The heart’s function is to pump blood through the blood vessels. The heart beats rhythmically. The walls of the heart are formed by muscle tissue, the muscle walls of the ventricles are especially well developed. By contracting, the ventricles push blood with great force into the vessels of the circulation. From the left ventricle, blood enters the aorta, then enters the vessels of the systemic circulation and is carried throughout the body. Therefore, the walls of the left ventricle are thicker than the walls of the right ventricle.
With each contraction of the left ventricle, the blood strikes with force against the elastic walls of the aorta and stretches them. The wave of elastic vibrations arising in this case quickly spreads along the walls of the arteries. Such rhythmic oscillations of the vessel walls are called a pulse. Each beat of the pulse corresponds to one heartbeat. By counting the pulse, you can determine the number of heart contractions in 1 min. The average human heart rate (HR) at rest is about 75 beats per minute.
The pulse can be felt on the surface of the body in those places where large vessels lie close to the surface of the body: on the temples, on the inner side of the wrist, on the sides of the neck.
The work of the heart to pump blood is cyclical. The contraction of the heart is called systole, and relaxation is called diastole.
One cardiac cycle (a sequence of processes occurring in one heartbeat (systole) and its subsequent relaxation (diastole)) lasts 0.8 s. (three phases):
- 0.1 sec. takes a contraction (systole) of the atria (phase I),
- 0.3 sec. – contraction (systole) of the ventricles (phase II),
- 0.4 sec. – general relaxation (diastole) of the whole heart – general pause (phase III).
During atrial systole, the pressure in them increases and blood flows through the relaxed leaflet valves into the ventricles.
This is followed by a contraction of the ventricles. The leaflet valves close and prevent blood from flowing back into the atria. Therefore, blood from the ventricles enters through the open semilunar valves into the vessels of the circulatory system. From the left ventricle, blood flows through the aorta into the systemic circulation, and from the right through the pulmonary artery into the pulmonary (small) circle of blood circulation.
Then the ventricles relax, the semilunar valves close and block the flow of blood back from the vessels to the ventricles.
When the atria and ventricles contract, murmurs or heart sounds occur.
Violation of the heart leads to a change in these tones. Doctors listen to the heart and can determine the diagnosis by its tones.
Automation is the ability of the heart to contract regardless of external conditions under the influence of impulses that arise in it.
The heart contracts under the influence of impulses that arise in the nodes of automation – in groups of special muscle cells. The main automation node is located in the right atrium. It is here that impulses arise that determine the rhythm of heart contractions.
Regulation of the cardiovascular system
There are two ways to regulate the work of the heart and blood vessels: nervous and humoral.
- The autonomic nervous system plays a major role in nervous regulation.
- Humoral regulation is carried out by substances entering the blood. So, the work of the heart is accelerated by the hormone adrenaline and an excess of calcium ions, and an excess of potassium ions, on the contrary, slows down its work.