by diffusion and simultaneously release carbon dioxide.
