Cardiac cycle definition
A cardiac cycle is a period that begins with the atria contracting and ends with ventricular relaxation.
From the moment a heartbeat is produced until the next beat begins, it is called the cardiac cycle. It consists of diastole, systole, and the pause in between. A heart rate, which is naturally expressed in beats per minute, depicts a cardiac cycle. The heart of a healthy human being beats 72 times per minute or 72 cardiac cycles per minute. The cardiac cycle lasts about 0.8 seconds and involves complete contraction and relaxation of both the atria and ventricles.
Cardiac cycle classification
The different phases that are there in the cardiac cycle are as follows:
Atrial Diastole: The heart’s chambers are calmed during this stage. The aortic valve and pulmonary artery close, while the atrioventricular valves open, causing the heart chambers to relax.
Atrial Systole: Blood cells flow from the atrium to the ventricle during this phase and the atrium contracts. When the atrium is in the process of contracting, during joint diastole, 70 to 80 percent of blood will flow from the atria to the ventricles, leaving only 20 to 30 per cent in the atria. To pump this blood out, the atria will exert some force. The contraction phase of the atria, also known as an arterial system, causes this contraction as the SA node transfers its impulses; then, the contraction phase in the atria occurs.
Isovolumic Contraction: The ventricles begin to contract at this point. The atrioventricular valves and pulmonary artery valves all close, but there is no volume change.
Ventricular Ejection: In this stage, the ventricles contract and empty. The aortic valve and the pulmonary artery close.
Isovolumic Relaxation: No blood enters the ventricles during this phase, so pressure drops, ventricles stop contracting, and they start to relax—the pulmonary artery and aortic valve close due to the pressure in the aorta.
Ventricular Filling Stage: Blood flows from the atria into the ventricles during the Ventricular Filling Stage. It is referred to as a single-stage (first and second stage). The flow of blood from the ventricles to the pulmonary artery is divided into three phases.
Human Heart and the Cardiac Cycle
The heart is a powerful pumping organ that transports blood from the heart to the rest of the body via the circulatory system. The heart is a pump that circulates blood throughout the body. The triangular portion’s superior-broad portion is tilted to the right, while the narrow lower portion is tilted to the left. The three layers of the heart wall are endocardium, myocardium and epicardium. Two pericardial membranes (pericardium) membranes surround the heart. The pericardial membrane is a protective layer that covers the heart’s outer surface. The fluid that fills the space between the two membranes is known as pericardial fluid.
There are four chambers in the human heart. Auricles (atria) are two upper chambers, while ventricles are two lower chambers.
Auricle on the right (Atrium)
The superior vena cava, the inferior vena cava, and the coronary sinus openings in the right auricle. The superior vena cava transports deoxygenated blood from the head, neck, and upper limbs to the right auricles. In contrast, the inferior vena cava transports blood from the rest and lower limbs. The coronary sinus auricle blood passes through a tricuspid valve into the right ventricle.
The ventricle of the right heart
A semilunar valve protects it.
Auricle on the left
Four pulmonary veins enter this chamber. A bicuspid valve allows the blood from the left auricle to flow into the left ventricle.
Ventricle on the left
Coronary veins that join to form the coronary sinus return this blood to the heart.
Duration of the Cardiac Cycle
The heartbeat of a healthy person is 72 beats per minute. As a result, the length of a cardiac cycle can be calculated as follows:
1/72 beats per minute equals .0139 minutes per beat
Each cardiac cycle will last 0.8 seconds at a heart rate of 72 beats per minute.
The following are the durations of the various stages of the cardiac cycle:
- For about 0.1 seconds, atrial systole continues
- Ventricular systole lasts approximately 0.3 seconds
- The atrial diastole lasts about 0.7 seconds
- Ventricular diastole lasts approximately 0.5 seconds