Text A. The Heart and the Vascular

Text A. The Heart and the Vascular System
The heart is an inner hollow muscular organ placed within the chest and included in the pericardium. The base of the heart is against the third rib. Its apex is against the interspace between the fifth and sixth costal cartilages. The weight of the heart is about 300 grams (gr) in the male and about 220 gr in the female.
The heart consists of two separate chambers divided by the septum. Each of the chambers has two connected parts: the atrium and the ventricle. The atrioventricular valves separate the atria from the ventricles.
The right atrium is larger than the left one, but the walls of the left atrium are thicker than those of the right one. The right ventricle is triangular (треугольный) in form and has thick walls. The right ventricle is in the anterior part of the heart. The left ventricle is longer and more conical than the right one. The walls of the left ventricle are three times as thick as the walls of the right one. The valves are located at the entrance and exit (выход) of each ventricle.
The muscular structure of the heart consists of two parts — the muscular layers of the atria and the muscular layers of the ventricles.
The vascular system consists of three groups of vessels — arteries, veins and capillaries.
The vessels carrying blood to pand from the tissues of the body compose the general circulation. They are called the systemic vessels.
The pulmonary circulation is formed by the vessels carrying blood to and from the lungs.
The portal system is formed by the veins passing to the liver.
Most of the arteries are composed of three coats. The arteries dilate and contract simultaneously with the action of the heart.