Describe the structure of heart of the man with the help of neat labeled diagram.

The heart is mesodermal in origin, situated in the mediastinum.
Pericardium :
* It is a protective layer with outer fibrous pericardium and the inner serous pericardium.
* The serous pericardium is double layered formed of an outer parietal layer and inner visceral layer with pericardial fluid.
* The wall of the heart consists of three layers,
* Outer epicardium * Middle myocardium
* Inner endocardium
Structure of the heart :
* Heart is divided into 4 chambers, two atria and two ventricles.
Atria :
* These are thin walled, blood receiving chambers.
* Right atrium is larger than the left atrium.
* These are separated internally by thin interatrial septum.
* Right atrium receives deoxygenated blood from different parts of body through two caval
veins, precaval vein and postcaval vein.
* The opening of pre-caval vein has no valve.
* The opening of coronary sinus into the right atrium is guarded by valve of Thebesius.
* Left atrium receives oxygenated blood from each lung through two pulmonary veins.
* The left and right atrioventricular apertures are guarded by bicuspid(mitral valve) and tricuspid valves respectively.
Ventricles :
* These are thick walled blood “pumping chambers” which are separated by an interventricular septum.
* Muscular ridges of inner surface are called columnae carneae.
* Some large and conical ridges called papillary muscles are connected to the tricuspid and bicuspid valves by chordae tendineae or heart strings.
Nodal tissue :
* Sino-atrial node(SAN) present in the right atrium near the opening of the superior vena cavae.
* Atrio-ventricular node(AVN) is seen in the lower left corner of the right atrium.
* AVN gives off AV bundle, which divides into bundle branches further divided into Purkinje fibres.
Aortic arches :
* There are two aortic arches in man.
* Pulmonary arch : It arises from the right ventricle.
* Systemic arch (left): It arises from the left ventricle.
* The openings of both arches are guarded by pulmonary and aortic valves.
* Ligamentum arteriosum : is present at the point of contact of the systemic and pulmonary arches.