During the cardiac cycle, the heart progresses between systole and Multiple Choice cardiac cycle. systole. pulse. diastole.
The correct answer and explanation is:
The correct answer is diastole.
Explanation:
The cardiac cycle consists of two main phases: systole and diastole. These phases describe the rhythmic contraction and relaxation of the heart muscle, which is essential for pumping blood throughout the body.
- Systole refers to the phase of the cardiac cycle when the heart muscles contract. During systole, the ventricles (the lower chambers of the heart) contract, forcing blood out of the heart into the arteries. Specifically, the left ventricle pumps oxygenated blood into the aorta to supply the body, while the right ventricle pumps deoxygenated blood into the pulmonary artery to reach the lungs for oxygenation. This contraction increases the pressure inside the ventricles, closing the atrioventricular valves (mitral and tricuspid valves) and opening the semilunar valves (aortic and pulmonary valves) to allow blood flow out of the heart.
- Diastole is the phase of the cardiac cycle when the heart muscles relax. After systole, the ventricles relax and expand, reducing the pressure inside them. This causes the semilunar valves to close, preventing blood from flowing back into the ventricles. During diastole, the atrioventricular valves open, and blood flows passively from the atria into the ventricles, filling them in preparation for the next contraction. Diastole is also when the coronary arteries receive blood, providing oxygen and nutrients to the heart muscle itself.
The heart alternates between these two phases continuously, creating the heartbeat. The coordinated contraction and relaxation ensure efficient circulation of blood, delivering oxygen and nutrients to tissues and removing waste products.
In summary, systole is the contraction phase, and diastole is the relaxation and filling phase of the cardiac cycle. The alternation between these phases maintains the vital function of the heart as a pump and keeps blood flowing effectively through the cardiovascular system. The other options—pulse and cardiac cycle—are not phases but rather concepts related to heart function: the pulse is the tactile arterial pressure wave felt with each heartbeat, and the cardiac cycle is the entire sequence of systole and diastole.