Arterioles
Arterioles are small arteries that are found in the bloodstream in front of the arterial capillaries and behind the arteries. The venous equivalent to this are the so-called venules. Venules and arterioles are the finest blood vessels that are still visible to the naked eye .
Definition
Arterioles (singular arteriola) are visible arteries that occur throughout the vascular system. They have a diameter of around 20 microns, connect the arteries with the capillaries and regulate blood pressure and blood flow.
Anatomy
The walls of the arterioles basically have the same structure as those of the arteries, whereby a distinction can be made between tunica interna, tunica media and tunica externa. However, the layers and walls of the arterioles are not as strong and consist mostly of smooth muscle cells.
In addition, fine fibers (called reticulin fibers) and an endothelial lining are also present. Endothelial cells are very flat cells that line the inner walls of blood vessels . They form the so-called endothelium, a single-layered squamous epithelium.
The inner membrane lining (membrana elastica interna) is located directly under the endothelial layer. The media can completely close the arterioles so that the blood does not flow uncontrolled into the capillary bed and organs that are less stressed also have less blood flow.
The media of larger arterioles consists of two muscular layers, but many arterioles have only one closed muscular layer. In addition, there are numerous caveolae in the plasma membrane of the endothelial cells, which enlarge the cell surface. In the direction of blood flow, the arterioles then merge into the capillaries.
Function
The arterioles regulate the blood flow in the capillaries. For this reason, the diameter of the arterioles is controlled by vasoactive hormones or the nervous sympathetic nervous system. Even a small hormonal fluctuation leads to a large change in resistance, which affects blood pressure.
If the arterioles are highly branched, the frictional resistance of the blood increases and the blood pressure drops. Exactly the opposite occurs with dilated arterioles. Therefore, arterioles are also referred to as resistance vessels. In addition, they narrow when there is a large loss of blood and can therefore reduce it.
The narrowing centralizes the blood volume so that the organs continue to be adequately supplied with blood. In an emergency, organs that are less important are undersupplied or cut off from the blood supply.
Diseases
Arterioles, like larger arteries, are prone to occlusion or vascular blockage, which is referred to as arteriosclerosis. Due to the small diameter of the arterioles, there is an increased risk of this.
Vascular blockages occur, for example, as a result of increased cholesterol levels. Then fat cells are transported in the arteries and stick to the walls of the vessels. If the passage is too narrow, an occlusion occurs, which can lead to serious consequences. The surrounding organs are undersupplied and a heart attack or stroke can occur.
Another condition is vasoconstriction caused by fatty deposits. Blood clots (thrombi), which can also lead to an occlusion or narrowing, are also dangerous.
However, vasoconstriction can also be caused by age, various diseases or physical malfunctions. A doctor should therefore be consulted immediately at the first sign of a vascular blockage. Symptoms of vasoconstriction include, for example, increased numbness , tingling or cold limbs.
Arteriosclerosis usually begins at a young age. In addition, people who are overweight or smoke can develop vasoconstriction more quickly. If arteriosclerosis is detected in time, it is possible to reverse the damage by changing your diet.
Fatty food and alcohol should be avoided, and plenty of exercise and sport is also important. In the case of very severe arteriosclerosis, the vessels may have to be widened, so-called stents are then used for support to prevent repeated narrowing.
In addition , inflammation of the arterioles can occur due to vasculitis , with type 3 allergy very often being responsible for this. Vasculitis causes the vessels to stretch and form bulges, which can cause life-threatening bleeding ( aneurysms ).
Sometimes there is also swelling in the inner lining of the vessel, which can lead to complete occlusion. If the smallest vessels are affected, increased permeability of the wall must be expected, which means that blood components or blood can escape into the surrounding tissue. If the vessel wall is destroyed, the tissue that is supplied by the blood vessel can no longer be supplied with blood and an infarction is the result.
Depending on which organs are involved, different symptoms occur. These include, for example, rheumatic complaints, red eyes , cardiac arrhythmia , fatigue , night sweats or concentration problems.
Hello and welcome to my Health Guide & Encyclopedia! My name is Dorothy Farrar, and I'm the founder and main author of this platform.
My passion for health and wellness started at a young age when I became interested in the connection between the food we eat and the way we feel. This fascination led me to study nutrition and dietetics in college, where I learned about the importance of a balanced diet and the impact of various nutrients on the body.