A blood vessel is a tubular structure used to transport blood. The vessel is also called a vein and is found only in the human and animal body.
What are blood vessels?
The totality of blood vessels, together with the heart, forms the circulatory system. This is essential for the circulation of blood to supply parts of the body. The blood vessels themselves are divided into different categories depending on their shape and function. Among the most important is the aorta as the main artery. In addition, there are the arteries. Their function is to carry blood away from the heart. In contrast, veins carry blood toward the heart. Finally, capillaries play an important role. As so-called hair vessels, they form the branching of the arteries. A blood vessel consists of tissue surrounded by at least one wall layer. Thus, the vein functions as a hollow organ and is responsible for the loss-free transport of blood. The transport network, with all its branches, reaches a length of up to 150,000 kilometers. 75 percent of the blood runs in the veins, another 20 percent in the arteries and only five percent in the capillaries.
Anatomy and structure
A blood vessel can be divided into three layers: the intima, the media, and the adventitia. The former layer is the innermost layer of the vessel wall. In science it is called tunica interna. Characteristic of the intima is that it consists of only a single layer of vascular cells. The cells are arranged in such a way that the best possible exchange of gases and fluids between blood and vein is possible. Specifically, the intima consists of a basement membrane. This is a layer of connective tissue cells that are aligned along a vessel. In contrast, the media is a muscular layer that is surrounded on both sides by connective tissue. In addition, there is the adventitia consisting of a loose connective tissue. Its purpose is to embed the blood vessel within the body. It should be noted that capillaries are sheathed only from a single layer. It is composed of vascular cells and resembles the intima in shape and expression.
Function and tasks
In the human body, blood vessels branch out to almost all parts of the body. In addition to transporting blood, their function is to constantly supply the body with nutrients. Here, the vascular diameter of the veins plays an important role. Depending on the width, the blood flow and the associated supply of nutrients varies. To control the vascular diameter, blood vessels can change in size. This is accomplished with the contraction of the muscle layer. The intensity of the contraction is in turn regulated by the body’s autonomic nervous system. With vasodilatation and vasoconstriction, the nervous system also manages to regulate the oxygen supply. In addition, the core temperature within the internal organs is controlled. Depending on the type, veins perform a specific task. The aorta, for example, fulfills the so-called Windkessel function. This is a mechanism responsible for equalizing the pressure of the blood expelled from the heart. So-called baroreceptors measure the pressure of the blood so that the aorta can react to a change by dilating or constricting the blood vessels. The vena cavae also play an important role. These are two comparatively large veins that transport venous blood to the right atrium of the heart. Venules play a special role. They are a scaled-down version of the veins that provide a profound branching of the transport network.
Diseases and disorders
The circulatory system is a vulnerable system. In many cases, a malfunction of the blood vessels is the cause of a complaint. One of the best-known conditions is arteriosclerosis. Colloquially, it is referred to as hardening of the arteries. The disease causes the veins to thicken and harden. As a consequence, the vessels narrow, which impedes blood flow to the respective region of the body. The cause of arteriosclerosis is a genetic predisposition. However, risk factors such as smoking or weight gain can promote the onset of the disease. In addition, hemorrhoids are a common disease of the blood circulation. This is referred to as a nodular dilatation of the arteries within the rectum.Dilatation of the blood vessels can be attributed to increasing connective tissue weakness. Patients experience pain and persistent itching in the affected area. If left untreated, inflammation and eczema may occur, accompanied by the discharge of a mucous secretion. Hemorrhoids can be relieved by the application of ointments and suppositories. However, in the long term, it is important to change lifestyle habits. Otherwise, a new outbreak may occur. On the other hand, a thrombosis, also known as a blood clot, leads to a particularly severe disturbance of the blood circulation. Here, an occlusion of a single blood vessel takes place. This results in obstruction of the blood flow and is accompanied by a reduced oxygen supply. In severe cases, thrombosis can cause pulmonary embolism and be fatal. Finally, another disease of the blood vessels is varicosis, colloquially known as varicose veins. This is a thickening of veins in the legs. The cause can be a weakness of the connective tissue. Varicosis is noticeable by a feeling of tension and heaviness. In addition, there is itching of the skin, which increases in intensity as the disease progresses.
