Name: Lymphatic System: An Overview
Uploaded: 2019-07-19
Duration: 2 min 47 s
Description: There are two types of liquid that run inside your body - the first is the blood and the other lymph. We all know about blood, but what is lymph? Find out in...

Question

Describe the structure of human heart and discuss about the mechanism of circulation.

Accepted Answer

The circulation is closed and double in the body of a human. The heart plays an essential role in the circulation in body of a human. The human heart is myogenic in nature. The human heart is derived from the mesoderm layer of the embryo.

Structure of the heart:

The heart is a conical muscular pumping organ, present in the middle mediastinum of the thoracic cavity. It is enclosed by a pericardium. The pericardium is a fibrous sac surrounding the heart and the roots of great vessels. It consists of outer fibrous and inner serous layers. The fibrous pericardium is a tough connective tissue outer layer that defines the boundary of the middle mediastinum. The serous pericardium, also known as the epicardium, consists of the outer parietal layer and inner visceral layer. Both the layers are continuous at the roots of great vessels. There is a pericardial fluid in the space between the parietal and visceral layers. This fluid protects the heart from friction, caused during its contraction and relaxation The shape of the heart is conical or pyramidal. The shape is comparable to that of a pyramid that has fallen over and is resting on one side. The apex projects forward, downward, and to the left. The heart is four-chambered consisting of two atria and two ventricles. Internally, the chambers are separated from each other by partitions. These partitions conform to the external grooves, called sulci (singular; sulcus). The atria are separated from the ventricles by a coronary sulcus. This groove harbours the coronary sinus, cardiac vein, right coronary artery, and a branch of the left coronary artery. The ventricles are separated from each other by anterior and posterior inter-ventricular sulci.

Mechanism of circulation

At first the venous blood (i.e. less 0₂ and more CO₂ containing blood) comes from the upper part of the body through the superior vena cava and from the lower part of the body through the inferior vena cava to the right atrium of the heart. The right atrium also receives reduced (venous) blood from the heart muscle through coronary sinus.

During atrial systole, the venous blood from the right atrium passes into the right ventricle by opening the tricuspid valve (atrioventricular valve) present at the right atrioventricular orifice.

After filling, the systole of the right ventricle expels the venous blood into the lungs by the pulmonary trunk (artery) through the right atrioventricular orifice. It is guarded by the semilunar valve.

After oxygenation, the venous blood converts into the arterial blood which contains more 0₂ and less CO₂. This blood then returns to the left atrium through four pulmonary veins (two arising from each lung).

From the left atrium, the blood passes into the left ventricle by opening the bicuspid valve (Mitre! valve) present at the left atrioventricular orifice.
During contraction of the ventricles, the oxygenated blood from the left ventricle flows into the large artery called the aorta by opening the aortic valve (semilunar valves) present at the left atrioventricular orifice.

Describe the structure of human heart and discuss about the mechanism of circulation.

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