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After reading this article you will learn about the structure of human heart. This will also help you to draw the structure and diagram of human heart.
The Heart lies in the thoracic cavity between the two lungs in the mediastinal space and behind the sternum. It is directed more to the left than to the right side. The anterior surface of the heart faces the sternum, the posterior surface faces the vertebral column and the interior surface rests on diaphragm. The heart is composed of a specialized cardiac muscle which possesses the special property of automatic rhythmical contraction.
The heart is consisting of three layers:
1. Pericardium or outer covering layer:
The heart lies in a double membranous sac of pericardium with serous fluid between the two layers. This is known as pericardial fluid. By its lubricating action, the heart can move freely or contracts and expands without any injury. So it allows the easy movement of the heart. It keeps the heart moist and absorbs external shock.
2. The Myocardium:
This is the middle muscular layer. The thickness of the heart wall is composed of a network of heart muscle fibers which is known as myocardium. The muscular walls of the heart very in thickness. The ventricles have the thickest walls. The walls of the left ventricles are thicker then those of right ventricle because the force of contraction of the left ventricle is much greater. The walls of the auricle are composed of thinner muscles.
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3. The Endocardium:
This is the inner layer of the heart. The heart is lined by endothelium layer which is known as Endocardium. The valves attached to the heart are the thickened portions of this membranes.
Auricles and Ventricles:
The heart is divided by a septum into two sides right and left. These two parts are automatically joined together, but physiologically separate. There is normally no communication between these sides after birth.
Each side of the heart consists of two chambers:
(1) An upper thin walled atrium or auricle and
(2) The lower thick walled chamber called as ventricle.
There are two auricles or atrium right and left and two ventricles. The auricles act as receiving chambers and the ventricles the pumping chambers. The auricles and ventricles of each side communicate with one another by means of the auriculo-ventricular openings. These openings are guarded by valves which permit blood to flow from auricles to the ventricles but not in the opposite direction – that is from ventricle to auricles.
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On the right side, the auriculo-ventricular opening is guarded by tricuspid valve which is composed of three flaps and on the left side by the bicuspid valve which is composed of two flaps. When the auricles are contracted, the tricuspid and bicuspid valves open and blood enters into the ventricles. But when ventricles are contracted, the flaps in the valves open like umbrella and close the auriculo ventricular openings, so that blood cannot pass back again to the auricles.
The blood in the ventricles is forced to go into the respective blood vessels which arise from them, the pulmonary artery from right ventricle and aorta from the left ventricle. The opening leading to the pulmonary artery and the aorta are guarded by different types of valves which are called semilunar valves. These valves permit the blood to enter these arteries. They prevent back flow of blood.
Two large veins named superior vena cava and inferior vena cava are attached to the right auricle which brings impure or deoxygenated blood from all parts of the body. The left auricle is attached with four pulmonary veins which carry pure or oxygenated blood from the lungs.
