Give a description of the external and internal structure of the heart.

The human heart has the shape of a truncated cone, approximately the size of an individual’s clenched fist, the mass of the organ is 240-310 g (in women and men, respectively).

There are 4 cavities in the heart: two atria and two ventricles, which do not communicate with each other. Between the atria and the ventricles – leaflet valves (tricuspid – in the right half, bicuspid, mitral – in the left).

In the right atrium there are two openings where the hollow veins flow, in the left atrium there are 4 openings (for the pulmonary veins). The pulmonary trunk departs from the right ventricle, the aorta departs from the left ventricle, and the semilunar valves between the heart and these vessels.

The heart consists of three membranes – epicardium, myocardium, endocardium. It is covered with a heart sac – the pericardium, between it and the heart – a cavity filled with fluid (to soften the friction of surfaces). The heart has its own conducting system, which ensures its autonomous work.