Describe the structure of the heart of human with the help of neat labelled diagram.
Heart, the mesodermally derived organ, is situated in the thoracic cavity, in between the two lungs, slightly tilted to the left.
It is protected by a double-walled membranous bag, pericardium, enclosing the pericardial fluid.
Our heart has four chambers, two relatively small upper chambers called atria and two larger lower chambers called ventricles.
The atrium and the ventricle of the same side are also separated by a thick fibrous tissue called the atrioventricular septum. However, each of these septa is provided with an opening through which the two chambers of the same side are connected. The opening between the right atrium and the right ventricle is guarded by a valve formed of three muscular flaps or cusps, the tricuspid valve, whereas a bicuspid or mitral valve guards the opening between the left atrium and the left ventricle.
The openings of the right and the left ventricles into the pulmonary artery and the aorta respectively are provided with the semilunar valves.
The valves in the heart allow the flow of blood only in one direction, i.e., from the atria to the ventricles and from the ventricles to the pulmonary artery or aorta. These valves prevent any backward flow.
A patch of this tissue is present in the right upper corner of the right atrium called the sino-atrial node (SAN). Another mass of this tissue is seen in the lower left corner of the right atrium close to the atrioventricular septum called the atrioventricular node (AVN). The nodal musculature has the ability to generate action potentials without any external stimuli, i.e., it is autoexcitable.