Blood vessels are elastic tubular formations of various diameters that make up a closed cardiovascular system ( Fig. 1 and 2 ) and perform the function of transporting blood to all organs and tissues, regulating their blood supply and participating in metabolism and gas exchange .
Blood vessels are divided into arteries, veins and capillaries. Arteries (see) carry blood from the heart to all tissues and organs, forming the arterial system; veins (see) draw blood from tissues and organs to the heart, forming the venous system. The capillaries are the thinnest blood vessels that connect the terminal branching of arteries (arterioles) with the onset of veins (venules) in the tissues; they close the bloodstream at the periphery. The capillary walls are devoid of the muscular layer and consist of a single layer of flat cells. Due to this wall structure, oxygen and carbon dioxide , as well as metabolic products, easily pass from the blood to the tissues and from the tissues to the blood. In some organs, the capillaries are located between the arteries, for example, in the glomeruli of the kidney , or between two veins, for example, in the lobules of the liver, and are called "wonderful" networks. In addition to the connections of the arterial and venous system through capillaries, there is also a direct connection between the smallest arteries and veins through the arteriovenous anastomoses, when the blood passes, bypassing the capillary bed.
In some anatomical formations (for example, in the cornea, lens, hyaline cartilage, epithelial tissue ), blood vessels are absent.
Allocate two closed systems of blood vessels (see. Circulation ). The vessels of the systemic circulation include the aorta (see) with arteries extending from it, the superior and inferior vena cava, the portal vein with the branches forming them;
The pulmonary trunk with its branches - the right and left pulmonary arteries and the same veins belongs to the pulmonary circulation system.
Along with the blood vessels in the human body there are lymphatic vessels that conduct lymph from the tissues into the venous bed. There are lymphatic capillaries, small lymphatic vessels inside the organs, lymphatic vessels on the surface of the organs, diverting the lymph from the organs, lymph trunks and ducts - the thoracic and the right lymphatic duct, flowing into the branches of the superior vena cava (see Lymphatic system ).
Blood vessels have pronounced age characteristics. Morphological changes are closely related to the growth of the body, with the structural and functional restructuring of organs and tissues at different age stages. Age-related changes relate to the diameter of blood vessels, wall thickness, their macro-, microscopic and histological structure.
In women, the saphenous veins have thinner walls, a smaller caliber, less distinctly protrude on the relief of the skin.
Blood supply of blood vessels occurs at the expense of own vessels. In some cases, it is due to the branches of the nearby arteries. The inner shell of blood vessels has not. From the capillary bed in the walls of the arteries are formed veins, which are usually among the two accompany the arterial sprig. In the walls of large blood vessels there are lymphatic capillaries and vessels.
The innervation of the blood vessels is carried out by vegetative and sensory somatic nerve fibers that approach the blood vessels in the composition of the branches of the mixed nerves. Impulses that come through the nerves that innervate the vessels cause either dilation or narrowing of the vessel lumen. Vegetative nerve fibers, ending with motor endings on the cells of the smooth muscles of the walls of blood vessels, perform vasomotor innervation - there is a reduction in the smooth muscles of blood vessels and their lumen is narrowed. Sensitive nerve fibers in all layers of the wall have a variety of sensitive endings - receptors . The presence of vasomotor and sensory nerve fibers in the blood vessel walls provides for vascular reflex reactions in response to various stimuli from the internal and external environment. In some large blood vessels there are areas with hypersensitivity, the so-called reflexogenic zones (the region of the carotid sinus, the mouth of the pulmonary and vena cava, portal vein, etc.).
Congenital arteriovenous aneurysms (see. Aneurysm ) occur as a result of impaired development of part of the capillary plexus and vessels of the embryo (developmental anomaly). As a result, arteriovenous fistula (single - large or multiple - small), through which arterial blood enters the veins, bypassing the capillaries, which leads to serious changes in blood circulation, are formed. The artery in the area of fistula expands, becomes coiled, its walls become thinner - “venisation” of the arteries. The wall of the veins, on the contrary, thickens, expanding its muscle and elastic fibers - the so-called arterialization of the veins.
Congenital arteriovenous aneurysms can be localized (on the finger) and widespread throughout the limb, occur in all areas and organs of the body; defeat is usually one-sided. Their course is characterized by repeated bleeding, sometimes fatal. Common symptoms include cardiac disturbance, discomfort in the heart area, palpitations , shortness of breath , an increase in the size of the heart, edema, congestive liver . All these changes occur as a result of the fact that the heart has to disperse an excessively large amount of blood, as part of the blood enters the venous system, bypassing the capillaries, through arteriovenous fistula. Local symptoms are varicose veins, their tension and pulsation, the absence of collapse of the veins when the limb is raised up. When auscultation of the aneurysm is determined by continuous sistolodiastolic noise. There is also a significant increase in the limb, an increase in skin temperature by 2-3 ° on the side of the lesion, violation of the trophism in the form of hyperhidrosis, ulceration and necrosis, discoloration of the skin with the formation of red-burgundy or brown spots. Treatment of congenital arteriovenous aneurysms is only surgical - ligation of the fistula and excision of the fistula connecting the artery and vein. With multiple fistula, all dilated vessels are excised along with arteriovenous anastomoses. Other anomalies of blood vessels are also subject to surgical treatment - aortic double arch, aortic coarctation (narrowing of the isthmus), arterial (Botallov) duct non-union, etc.
With traumatic injuries of soft tissues, injuries, traumatic amputations of limbs, primary and secondary bleeding occurs (see. Bleeding), pulsating hematomas and traumatic aneurysms. Terrible manifestations of vascular injury — bleeding, embolism (see), anemia of the brain, gangrene (see), etc. — necessitate the need for urgent active measures: 1) preliminary stop of bleeding; 2) operation on the vessel; 3) prevention of the consequences of blood loss; 4) prevention and treatment of shock (see); 5) prevention and treatment of local ischemic events associated with vascular injury; 6) prevention and treatment of wound infections (see. Wounds, injuries ); 7) functional treatment of the consequences of injury to the blood vessels, nerves, bones, soft tissues. Consistent and systematic carrying out of these measures is especially necessary in case of injuries of blood vessels. Imposing of a vascular suture (see) is possible only in the presence of the corresponding conditions (danger of an infection and bleeding). With prolonged clamping of blood vessels in the tissues there are deep irreversible changes.
During operations on the main vessels, accompanied by prolonged cessation of blood flow, there is a need to prevent ischemic complications.
Among all methods of preventing ischemic complications in these interventions, the method of vessel bypass is the most common. The principle of shunting is to create a workaround around the area of the vessel that is turned off from the blood circulation. Rubber, polyethylene or metal cannulas are used for this purpose.