The Cardiac cycle:
the function of the heart is to maintain a constant circulation of blood throughout the body. It acts as a pump to maintains a constant circulation of blood throughout the body. It’s achieved as follows:
The functions of the cardiovascular system are to provide the tissues of the body with oxygen and nutrients which are transported in the blood. The superior and inferior vena cava veins bring venous blood from various body parts to the heart. This venous blood fills the right atrium. When it’s full, the right atrium contracts sending blood to the right ventricle. Now the right ventricle contracts this sends blood to the lungs through pulmonary trunk which divides into right and left pulmonary arteries. The blood gets oxygenated in the lungs and then the oxygenated blood is carried by a pulmonary vein to the left atrium. Now the left atrium contracts and sends blood to the left ventricle. The left ventricle contracts and send blood into the aorta, this blood circulated throughout the body. This is achieved by rhythmic contraction of its muscle. The cardiac cycle is the sequence of events which occur in the heart during a single beat. Heart rate is between 60 to 90 normally. With an average rate of 72. So the time taken for one beat is 0.8 second. So the sequence of events occurs every 0.8 seconds.
The cardiac cycle occurs in 2 phases:
- Systole which means a period of contraction.
- Diastole which means a period of relaxation.
The cycle of events occurs as follows:
- To start with blood from the veins fill the 2 atria, the superior and inferior vena cava fill the right atrium, the pulmonary veins fill the left atrium.
- This is followed by a wave of contraction in the atria, this leads to emptying of atrial blood into the respective ventricle.
- When the ventricles are full, they contract, now the blood present in ventricles is forced into systemic and pulmonary circulation. At this stage, the semilunar valves guarding the aorta and pulmonary arteries are opened. At the same time, the atrioventricular are opened. At the same time, the atrioventricular valves are closed. This period of muscular contraction of the heart is called systole.
- This is followed by a period of relaxation called diastole during which there’s no contraction.
- This sequence of events constitutes the cardiac cycle.