HUMAN ANATOMY AND PHYSIOLOGY

 1.Right Atrium::

It is above and to the right of the heart it has thin walls with an appendage called the auricle Superior venacava brings deoxygenated blood from upper part of the body whereas inferior venacava brings deoxygenated blood to the right atrium from the lower part of the body Besides these two openings there is an opening of the coronary sinus which brings the blood from the coronary vein of the heart muscle 

2.Right Ventricle:

This ventricle is on the right side Right ventricle has thick walls as compared to right atrium but it is thinner than the walls of the left ventricle It opens to the pulmonary trunk This trunk carries blood to the lungs for oxygenation The pulmonary trunk divides into two branches the right pulmonary artery that passes to the right lung and the left pulmonary artery that passes to the left lung for pulmonary circulation 

        The pulmonary trunk has a semilunar valve with three curved semilunar cusps This valve closes to prevent the back flow into the right ventricle at the start of the ventricular diastole There is a big opening between the right atrium and the right ventricle called the right atrioventricular opening an aperture with a ring  and a tricuspid valve guarding the right atrioventricular opening This valve prevents the back entry of blood into the right atrium in the beginining of the systole the papillary muscles in the ventricle prevent over distension of the valve during the diastole 

3.Left Atrium::

It is situated not to the left as much as it is to the back of the heart it has thin walls like that of the right atrium There are four opening of the four pulmonary veins two on each side They bring oxygenated blood to the left atrium to pour it into the left ventricle 

4.Left Ventricle::

This is situated on the anterior aspect of the left side of the heart The apex of the heart is formed by the tip of the left ventricle The walls of the left ventricle are three times thicker than the right ventricle since it has to pump the blood all over the body which is named as systemic circulation