By contracting, the heart works like a pump and pushes blood through the vessels, ensuring its continuous movement. When it stops, death occurs, since the delivery of oxygen and nutrients to the tissues, as well as their release from decay products, stops.
In an adult, the heart is a hollow muscular organ weighing 250–300 g. It is located behind the chest cavity behind the sternum, slightly to the left of it.
The heart is located in a special pericardial sac made of connective tissue (pericardium). The inner surface of the pericardium (sac) secretes fluid that hydrates the heart and reduces friction during contractions.
The wall of the heart consists of three layers, the most developed of which is the middle muscle layer – the myocardium. The fibers of muscle tissue are connected to each other. Therefore, the excitement that occurs in one part of the heart is quickly transmitted throughout the heart muscle, and it contracts, pushing out the blood.
The human heart (like all mammals) has four chambers.
It is divided by a solid partition into two parts – right and left (venous blood flows in the right half of the heart, arterial in the left).
The right and left halves of the heart are divided by an incomplete septum into two communicating sections: the upper section – the atria (right and left atria) and the lower section – the ventricles (right and left ventricles).
The atria are separated from the ventricles by cuspid valves. There is a bicuspid (mitral) valve in the left half of the heart, and a tricuspid valve in the right.
Through the valves, blood passes from the atrium to the ventricle, but not back!
From the left ventricle comes the largest artery – the aorta, from the right ventricle – the pulmonary artery. At the exit from the ventricles in these large vessels are the semilunar valves.
Blood is pushed out of the heart through the semilunar valves from the left ventricle (through the aorta) into the large circle, and from the right (through the pulmonary artery) into the pulmonary circulation. The semilunar valves are designed to allow blood to flow in only one direction (from the heart).
Coronary system of the heart
The heart muscle requires a lot of nutrients and oxygen to work. Therefore, it is well supplied with blood through the coronary system. The system is formed by two coronary arteries that extend from the aorta. Arteries branch into smaller vessels and deliver all the necessary substances to the heart muscle