Classification of vessels in the cardiovascular system | Cardiovascular System

Classification of vessels in the cardiovascular system

The vessels are divided into the following structures: These structures continuously merge into each other. The information in brackets behind the terms will be explained in more detail later. General wall structure of blood vessels: In principle, the wall of arteries and veins consists of three layers: The outer layer, or connective tissue layer, contains nerves as well as some small blood vessels (Vasa vasorum) that supply the vessel itself.

The middle layer consists mainly of alternating proportions. Here there are smooth muscle cells, elastic fibers and collagen fibers.The inner layer consists of a single-layer, flat cell bond. In some arteries and veins a so-called Membrana elastica interna separates these two structures.

Exceptions to these common features are capillaries and venules. These only have a single-layer wall. The only differences between arteries and veins are the properties of the wall layers.

Arteries, for example, have a pronounced Membrana elastica interna in their inner layer (tunica intima), whereas veins do not. The middle layer (tunica media) is well developed in arteries. In veins this structure is rather weak.

The outer layer (tunica externa) of arteries is sparsely developed in contrast to veins. Arteries are divided into an elastic type and a muscular type. Arteries of the elastic type are usually strong arteries close to the heart, consisting mainly of elastic fibers.

These types of arteries are an important factor in a continuous blood flow. They achieve this through the so-called air vessel function. Arteries of the muscular type, on the other hand, are arteries far from the heart, which regulate the blood flow to the organs by changing the diameter of the vessels.

Arterioles

Arterioles are small arteries whose middle layer consists of a maximum of 2 layers of (smooth) muscle cells. They have an influence on vascular resistance, especially in regions far from the heart, and thus have an important influence on blood pressure. Capillaries

Capillaries have the smallest diameter of all blood vessels.

This lies with approx. 5-10 μm. This is of crucial importance, since the diameter of a red blood cell (erythrocyte) is approx.

7.5 μm and thus the lumen is just large enough for the erythrocytes to flow through. The capillaries run through the body like a net. They are thus able to ensure the supply of all body cells.

The capillary network is particularly pronounced in the lungs, kidneys and organs with hormonal function, as metabolic activity is particularly high here. The wall of the capillaries consists of a layer of flat endothelial cells, which line the inside of blood vessels. Venules

Venules, i.e. small veins, initially have about the same (wall) structure as capillaries.

Their diameter is 15-500 μm. As a result, a mass transfer is still possible in this section. This is why we also speak of post-capillary venules in this context.

The wall construction just mentioned, however, can change progressively. Collecting venules, for example, have the familiar wall construction with three layers. Venules and arterioles are the smallest blood vessels still visible to the eye.

Veins

As mentioned above in the classification of the vascular system, a distinction is made between small, medium and large veins. Large veins can reach a diameter of up to 10 mm. Their main task is to transport the blood back to the heart.

Arteries that lead the blood away from the heart usually run parallel to veins and have approximately the same circumference. The wall of the veins is each much more elastic and thinner. As a result, the inner radius of these vessels is also significantly larger.

The fact that veins have such a thin wall is also due to the fact that we speak of a low-pressure system. The physical pressure load in veins is much lower than in arteries. They also make it difficult to distinguish between the described structures of the tunica intima-, media- and externa in the venous system.

An additional special feature of veins are their valves. Venous valves are found in small and medium-sized veins. They are primarily responsible for ensuring the return of blood to the heart.

Venous valves themselves consist of a kind of “bulge” of the tunica intima, the innermost layer. Their function is similar to that of a valve. The valves open for blood flowing back to the heart.

Blood flowing away from the heart causes the valves to fill up, resulting in closure. Arterioles are small arteries whose middle layer consists of a maximum of 2 layers of (smooth) muscle cells. They influence vascular resistance, especially in regions far from the heart, and thus have an important influence on blood pressure.

Capillaries have the smallest diameter of all blood vessels. This is about 5-10 μm.This is of crucial importance, since the diameter of a red blood cell (erythrocyte) is about 7.5 μm and thus the lumen is just large enough for the erythrocytes to flow through. The capillaries run through the body like a net.

They are thus able to ensure the supply of all body cells. The capillary network is particularly pronounced in the lungs, kidneys and organs with hormonal function, as metabolic activity is particularly high here. The wall of the capillaries consists of a layer of flat endothelial cells, which line the inside of blood vessels.

Venules

Venules, i.e. small veins, initially have about the same (wall) structure as capillaries. Their diameter is 15-500 μm. As a result, a mass transfer is still possible in this section.

This is why we also speak of post-capillary venules in this context. The wall construction just mentioned, however, can change progressively. Collecting venules, for example, have the familiar wall construction with three layers.

Venules and arterioles are the smallest blood vessels still visible to the eye. Veins

As mentioned above in the classification of the vascular system, a distinction is made between small, medium and large veins. Large veins can reach a diameter of up to 10 mm.

Their main task is to transport the blood back to the heart. Arteries that lead the blood away from the heart usually run parallel to veins and have approximately the same circumference. The wall of the veins is each much more elastic and thinner.

As a result, the inner radius of these vessels is also significantly larger. The fact that veins have such a thin wall is also due to the fact that we speak of a low-pressure system. The physical pressure load in veins is much lower than in arteries.

They also make it difficult to distinguish between the described structures of the tunica intima-, media- and externa in the venous system. An additional special feature of veins are their valves. Venous valves are found in small and medium-sized veins.

They are primarily responsible for ensuring the return of blood to the heart. Venous valves themselves consist of a kind of “bulge” of the tunica intima, the innermost layer. Their function is similar to that of a valve.

The valves open for blood flowing back to the heart. Blood flowing away from the heart causes the valves to fill up, resulting in closure. Venules, i.e. small veins, initially have about the same (wall) structure as capillaries.

Their diameter is 15-500 μm. As a result, a mass transfer is still possible in this section. This is why we also speak of post-capillary venules in this context.

The wall construction just mentioned, however, can change progressively. Collecting venules, for example, have the familiar wall construction with three layers. Venules and arterioles are the smallest blood vessels still visible to the eye.

As mentioned above in the classification of the vascular system, a distinction is made between small, medium-sized and large veins. Large veins can reach a diameter of up to 10 mm. Their main task is to transport the blood back to the heart.

Arteries that lead the blood away from the heart usually run parallel to veins and have approximately the same circumference. The wall of the veins is each much more elastic and thinner. As a result, the inner radius of these vessels is also significantly larger.

The fact that veins have such a thin wall is also due to the fact that we speak of a low-pressure system. The physical pressure load in veins is much lower than in arteries. They also make it difficult to distinguish between the described structures of the tunica intima-, media- and externa in the venous system.

An additional special feature of veins are their valves. Venous valves are found in small and medium-sized veins. They are primarily responsible for ensuring the return of blood to the heart.

Venous valves themselves consist of a kind of “bulge” of the tunica intima, the innermost layer. Their function is similar to that of a valve. The valves open for blood flowing back to the heart.

Blood flowing away from the heart causes the valves to fill up, resulting in closure. Venous valves are found in small and medium-sized veins. They are primarily responsible for ensuring that blood flows back to the heart.

Venous valves themselves consist of a kind of “bulge” of the tunica intima, the innermost layer.Their function is similar to a valve. The valves open for blood flowing back to the heart. Blood flowing away from the heart causes the valves to fill up, resulting in closure.

  • Arteries (elastic type, muscular type)
  • Arterioles (small arteries)
  • Capillaries (vessels with the smallest diameter)
  • Venules (small veins)
  • Veins (small, medium and large veins; capacity vessels)
  • Tunica externa (outer layer)
  • Tunica media (middle layer)
  • Tunica intima (inner layer)