short note on structure of human heart for class 11
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External Structure of Heart
One of the very first structures which can be observed when the external structure of the heart is viewed is the pericardium.
Pericardium
The human heart is situated to the left of the chest and is enclosed within a fluid-filled cavity described as the pericardial cavity. The walls and lining of the pericardial cavity are made up of a membrane known as the pericardium.
The pericardium is a fibre membrane found as an external covering around the heart. It protects the heart by producing a serous fluid, which serves to lubricate the heart and prevent friction between the surrounding organs. Apart from the lubrication, the pericardium also helps by holding the heart in its position and by maintaining a hollow space for the heart to expand itself when it is full. The pericardium has two exclusive layers—
Visceral Layer: It directly covers the outside of the heart.
Parietal Layer: It forms a sac around the outer region of the heart that contains the fluid in the pericardial cavity.
Structure of the Heart Wall
The heart wall is made up of 3 layers, namely:
Epicardium – Epicardium is the outermost layer of the heart. It is composed of a thin-layered membrane that serves to lubricate and protect the outer section.
Myocardium – This is a layer of muscle tissue and it constitutes the middle layer wall of the heart. It contributes to the thickness and is responsible for the pumping action.
Endocardium – It is the innermost layer that lines the inner heart chambers and covers the heart valves. Furthermore, it prevents the blood from sticking to the inner walls, thereby preventing potentially fatal blood clots.
Internal Structure of Heart
The internal structure of the heart is rather intricate with several chambers and valves that control the flow of blood.
Chambers of the Heart
Vertebrate hearts can be classified based on the number of chambers present. For instance, most fish have two chambers, reptiles and amphibians have three chambers. Avian and mammalian hearts consists of four chambers. Humans are mammals; hence, we have four chambers, namely:
Left atrium
Right atrium
Left ventricle
Right ventricle
Atria are thin, less muscular walls and smaller than ventricles. These are the blood-receiving chambers that are fed by the large veins.
Ventricles are larger and more muscular chambers responsible for pumping and pushing blood out to the circulation. These are connected to larger arteries that deliver blood for circulation.
The right ventricle and right atrium are comparatively smaller than the left chambers. The walls consist of fewer muscles compared to the left portion, and the size difference is based on their functions. The blood originating from the right side flows through the pulmonary circulation, while blood arising from the left chambers is pumped throughout the body.
Structure of the Human Heart
The human heart is about the size of a human fist and is divided into four chambers, namely two ventricles and two atria. The ventricles are the chambers that pump blood and atrium are the chambers that receive blood. Among which both right atrium and ventricle make up the “right heart,” and the left atrium and ventricle make up the “left heart.” The structure of the heart also houses the biggest artery in the body – the aorta. The right and the left region of the heart are separated by a wall of muscle called the septum. The right ventricle pumps the blood to the lungs for re-oxygenation through the pulmonary arteries. The right semilunar valves close and prevent the blood from flowing back into the heart. Then, the oxygenated blood is received by the left atrium from the lungs via the pulmonary veins. Read on to explore more about the structure of the heart.