artery, artery, pulsating artery, vein, blood vessel, vessel English: artery
According to the microscopic building material predominant in the middle layer (tunica media) of the artery, two types of arteries can be distinguished Arteries of the elastic type are mainly the large arteries near the heart. These include the main artery (aorta) and the pulmonary arteries (arteriae pulmonalis) with their large outlets. All other subsequent arteries are of the muscular type. The transition between the two types is fluid and cannot always be precisely defined under the microscope (histologically).
Arteries of the muscular type (Arteriae myotypicae)
The group of arteries of the muscular type includes all arteries except the largest arteries (aorta and pulmonary arteries). These arteries are called this way because the middle layer (tunica media) contains mainly smooth muscles. Arterial vessels with only one muscle layer are called arterioles.
The innermost layer (intima, tunica intima) is called endothelium. This endothelium is a single-layer, gapless coating of flat cells. These cells are aligned parallel to the bloodstream and thus promote blood flow.
The individual cells in this layer are very closely connected (tight junctions, zonula occludens) and thus control the barrier between the interior of an artery and the surrounding area. The smooth surface of the innermost layer (endothelium) prevents components of the blood (white blood cells, platelets, red blood cells) from being deposited on the wall. Various proteins are released into the blood via the surface of the endothelium, which are supposed to counteract the formation of blood clots.
There is also a subendothelial layer at the transition from the inner to the middle layer. This layer changes with increasing age and is the decisive reason for arterial calcification (atherosclerotic vascular wall narrowing) in old age. The middle layer (media, tunica media) is the broadest layer of the arterial wall and consists almost exclusively of smooth muscle cells.
These muscle cells are arranged in flat spirals and connected to each other by tiny openings (gap junctions). The muscle cells of the media create (synthesize) a two-dimensional network of many elastic fibers, the so-called internal elastic membrane. Since this membrane is permeated by many small openings, it promotes the passage (diffusion) of various substances through the vessel wall.
The outermost layer of the artery (adventitia) consists of connective tissue that firmly anchors the artery to the surrounding tissue. The nerves and blood vessels (vasa vasorum) that supply the vascular wall are also located in the adventitia. The inner layers of the vascular wall are supplied directly by the blood flowing through the artery.
Arteries of the elastic type (Arteriae elastotypicae)
Arteries of the elastic type are mainly the arteries close to the heart such as the aorta and pulmonary arteries. The decisive difference to arteries of the muscular type is the structure of the middle layer (media). In arteries of the elastic type, there are only a few muscle cells that lie between a large layer of elastic lamellae.
Depending on how tight the muscle cells are, these arteries receive a different degree of pretension. The different structure of the middle layer (media) can therefore be explained by the fact that the arteries near the heart have a wind-vessel function. During the heartbeat, the blood is pumped out of the heart with great force and hits the vessel walls of the arteries near the heart with relatively great force. Since these vascular walls consist of many elastic lamellae, this strong blood ejection can be cushioned and thus the blood flow can be converted from a turbulent to a continuous flow. This movement of the vessel wall continues over all the arteries and is felt as a pressure pulse, for example on the wrist.