Types of blood VESSELS and their function

Blood is a fundamental element for life de all living beings, since it constitutes the means by which hormones, nutrients or oxygen are transported between the different cells and tissues of the body. This liquid medium circulates through the interior of conduits called blood vessels, which have different characteristics. In this lesson from a Teacher we will explain what are the different types of blood vessels that make up the human body. If you want to know more, stay with us as we explain it to you below!

Index

1. What are the types of blood vessels?
2. Arteries and their function
3. Capillaries
4. Veins, another of the body's blood vessels

In the human body there are three types of blood vessels:

1. Arteries
2. Veins
3. Capillaries

Each of these blood vessels has its characteristic structure and differences in terms of blood conduction.

Another type of vessels closely related to blood circulation are the lymphatic vessels, which although they are not blood vessels themselves, are fundamental in the circulatory system.

The body arteries They are made up of three layers or tunics, which from the inside out are: the intima tunic, the middle tunic and the outer or adventitial tunic. Blood flows in the arteries under high pressure, mainly through pressure gradients (from higher to lower pressure) and secondarily aided by the force of gravity. According to their size and the characteristics of the middle tunic, they differ in:

Elastic arteries

These are the thickest arteries in the body and leave directly from the ventricles of the heart, which pumps blood at high pressure through them, such as the aorta and pulmonary artery. These arteries conduct blood to the systemic and pulmonary circuits of the body, which is why they are also known as conducting arteries. The branches that arise from the larger arteries are also classified as elastic arteries. They are called elastic because their middle tunic has a very important elastic component.

Muscular arteries

These arteries are intermediate in size between the largest and smallest arteries, so they are difficult to classify. They are known as muscular because their tunic media has a lower elastic component and a higher muscular component. In these muscular arteries, blood flows at a lower pressure than in larger ones.

Small arteries and arterioles

The diameter of the smallest arteries in the body is highly variable and they are usually distinguished from one another by the number of layers of smooth muscle. The arterioles usually have one or two layers, while the small arteries can have up to eight layers. These arteries regulate blood flow to the capillary networks by contracting their smooth muscles, which is why they are also known as resistance vessels.

At the end of the arterioles there are small vessels that form the metarterioles and that have some precapillary sphincters, responsible for further reducing the blood pressure of the blood entering the capillaries.

Capillaries are the types of blood vessels smaller in size. Through them the blood circulates at very low pressure and speed, to allow the exchange of substances between blood and tissues. Its wall is formed by an endothelium and a basal lamina. There are three types of capillaries:

Continuous capillaries

These are surrounded by a continuous endothelium. They are the most abundant and the least permeable, they are found in the central nervous system, lung, skeletal muscle, heart, connective tissue, etc.

Fenestrated capillaries

Its endothelial cells have perforations. They are found in the endocrine glands and in those tissues where the exchange of substances is very intense, such as the kidneys, the intestinal mucosa or the gallbladder.

Discontinuous capillaries

Also called sinusoids, they are the most permeable capillaries, as the endothelial cells leave large spaces in them. Because of this, these capillaries are common in sites of great exchange, such as the bone marrow, spleen, or liver.

Image: Valid without barriers

We finish this review of the different types of blood vessels by talking about the veins that receive blood from capillaries and return it to the heart to start the circuit again. In them, the blood circulates at a lower pressure and speed than in the arteries and they have the same structure of three tunics, although they are not well defined, and some valves. They store a large amount of blood, which is why they are often referred to as capacitance vessels. They are also classified by size.

Venules and small veins

They are very small veins. The postcapillary venules receive blood from the capillaries and direct them to muscle venules. Next, the small veins are placed.

Medium veins

Most of the veins are medium veins and can reach up to 10 mm in diameter. Many of them, especially the veins of the lower extremities, have valves in the tunica interna that prevent the retrograde flow of blood due to the action of gravity.

Large veins

Large veins are the largest in diameter in the body, much larger than 10 mm. They are where the blood comes from the other veins and the one that returns it to the heart at the level of the right atrium. These are the vena cavae.

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Ross MH et al, Histology. Text and color atlas with Cellular and Molecular Biology. 7th edition, Editorial Wolters Kluver