Under Arterioles one understands the smallest of the visible arteries, which are represented in the entire vascular system of the body. Here they represent the transition from the arteries to the capillaries. They are not only there to connect the arteries to the capillaries, but also regulate the blood pressure and the flow rate of the blood through their width. The comparable venous blood vessels are therefore also referred to as venules.
The Arterioles are the finest arteries in the human vascular system that are still visible to the naked eye.On the one hand, they have the task of establishing a connection between the arteries and the capillaries.
On the other hand, due to their width (around 40 to 100 µm), they also regulate the speed of the blood and thus also the blood pressure. In an emergency, they can almost stop the blood flow. In the vascular system, they emerge from the surrounding arteries through an invisible transition.
The structure of the arterioles is basically the same as that of the arteries. However, the layers and walls of the finer blood vessels are less strong and less developed. Nevertheless, a distinction is made here between the two types of arteries: the intima, media and adventitia.
The fine ones are similar in structure Arterioles very much the stronger arteries into which these pass. With these, however, the vascular wall consists only of a very thin layer, which is composed almost predominantly of smooth muscle cells.
However, there are also fine network-like fibers (reticulin fibers) and a non-fenestrated, lumen-side endothelial lining which "encases" the arterioles. The inner membrane lining (membrana elastica interna), however, in contrast to the arteries, lies directly under the endothelial layer.
The outer membrane layer (membrana elastica externa), on the other hand, is completely absent, unlike the arteries. In terms of structure, the arterioles always flow into the capillaries in the direction of blood flow. The muscle cells and the inner membrane layer of the arterioles, and not those of the arteries, break down.
The Arterioles have the task of regulating the blood flow to the subsequent capillary vessel. Therefore, the diameter of the arterioles is controlled on the one hand by the nervous sympathetic nervous system and on the other hand by vasoactive hormones.
However, even very small hormonal or external fluctuations cause a change in resistance that should not be underestimated, whereby the arterioles have a great influence on blood pressure. This is also due to the fact that a strong branching in the individual arteriolar connections increases the frictional resistance of the blood, while it restricts the flow rate and lowers the blood pressure.
Of course, the opposite is true for less complex or wide arterioles. For this reason, arterioles are often referred to as resistance vessels. However, the arterioles also have an "intelligent" effect, for example by constricting in the event of greater blood loss and thus reducing the loss.
At the same time, the narrowing in the periphery leads to a centralization of the blood volume and ensures that vital organs can continue to be supplied with blood as well as possible. In an emergency, less important organs are cut off from the blood supply by narrowing the arterioles, or they are temporarily undersupplied.
As are the larger arteries too Arterioles particularly susceptible to vascular blockages and occlusions such as arteriosclerosis. Of course, the small size of the arterioles also plays a role here, which increases the risk.
This is because vascular blockages, which often occur with high cholesterol levels, are caused by fat cells that are transported in the arteries or wander around in them and ultimately stick to the vascular walls. If the passage is now too narrow - as can be the case with a transition from the artery to the capillaries - an occlusion can occur even without direct adhesion. Such an occlusion can have numerous serious consequences. It can cause an undersupply of the surrounding organs, strokes or a heart attack.
Another form of complaint is vascular narrowing, which can also have serious consequences in the arterioles. Mostly this is also caused by fat deposits on the fine walls of the arterioles. Blood clots (thrombi) represent further dangers, which can also lead to constrictions or occlusions. Corresponding narrowing of the arterioles can also be caused by malfunctions of the body, illnesses or old age.
It is therefore extremely important to consult a doctor at the first signs of narrowing or blockages in the blood vessels. Corresponding symptoms could include cold limbs, but also increased numbness or frequent tingling in certain parts of the body.