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What are vessels?
Vessels are tubular formations that extend throughout the human body and through which blood moves. The pressure in the circulatory system is very high because the system is closed. According to this system, the blood circulates quite quickly.
After many years, obstructions to the movement of blood – plaques – form on the vessels. These are formations on the inside of the vessels. Thus, the heart must pump blood more intensively in order to overcome the obstructions in the vessels, which disrupts the work of the heart. At this point, the heart can no longer deliver blood to the organs of the body and can not cope with the work. But at this stage it is still possible to recover. Vessels are cleared of salts and cholesterol deposits.
When the vessels are cleansed, their elasticity and flexibility return. Many diseases associated with blood vessels go away. These include sclerosis, headaches, a tendency to a heart attack, paralysis. Hearing and vision are restored, varicose veins are reduced. The state of the nasopharynx returns to normal.
human blood vessels
Blood circulates through the vessels that make up the systemic and pulmonary circulation.
All blood vessels are made up of three layers:
Inner layer endothelial cells form the vascular wall, the surface of the vessels inside is smooth, which facilitates the movement of blood through them.
Middle layer walls provides strength to blood vessels, consists of muscle fibers, elastin and collagen.
Upper layer Vascular walls are connective tissues, it separates the vessels from nearby tissues.
Arteries
The walls of the arteries are stronger and thicker than those of the veins, as the blood moves through them with greater pressure. Arteries carry oxygenated blood from the heart to the internal organs. In the dead, the arteries are empty, which is found at autopsy, so it was previously believed that the arteries are air tubes. This was reflected in the name: the word “artery” consists of two parts, translated from Latin, the first part “aer” means air, and “tereo” means to contain.
Depending on the structure of the walls, two groups of arteries are distinguished:
Elastic type of arteries – these are vessels located closer to the heart, these include the aorta and its large branches. The elastic framework of the arteries must be strong enough to withstand the pressure with which blood is ejected into the vessel from heart contractions. The fibers of elastin and collagen, which make up the frame of the middle wall of the vessel, help to resist mechanical stress and stretching.
Due to the elasticity and strength of the walls of the elastic arteries, blood continuously enters the vessels and its constant circulation is ensured to nourish organs and tissues, supplying them with oxygen. The left ventricle of the heart contracts and forcefully ejects a large volume of blood into the aorta, its walls stretch, containing the contents of the ventricle. After relaxation of the left ventricle, blood does not enter the aorta, the pressure is weakened, and blood from the aorta enters other arteries, into which it branches. The walls of the aorta regain their former shape, as the elastin-collagen framework provides them with elasticity and resistance to stretching. Blood moves continuously through the vessels, coming in small portions from the aorta after each heartbeat.
The elastic properties of the arteries also ensure the transmission of vibrations along the walls of the vessels – this is a property of any elastic system under mechanical influences, which is played by a cardiac impulse. The blood hits the elastic walls of the aorta, and they transmit vibrations along the walls of all the vessels of the body. Where the vessels come close to the skin, these vibrations can be felt as a weak pulsation. Based on this phenomenon, methods for measuring the pulse are based.
Muscular type arteries in the middle layer of the walls contain a large number of smooth muscle fibers. This is necessary to ensure blood circulation and the continuity of its movement through the vessels. Muscular-type vessels are located farther from the heart than elastic-type arteries, so the force of the cardiac impulse in them weakens, in order to ensure further movement of blood, it is necessary to contract the muscle fibers. When the smooth muscles of the inner layer of the arteries contract, they narrow, and when they relax, they expand. As a result, blood moves through the vessels at a constant speed and enters the organs and tissues in a timely manner, providing them with nutrition.
Another classification of arteries determines their location in relation to the organ whose blood supply they provide. Arteries that pass inside the organ, forming a branching network, are called intraorgan. Vessels located around the organ, before entering it, are called extraorganic. Lateral branches that originate from the same or different arterial trunks may reconnect or branch into capillaries. At the point of their connection, before branching into capillaries, these vessels are called anastomosis or fistula.
Arteries that do not anastomose with neighboring vascular trunks are called terminal. These include, for example, the arteries of the spleen. The arteries that form fistulas are called anastomosing, most of the arteries belong to this type. The terminal arteries have a greater risk of blockage by a thrombus and a high susceptibility to a heart attack, as a result of which part of the organ may die.
In the last branches, the arteries become very thin, such vessels are called arterioles, and the arterioles already pass directly into the capillaries. Arterioles contain muscle fibers that perform a contractile function and regulate the flow of blood into the capillaries. The layer of smooth muscle fibers in the walls of arterioles is very thin compared to the artery. The branching point of the arteriole into capillaries is called the precapillary, here the muscle fibers do not form a continuous layer, but are located diffusely. Another difference between a precapillary and an arteriole is the absence of a venule. The precapillary gives rise to numerous branches into the smallest vessels – capillaries.
Capillaries
Capillaries are the smallest vessels, the diameter of which varies from 5 to 10 microns, they are present in all tissues, being a continuation of the arteries. Capillaries provide tissue metabolism and nutrition, supplying all body structures with oxygen. In order to ensure the transfer of oxygen and nutrients from the blood to the tissues, the capillary wall is so thin that it consists of only one layer of endothelial cells. These cells are highly permeable, so through them the substances dissolved in the liquid enter the tissues, and the metabolic products return to the blood.
The number of working capillaries in different parts of the body varies – in large numbers they are concentrated in the working muscles, which need a constant blood supply. For example, in the myocardium (the muscular layer of the heart), up to two thousand open capillaries are found per square millimeter, and in skeletal muscles there are several hundred capillaries per square millimeter. Not all capillaries function at the same time – many of them are in reserve, in a closed state, to start working when necessary (for example, during stress or increased physical activity).
Capillaries anastomose and, branching out, make up a complex network, the main links of which are:
Arterioles – branch into precapillaries;
Precapillaries – transitional vessels between arterioles and capillaries proper;
True capillaries;
Postcapillaries;
Venules are places where capillaries pass into veins.
Each type of vessel that makes up this network has its own mechanism for the transfer of nutrients and metabolites between the blood they contain and nearby tissues. The musculature of larger arteries and arterioles is responsible for the promotion of blood and its entry into the smallest vessels. In addition, the regulation of blood flow is also carried out by the muscular sphincters of pre- and post-capillaries. The function of these vessels is mainly distributive, while true capillaries perform a trophic (nutritional) function.
Veins
Veins are another group of vessels, the function of which, unlike arteries, is not to deliver blood to tissues and organs, but to ensure its entry into the heart. To do this, the movement of blood through the veins occurs in the opposite direction – from tissues and organs to the heart muscle. Due to the difference in functions, the structure of the veins is somewhat different from the structure of the arteries. The factor of strong pressure that blood exerts on the walls of blood vessels is much less manifested in veins than in arteries, therefore the elastin-collagen framework in the walls of these vessels is weaker, and muscle fibers are also represented in a smaller amount. That is why veins that do not receive blood collapse.
Like arteries, veins branch widely to form networks. Many microscopic veins merge into single venous trunks that lead to the largest vessels that flow into the heart.
The movement of blood through the veins is possible due to the action of negative pressure on it in the chest cavity. Blood moves in the direction of the suction force into the heart and chest cavity, in addition, its timely outflow provides a smooth muscle layer in the walls of blood vessels. The movement of blood from the lower extremities upwards is difficult, therefore, in the vessels of the lower body, the muscles of the walls are more developed.
In order for the blood to move towards the heart, and not in the opposite direction, valves are located in the walls of the venous vessels, represented by a fold of the endothelium with a connective tissue layer. The free end of the valve freely directs blood towards the heart, and the outflow is blocked back.
Most veins run next to one or more arteries: small arteries usually have two veins, and larger ones have one. Veins that do not accompany any arteries occur in the connective tissue under the skin.
The walls of larger vessels are nourished by smaller arteries and veins that originate from the same trunk or from neighboring vascular trunks. The entire complex is located in the connective tissue layer surrounding the vessel. This structure is called the vascular sheath.
The venous and arterial walls are well innervated, contain a variety of receptors and effectors, well connected with the leading nerve centers, due to which automatic regulation of blood circulation is carried out. Thanks to the work of the reflexogenic sections of blood vessels, the nervous and humoral regulation of metabolism in tissues is ensured.
Functional groups of vessels
According to the functional load, the entire circulatory system is divided into six different groups of vessels. Thus, in the human anatomy, shock-absorbing, exchange, resistive, capacitive, shunting and sphincter vessels can be distinguished.
Cushioning Vessels
This group mainly includes arteries in which a layer of elastin and collagen fibers is well represented. It includes the largest vessels – the aorta and the pulmonary artery, as well as the areas adjacent to these arteries. The elasticity and resilience of their walls provides the necessary shock-absorbing properties, due to which the systolic waves that occur during heart contractions are smoothed out.
The cushioning effect in question is also called the Windkessel effect, which in German means “compression chamber effect”.
To demonstrate this effect, the following experiment is used. To the container, which is filled with water, two tubes are attached, one of an elastic material (rubber) and the other of glass. From a hard glass tube, water splashes out in sharp intermittent shocks, and from a soft rubber one it flows evenly and constantly. This effect is explained by the physical properties of the tube materials. The walls of an elastic tube are stretched under the action of fluid pressure, which leads to the emergence of the so-called elastic stress energy. Thus, the kinetic energy that appears due to pressure is converted into potential energy, which increases the voltage.
The kinetic energy of cardiac contraction acts on the walls of the aorta and large vessels that depart from it, causing them to stretch. These vessels form a compression chamber: the blood entering them under the pressure of the systole of the heart stretches their walls, the kinetic energy is converted into the energy of elastic tension, which contributes to the uniform movement of blood through the vessels during the diastole.
The arteries located farther from the heart are of the muscular type, their elastic layer is less pronounced, they have more muscle fibers. The transition from one type of vessel to another occurs gradually. Further blood flow is provided by the contraction of the smooth muscles of the muscular arteries. At the same time, the smooth muscle layer of large elastic type arteries practically does not affect the diameter of the vessel, which ensures the stability of hydrodynamic properties.
Resistive vessels
Resistive properties are found in arterioles and terminal arteries. The same properties, but to a lesser extent, are characteristic of venules and capillaries. The resistance of the vessels depends on their cross-sectional area, and the terminal arteries have a well-developed muscle layer that regulates the lumen of the vessels. Vessels with a small lumen and thick, strong walls provide mechanical resistance to blood flow. Developed smooth muscles of resistive vessels provide regulation of blood volume velocity, control blood supply to organs and systems due to cardiac output.
Vessels-sphincters
Sphincters are located in the terminal sections of the precapillaries; when they narrow or expand, the number of working capillaries that provide tissue trophism changes. With the expansion of the sphincter, the capillary goes into a functioning state, in non-working capillaries, the sphincters are narrowed.
exchange vessels
Capillaries are vessels that perform an exchange function, carry out diffusion, filtration and trophism of tissues. Capillaries cannot independently regulate their diameter, changes in the lumen of the vessels occur in response to changes in the sphincters of the precapillaries. The processes of diffusion and filtration occur not only in capillaries, but also in venules, so this group of vessels also belongs to the exchange ones.
capacitive vessels
Vessels that act as reservoirs for large volumes of blood. Most often, capacitive vessels include veins – the peculiarities of their structure allow them to hold more than 1000 ml of blood and throw it out as needed, ensuring the stability of blood circulation, uniform blood flow and full blood supply to organs and tissues.
In humans, unlike most other warm-blooded animals, there are no special reservoirs for depositing blood, from which it could be ejected as needed (in dogs, for example, this function is performed by the spleen). Veins can accumulate blood to regulate the redistribution of its volumes throughout the body, which is facilitated by their shape. Flattened veins contain large volumes of blood, while not stretching, but acquiring an oval lumen shape.
Capacitive vessels include large veins in the womb, veins in the subpapillary plexus of the skin, and liver veins. The function of depositing large volumes of blood can also be performed by the pulmonary veins.
Shunt vessels
Shunt vessels are an anastomosis of arteries and veins, when they are open, blood circulation in the capillaries is significantly reduced. Shunt vessels are divided into several groups according to their function and structural features:
Heartfelt blood vessels – these include elastic type arteries, vena cava, pulmonary arterial trunk and pulmonary vein. They begin and end with a large and small circle of blood circulation.
Main vessels – large and medium-sized vessels, veins and arteries of the muscular type, located outside the organs. With their help, blood is distributed to all parts of the body.
Organ vessels – intraorgan arteries, veins, capillaries that provide trophism to the tissues of internal organs.
Diseases of the blood vessels
The most dangerous vascular diseaseslife-threatening: aneurysm of the abdominal and thoracic aorta, arterial hypertension, ischemic disease, stroke, renal vascular disease, atherosclerosis of the carotid arteries.
Diseases of the vessels of the legs – a group of diseases that lead to impaired blood circulation through the vessels, pathologies of the valves of the veins, impaired blood clotting.
Atherosclerosis of the lower extremities – the pathological process affects large and medium-sized vessels (aorta, iliac, popliteal, femoral arteries), causing their narrowing. As a result, the blood supply to the limbs is disturbed, severe pain appears, and the patient’s performance is impaired.
Phlebeurysm – a disease that results in the expansion and lengthening of the veins of the upper and lower extremities, the thinning of their walls, the formation of varicose veins. The changes that occur in this case in the vessels are usually persistent and irreversible. Varicose veins are more common in women – in 30% of women over 40 and only 10% of men of the same age. (Read also: Varicose veins – causes, symptoms and complications)
Which doctor should I contact with vessels?
Vascular diseases, their conservative and surgical treatment and prevention are dealt with by phlebologists and angiosurgeons.
After all the necessary diagnostic procedures, the doctor draws up a course of treatment, which combines conservative methods and surgery. Drug therapy of vascular diseases is aimed at improving blood rheology, lipid metabolism in order to prevent atherosclerosis and other vascular diseases caused by elevated blood cholesterol levels. (See also: High blood cholesterol – what does it mean? What are the causes?) The doctor may prescribe vasodilators, medicines to combat associated diseases, such as hypertension. In addition, the patient is prescribed vitamin and mineral complexes, antioxidants.
The course of treatment may include physiotherapy procedures – barotherapy of the lower extremities, magnetic and ozone therapy.