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145
The Cardiovascular System
atrium
chambers
coats
heart
lungs
pericardium
portal
valves
veins
The (1) is an inner hollow muscular organ placed within the chest and
included in the (2). 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 (3) divided by the septum. Each of the
chambers has two connected parts: the (4) and the ventricle. The atrioventricular
(5) 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 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 of each ventricle.
The muscular structure of the heart consists of fibrous bands divided into
two groups — the first ones are the fibrous bands of the atria and the second
ones are the fibrous bands of the ventricles.
The vascular system consists of three groups of vessels - arteries, (6) and
capillaries.
The vessels carrying blood to and from the tissues of the body compose
tne general system. They are called the systemic vessels.
The pulmonary system is formed by the vessels carrying blood to and from
the (7).
The (8) system is formed by the veins passing to the liver.
Most of the arteries are composed of three (9). The arteries dilate and
contract simultaneously with the action of the heart.