Circulatory system

The circulatory system is a complex closed network that includes two circles (venous and arterial or small and large) of the circulation and a "central pump" - the heart.

All vessels are divided into veins, the smallest vessels (capillaries) and arteries. The latter perform the function of reporting 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 dissolve into smaller ones (arterioles), which in turn form a network of the thinnest capillaries. They absorb waste and produce useful products and oxygen. Through the capillaries, the arterioles are connected to the veins in the tissues.

The venous circulatory system is responsible for producing an outflow of carbon- rich blood. On these vessels the blood returns to the heart. Medium and small veins have valves that prevent the return (reverse) of blood.

The heart is represented by a hollow muscular organ with four chambers. It includes two atria (receiving chambers) and two ventricles, which act as pumps. In the heart there is a dividing vertical partition. The left ventricle and the left atrium are delimited by a two-fold valve, the right ventricle and the right atrium are a three-leaf valve. To the valve flaps, the tendon threads are attached from the ventricular side. The task of the valves is to prevent the reverse movement of blood.

The heart is surrounded by a strong connecting bag - the pericardium.

As mentioned above, the circulatory system includes two circles of circulation. However, experts often speak about the third - the heart circle. It is distinguished due to its importance, since it is responsible for providing the myocardium. The beginning of the circle lies in two coronary arteries, departing from the base of the ascending aorta. Entering the cardiac myocardium, they form a network of small arteries. Myocardium is characterized by a fairly strongly developed network of capillaries, which provides replaceable processes in this muscle tissue. From the myocardium venous blood flows into the right heart part through numerous coronary veins. With the contraction of the heart muscle, blood pressure is created. Due to it, arterial blood moves.

A large circle originates in the left ventricle. The contraction of the heart muscle promotes the movement of arterial blood towards the aorta, and then all organs and tissues. In this case, the supply of nutrients and oxygen and the saturation of blood with products of cellular life and carbon dioxide take place. Blood is collected in the veins through the capillaries. Through the upper and lower veins, it enters the right atrium, closing a large circle.

A small circle originates in the right ventricle. Blood from the vein, entering the right atrium, flows into the right ventricle, from which it enters the artery of the lungs. Passing through the pulmonary capillaries, it is released from carbon dioxide and, being saturated with oxygen, becomes arterial and flows into the left atrium.

The phylogeny of the circulatory system in all vertebrates is identical. The structure of this system includes the aorta, microcirculatory bed (including the capillary network), arteries, heart and veins. In this process, the lymphatic network was isolated during evolution. 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), as a rule, are treated according to the type of affected vessels. So, for example, stretching in the vascular walls provokes aneurysms. In the aorta, atherosclerotic or infectious processes often develop. Its rupture can occur due to congenital weakness of the walls or trauma. In pulmonary arteries arteriosclerotic changes may occur or congenital pathologies may occur. The middle arteries often affects atherosclerosis. In the veins, varicose veins or inflammation (phlebitis) often occur.