Question

Как осущ. работа сердца?Раскройте особенности фаз сердечного цикла.

Answer 1

How does the heart work?

The heart is a vital organ responsible for pumping blood throughout the body. It consists of four chambers: two atria and two ventricles. The atria receive blood from the body and lungs, while the ventricles pump blood out to the body and lungs.

The heart works through a series of coordinated contractions and relaxations, known as the cardiac cycle. This cycle consists of two main phases: diastole and systole.

During diastole, the heart is in a relaxed state, and the atria fill with blood from the body and lungs. The atria contract, pushing blood into the ventricles. This phase is known as atrial systole.

Next, the ventricles contract, pushing blood out of the heart. This phase is known as ventricular systole. The right ventricle pumps blood to the lungs for oxygenation, while the left ventricle pumps oxygenated blood to the rest of the body.

After ventricular systole, the heart enters a brief period of rest called isovolumetric relaxation. During this phase, all four heart chambers are relaxed, and the heart refills with blood.

The cardiac cycle repeats continuously, ensuring a constant flow of blood throughout the body.

Phases of the Cardiac Cycle

1. Atrial Contraction (Atrial Systole): The atria contract, pushing blood into the ventricles. This phase accounts for about 20-30% of ventricular filling.

2. Isovolumetric Contraction: The ventricles begin to contract, but the pressure is not yet sufficient to open the semilunar valves. This phase is called isovolumetric because the volume of blood in the ventricles remains constant.

3. Ventricular Ejection: The pressure in the ventricles exceeds the pressure in the arteries, causing the semilunar valves to open. Blood is ejected from the ventricles into the pulmonary artery and aorta.

4. Isovolumetric Relaxation: After ventricular ejection, the ventricles relax, and the semilunar valves close. The atria begin to fill with blood again, but the ventricles remain closed. This phase is called isovolumetric because the volume of blood in the ventricles remains constant.

5. Rapid Ventricular Filling: The pressure in the atria exceeds the pressure in the ventricles, causing the atrioventricular (AV) valves to open. Blood rapidly fills the ventricles.

6. Diastasis: The ventricles continue to fill with blood at a slower rate. This phase is called diastasis.

7. Atrial Kick: The atria contract again, pushing the remaining blood into the ventricles before the next cycle begins.

It's important to note that the duration of each phase can vary depending on factors such as heart rate and overall cardiovascular health.

In summary, the heart works by going through a series of contractions and relaxations known as the cardiac cycle. This cycle consists of phases such as atrial contraction, ventricular ejection, and rapid ventricular filling. These phases ensure a continuous flow of blood throughout the body.