Since the discovery by the British physician W. Harvey of the law of blood movement through vessels by science in the 17th century, it has been established by science that there is a complex system of conducting elements in the body. These are human veins, capillaries and arteries. They have a single structural plan, since in the process of embryogenesis they were formed from one germinal leaf - mesoderm. Due to the difference in the functions performed by a certain type of vessels, some structural features appeared in them. In our article, we will focus on the specific properties of arterial vessels involved in the small and large circles of blood circulation.
How the arterial wall is built
Flexible, durable, and flexible tubes that exit the heart are human arteries. Through them, blood moves to all organs and tissues, bringing oxygen to the cells, as well as nutrients: glucose, amino acids, glycerin and fatty acids. At the same time, it takes away the products of cell metabolism and carbon dioxide. In all arterial vessels without exception, blood moves under pressure and at a fairly high speed. To maintain integrity, the walls of the arteries must be very strong. They have a three-layer structure, which we will consider in more detail.
Internal structure
Three vessel shells: external, middle and internal, have differences, which is explained by the functions performed by them. So, the outer layer is represented by loose connective tissue penetrated by nerve endings. The excitation passing through them causes a change in the lumen of the artery, which affects the rate of blood pressure inside the vessel. The middle layer of the artery consists of striated fibers and also contains smooth muscle tissue. In addition to them, connective tissue cords containing protein elastin are present in the arteries. Due to the contraction and relaxation of the muscle layer, the lumen of the vessels changes. It is regulated by the nerve fibers of the autonomic nervous system. So, excitation in the sympathetic section causes a narrowing of the arteries, and in the parasympathetic section - an expansion of their diameter. The inner layer of blood vessels mainly consists of a special connective tissue - the endothelium, has a very smooth surface and provides ideal conditions for the flow of blood through it. As you can see, all layers of the artery wall in the best way perform the function of blood transfer under pressure and at high speed.
Consider the most important arterial vessels in the human body. These include the aorta, pulmonary and coronary vessels.
Aorta
Being the largest artery of our body, the aorta leaves the left ventricle and is divided into three branches: the ascending part, the arc and the descending branch. They provide blood to all internal organs and tissues. The pressure in it is 120-150 mm RT. Art. To withstand constant blows from portions of blood ejected from the heart, the middle layer of the artery consists of powerful muscle tissue that dampens unnecessary vibrations and promotes the passage of blood into a large circle of blood circulation. The rhythmic contractions of the aortic wall can be detected by external palpation of the pulse on the radial artery of the left wrist. Thinning of the muscle layer and loss of elasticity lead to the development of aortic aneurysm - a serious pathology that poses a threat to life and does not have clear symptoms at the initial stages. This complicates early diagnosis, and the disease can be detected using a method such as ultrasound of the arteries.
Pulmonary circulation
Bright scarlet, saturated with oxygen and nutrients, arterial blood moves from the heart through the aorta. From here begins a large circle of blood circulation. Further, due to the division of the aorta into three branches, blood flows to the organs of all physiological systems. There is also a small, so-called pulmonary, circle starting from the right ventricle. A pulmonary artery emerges from it, carrying venous blood into the alveolar vesicles of the lungs, which was collected by the superior and inferior vena cava from a large circle of blood circulation. It must be remembered that on the right side of the heart is venous blood, a portion of which is ejected into the pulmonary artery. The pressure in it is also quite high, although lower than in the aorta.
The middle layer of the artery consists of myofibrils of smooth muscle tissue, alternating with elastic fibers of the protein. Venous blood enters the lungs along the left and right branches of the pulmonary artery, where gas exchange takes place: carbon dioxide enters the alveolar cavity, and oxygen diffuses into the blood, the molecules of which combine with the respiratory pigment - hemoglobin.
As you can see, the pulmonary artery involved in the pulmonary circulation carries venous blood that enters the lungs.
Coronary vessels
The heart is one of the most efficient muscle organs that works rhythmically. It provides blood to the whole body, but also itself needs an uninterrupted supply of trophic substances and oxygen. To carry out its activities, the body has its own vascular system.
It includes the branches of an artery emanating from the initial section of the aorta, called the bulb. The mouths of the coronary vessels are located immediately behind the valves of the aortic valve, which does not allow blood to return back to the left ventricle of the heart. Up to 500 l of blood passes through the coronary vessels per day, this indicates the large loads that the blood supply to the heart undergoes. The middle layer of the artery consists of muscle and elastic fibers and, due to the development of atherosclerosis or with frequent sharp spasms, can lose elasticity. The lumen of the vessel decreases, which provokes necrosis of the heart muscle area - myocardial infarction.
Blood pressure
Earlier, we found that in arteries, blood moves under pressure and at high speed. Blood pressure is associated with phases of cardiac activity: systole and diastole, and with normal vascular tone is approximately equal to 120/70 mm RT. Art. It is measured by a manometer on the brachial artery. If the walls of the arteries narrow, their tone increases and the pressure increases. This pathological condition is called hypertension. It leads to a load of the heart muscle, impaired blood circulation and without proper treatment can cause a heart attack.
In this article, we studied the structure of arteries and established the features of their functioning in the human body.