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Blood vessel

Synonym: Vas sanguineum

1 Definition

A blood vessel is a hollow organ that is responsible for the transport of blood throughout the body. It is formed by pipe shaped tissue that is made up of at least one, and often multiple wall layers. These layers form a hollow body and enclose the so called vascular lumen.

2 Task

In total the blood vessels form the anatomical basis of the circulatory system and with that also for the oxygen and nutrient supply of the body. Through them blood is transported from the heart to the periphery and back.

3 Classification

Blood vessels can be classified as:

Occasionally the aorta and vena cava are mentioned separately due to their special anatomical structures.

4 Anatomy

In general, the walls of major blood vessels consist of the following three structures:

Capillaries are built in a simpler way. They are solely made up of a thin endothelium which is covered by vastly branched pericytes. Contrary to other blood vessels they are permeable, meaning that certain molecules and cells can pass through their walls.

4.1 Intima

The intima is made up of a single layer of endothelial cells, oriented along the longitudinal axis of the vessel. It plays a significant role in the exchange of gas, liquids, and other substances between blood and the surrounding tissue.

4.2 Media

The media is made up of a layer of smooth muscle and/or elastic connective tissue. Its thickness varies depending on the type of vessel. For example one can differentiate between elastic arteries close to the heart (Windkessel effect) and the more distal distributing arteries (muscular arteries).

4.3 Adventitia

The adventitia is the tissue surrounding the outside of the vessel. It can include small vessels (vasa vasorum) for the nourishment of vessels with thick walls.

5 Physiology

Blood vessels can adjust their diameter by contracting their muscular layer. This enables the vessel to regulate the blood flow. This is especially true for vessels with a thick muscular layer, such as arteries, and with some limitations also applies to veins. The regulation of the vessel diameter is achieved through fibers of the autonomic nervous system. Two antagonistic reactions can be provoked:

Through the help of this simple mechanism, the body is able to govern the distribution of its available blood volume. It can for example help to improve the oxygen supply, or thermal regulation of individual body areas. Within the blood vessels the physiological blood pressure ranges in the arterial system from about 80-120 mm Hg and has a maximum of 10 mm Hg in the venous system (central venous pressure).

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