The circulation of the blood

The venous blood from systemic and portal circulation is brought to the right atrium of the heart. When the pressure in the right atrium has increased the blood passes into the right ventricle from the right atrium.

During the systole of the ventricle the blood is pumped from the tight ventricle into the pulmonary artery and blood enters the pulmonary circulation. In the lungs the venous blood discharges out carbon dioxide and takes in oxygen in the lungs. Then blood passes into the venules and veins. When the oxygenated blood passes the 4 pulmonary veins it’s brought to the left atrium of the heart. Under the pressure in the left atrium the arterial blood is pumped into the left ventricle. During the so-called ventricular systole the blood is pumped into the aorta – the main artery of the vascular system. Then blood is carried through the arteries to all parts of the body.

The corpuscular elements of blood

Blood is a fluid tissue with many various functions. Not only important physiological process takes place in the blood but it determines the activity of widely separated body cells.

Blood is composed of plasma and the corpuscular elements which are called red corpuscles (erythrocytes), white corpuscles (leucocytes), and blood platelets (thrombocytes).

The count of leucocytes in the blood of a healthy person is 4,500 to 9,500 per cu mm. when the number of white blood cells (WBC) is counted after mental or physical exertion, meals and mild activity it may increase to 10,000 and more per cu mm.

The erythrocytes are the most numerous cellular elements, ranging from 4,000,000 to 5,000,000 per cu mm. The RBC may change with age, after physical exertion and emotions. The red blood cells have 2 physical features which are very important in the function of respiration. They have great elasticity and flexibility. These features give them the possibility to pass through very small capillaries. The discoid form gives them a maximal surface for a given mass.

The most important part of the red cell is its red colouring substance or hemoglobin which on an average forms about 36% of its mass.

The cardiac rhythm

During the diastole the atria and ventricles take in the blood. But during the systole the atria and the ventricles discharge out the blood. The diastole of the ventricles takes place during the systole of the atria, and the systole of the ventricles takes place during the diastole of the atria. These functions of the atria and the ventricles compose the cardiac rhythm.

The cardiac cycle lasts 0,9 second. When the atria contract, the ventricles are at rest.

The period of contraction of the ventricles is longer than that of the atria and the systolic blood pressure is always higher than the diastolic one. Such an interesting cardiac rhythm, which enables the heart to rest longer than to work, is very important for the blood circulation.

If the period of cardiac rest has become constantly shorter, the rate of heartbeat increases. Such an increased rate of heartbeat may affect the heart and produce different cardiac diseases.