The circulatory system is a complex closed network that includes two circles (venous and arterial or small and large) of blood circulation and the “central pump” - the heart.
All vessels are divided into veins, the smallest vessels (capillaries) and arteries. The latter perform the function of delivering oxygen-enriched, "clean" blood to organs and tissues. Arteries are the most numerous vessels in which the muscular membrane is quite developed. The arterial circulatory system includes large vessels that break up into smaller vessels (arterioles), which, in turn, form a network of the thinnest capillaries. They absorb waste and release healthy products and oxygen. Through capillaries, arterioles are combined with veins in the tissues.
The venous circulatory system is responsible for producing an outflow of blood saturated with carbon dioxide . Through these vessels, blood returns to the heart. Medium and small veins have valves that prevent the return (reverse movement) of blood.
The heart is represented by a hollow muscular organ with four chambers. It includes two atria (reception chambers) and two ventricles that act as pumps. In the heart there is a dividing vertical partition. The left ventricle and the left atrium are delimited by a bicuspid valve, the right ventricle and the right atrium are distinguished by a tricuspid valve. Tendon sutures are attached to the valve cusps from the ventricular side. The purpose of the valves is to prevent the reverse movement of blood.
A strong connecting bag - the pericardium surrounds the heart.
As mentioned above, the circulatory system includes two circles of blood circulation. However, experts often talk about the third - the heart circle. It is isolated because of its importance, as it is responsible for providing the myocardium. The beginning of the circle lies in two coronary (coronary) arteries extending from the base of the ascending aorta. Entering the cardiac myocardium, they form a network of small arteries. The myocardium is characterized by a rather strongly developed network of capillaries, which provides interchangeable processes in this muscle tissue. From the myocardium, venous blood flows into the right heart through numerous coronary veins. When the heart muscle contracts, blood pressure is created. Due to it, the movement of arterial blood occurs .
The large circle originates in the left ventricle. Contraction of the heart muscle promotes the movement of arterial blood toward the aorta, and then all organs and tissues. In this case, the return of nutritious products and oxygen and the saturation of the blood with products of cellular vital activity and carbon dioxide. Blood collection occurs in the veins through the capillaries. Through the superior and inferior veins, it enters the right atrium, closing a large circle.
The small circle originates in the right ventricle. Blood from a vein entering the right atrium flows into the right ventricle, from which it enters the pulmonary artery. Passing through the pulmonary capillaries, it is freed from carbon dioxide and, saturated with oxygen, becomes arterial and flows into the left atrium.
The phylogenesis of the circulatory system in all vertebrates is identical. The structure of this system includes the aorta, microvasculature (including the capillary network), arteries, heart and veins. Moreover, in the process of evolution, isolation of the lymphatic network was observed. The main changes in the structure of the circulatory system include the transition of the type of respiration from the gill method to the pulmonary method.
Diseases of the circulatory system (vascular diseases) are usually treated according to the type of affected vessels. So, for example, sprains in the vascular walls provoke aneurysms. Atherosclerotic or infectious processes often develop in the aorta. Its rupture can occur due to congenital weakness of the walls or trauma. In the pulmonary arteries, arteriosclerotic changes may occur or congenital pathologies may occur. The middle artery often affects atherosclerosis. Varicose veins or inflammation (phlebitis) often occur in the veins.