The 9 types of blood vessels (and their functions and characteristics)

Blood is a vital connective tissue that circulates through different types of blood vessels to perform multiple functions essential to life: transport of waste, help in dementia against infections, thermoregulation of the body, transport of hormones , enzymes and also other regulating substances. , nutrient transport, etc.

In this article, we will talk about the different types of blood vessels that the human body that we can better understand its functions.

    What is the circulatory system?

    Before explaining the different types of blood vessels, it is advisable to give a few small brush strokes on the circulatory system, this being one of the most important devices available to the human body. Its most important functions are::

    • Transport hormones and also immune cells.
    • Transport waste.
    • Regulate and maintain fluid and electrolyte homeostasis.
    • Regulation and maintenance of body temperature homeostasis.
    • It plays an important role in human reproduction.

    What are the types of blood vessels?

    In the human body, there are basically 3 types of blood vessels: arteries, capillaries and veins.. And each of them has a different structure that characterizes it, there are also differences in the way blood flow circulates through each of these types.

      1. The arteries and their functions

      The first types of blood vessels we are going to talk about are the arteries that surround the body are made up of 3 layersalso called “tunics” and these, from the center outwards, are called: the inner robe, the middle robe and, finally, the adventitious or outer robe.

      Blood flowing through the arteries does so at high pressure, essentially there are pressure gradients (from higher pressure to lower pressure) and secondarily it is aided by the force of gravity.

      Before talking about the first types of blood vessels, which are the arteries, it is worth explaining its main functionsbeing those that we will enumerate next:

      • Transport blood from the heart to the small capillaries.
      • Maintain blood pressure and blood flow; essential for the blood to reach the arterioles and capillaries.
      • Dampen possible fluctuations in blood pressure and blood flow.
      • Properly regulate the distribution of blood that reaches each tissue according to its needs.

      Now that we know in general terms what the main functions of the arteries are, let’s see what the different types are. They can be classified according to their size and the characteristics of the average tunicthus differentiating elastic, muscular, small arteries and arterioles.

      1.1 The elastic arteries

      Elastic arteries they are the thickest that can be found in the body and they are those that come directly from the ventricles of the heartthe organ responsible for pumping blood at high pressure through these arteries, as well as the pulmonary artery and aorta.

      In addition, the elastic arteries are responsible for conducting blood to the pulmonary and systemic circuits of the body, so they have also been called “conductive arteries”. On the other hand, the branches that come out of the large arteries are also categorized as elastic arteries.

      It should be noted that these types of blood vessels are called elastic arteries because your middle tunic has an elastic component of great importance for good blood circulation.

        1.2 Muscular arteries

        The muscular arteries are intermediate in size between the small and the large arteries, and are called “muscular” because the average tunic they have has a lower percentage of elasticity than the previous ones and they also have a higher muscle component.

        It is important to note that in muscular arteries blood flows at a lower pressure than in large arteries (for example, elastic arteries).

          1.3 Small arteries and arterioles

          The arteries branch more and more into narrower vessels, until they end in tiny arterioles. the last small branches of the arterial system.

          On the other hand, the small arteries of the body have a diameter with great variability and are often distinguished from each other by the number of layers of smooth muscle. Besides, these small arteries could have up to 8 layers; while arterioles usually have 1 or 2 layers.

          The small arteries are responsible for regulating the blood flow to the capillaries and this is possible thanks to the contraction of their smooth muscles, which is why they are also called “resistance vessels”.

          It should be noted that at the ends or final parts of the arterioles there are very small vessels which form the metarterioles and where there are certain precapillary sphincters, these being responsible for lowering the blood pressure so that it can reach the capillaries.

            2. Capillaries

            Another type of blood vessel that we will discuss in this article is capillaries, which it is the blood vessels that have a smaller size and because of them the blood pressure is lower, it therefore circulates at a slower speed in order to allow an exchange of substances between the tissues and the blood. Moreover, the capillary wall is formed by a basal lamina and an endothelium.

            Next, we will look at the 3 types of existing capillaries: continuous capillaries, fenestrated and discontinuous capillaries.

            2.1 Continuous capillaries

            First, continuous capillaries they are those that are surrounded by a continuous endothelium, being in addition the least permeable and most abundant capillaries. These capillaries are found in the lungs, central nervous system (CNS), heart, skeletal muscles, connective tissue, etc.

            2.2 Fenestrated capillaries

            Capillaries generated they have endothelial cells that are perforated and are found in the endocrine glands and also in all the tissues of the body where there is a very intense exchange between different substances, such as the gall bladder, the kidneys or the intestinal mucosa.

            2.3 Discontinuous capillaries

            Discontinuous capillaries, also called “sinusoids”, it is these capillaries that have higher permeability because they leave larger spaces in the endothelial cells and, therefore, they are capillaries that are usually found in places in the body where there is a great exchange between substances, such as the liver, spleen or bone marrow.

              3. Veins

              The last of the groups of blood vessels we are going to talk about would be the veins, which they are the ones responsible for receiving the blood that comes from the capillaries and it is the veins that return the blood flow to the heart with the aim of restarting the whole circuit through which the blood passes so that the whole of the body and its organs can perform all their functions in the most efficient way possible.

              The blood that circulates in the veins does so at a lower speed and pressure than when it circulates in the arteries and, moreover, the veins have the same structure as the arteries, consisting of 3 coats.

              It should be noted that Veins have the ability to store a large amount of blood, so they have also been called “capacitive vessels”. On the other hand, these are also usually classified according to their size (from smallest to largest).

              3.1 Venules and small veins

              The smallest veins in the whole body, also called venulesThey are very small veins and in this category there are postcapillary venules responsible for receiving blood from the capillaries in order to direct this blood flow to the muscular venules. next to venules are the small veins.

              3.2 The middle veins

              The medium veins are those that are found in greater numbers in the body, being a type of veins that can reach a diameter of 10 millimeters. A large part of the middle veins, especially those of the lower limbs, they have a kind of valve in their inner robe which serves to prevent retrograde blood flow due to the force of gravity, otherwise the blood would not circulate properly in that part of the body and would accumulate in the same place.

              3.3 Large veins

              Finally, within these types of blood vessels, such as veins, we will speak of the large veins, which are responsible for receiving the blood flow from the other veins of the body in order to return it to the heart, at the level of the right needle connection to this organ.

              It should be noted that these veins have the largest diameter in the whole bodyfar exceeding 10 millimeters, reaching the midribs at most.

              Bibliographic references

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              • Lopez, A. & Macaya, C. (2009). Cardiovascular Health Book at Clínico San Carlos Hospital and BBVA Foundation. Bilbao: Editorial Nerea.
              • Martini, FH (2004). Atlas of Human Anatomy. Madrid: Pearson Education.
              • Roberts, A. (2020). The great book of the human body. Madrid: Editorial DK Spain.
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