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Cardiac Cycle- Human heart, Functions, Blood circulation, Double circulation

The heart is the muscular organ that pumps blood throughout the body tissues and organs. Its function is to circulate oxygen and other nutrients throughout the body. However, the performance of the heart depends on the cardiac cycle. In this article, we will be discussing the human heart, its function, and structure along with the cardiac cycle in detail.

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Posted by Kunduz Tutor, 26/10/2021
Cardiac Cycle- Human heart, Functions, Blood circulation, Double circulation

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As we all know, the heart is an important organ that transports oxygen throughout the body tissues and removes carbon dioxide from the same, via blood circulation. The performance of the heart depends on the cardiac cycle. Let us learn more about the human heart- structure, and function. Moreover, we will learn about the cardiac cycle in detail.

Author – Parisa Gupta

The heart

“The heart is a muscular organ that pumps blood throughout the body tissues and organs.”

Heartbeat is the movement of the heart that typically sounds like lub-dub. This is due to the contraction and relaxation of the heart muscles.

labelled diagram of human heart
Labelled parts of the human heart

Structure and working of the human heart

  1. Our heart has four chambers: two atria (singular: atrium) and two ventricles. The right atrium receives deoxygenated blood from the body parts through the vena cava.
  2. When the right atrium contracts blood enters the right ventricle through the tricuspid valve.
  3. The right ventricle then sends this blood to the lungs through the pulmonary artery.
  4. The left atrium receives oxygenated blood from the lungs through the pulmonary vein and sends it to the left ventricle on contraction through the mitral valve.
  5. From the left ventricle, the blood enters the aorta and reaches different parts of the body.

Human beings have a four-chambered heart and there is no intermixing of oxygenated and deoxygenated blood this allows an efficient supply of oxygen to the blood. As a result, it helps them in having high energy, which is essential to maintain their body temperature.

What is double circulation of blood?

Doube circulation is a characteristic feature of the human heart. It is the process, during which, blood passes through the heart twice in one cardiac cycle.

What is cardiac cycle?

“Cardiac cycle is the performance of human heart from the beginning of one heartbeat to the beginning of the next.”

Furthermore, a single cycle of cardiac activity consists of two basic phases:

  1. Diastole
  2. Systole.

Diastole and systole of a cardiac cycle:

Diastole represents the period when the ventricles relax. Whereas, systole represents the time during which the left and the right ventricle contract and eject blood into the aorta and pulmonary artery respectively.

Electrocardiography helps in recording the systolic and diastolic movement, whereas an electrocardiogram helps in representing it in the form of waves.

In addition, the events of the cardiac cycle consist of:

  1. Atrial event
  2. Ventricular events

Atrial events are further divided into atrial systole and atrial diastole while the ventricular events are divided into ventricular systole and ventricular diastole

Furthermore, the divisions occur as follows:

  1. Ventricular systole is divided into Isometric contraction and Ejection period
  2. Ventricular diastole is divided into protodiastole, isometric relaxation, rapid filling, slow filling, and last rapid filling.

Heart of other animals

Amphibians and reptiles have a three-chambered heart so they show partial intermixing of oxygenated and deoxygenated blood.

Whereas, fishes have a two-chambered heart so the blood goes only once through the heart during one circulation cycle.


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