HEART

Human circulatory system

Human circulatory system also called blood vascular system. It consist of a muscular chambered heart, a network of closed branching blood vessels and blood.

HEART

Heart is mesodermally derived organ. It is situated in the thorasic cavity, in between the two lungs, slightly tilted to the left. Heart has the size of a clenched fist. It is protected by a double walled membranous bag, pericardium, enclosing the pericardial fluid. Pericardium is devided into outer epicardium, middle mesocardium, inner endocardium. 

Human heart has four chambers, two relatively small upper chamber called atria and two larger lower chamber called ventricles. 

A thin muscular wall called the inter-atrial septum separate the right and left atria, whereas a thick walled the inter ventricular septum separate the left and the right ventricles.

Atrium and the ventricle of the same side are also separated by a thick fibrous tissue called the Atrio ventricular septum. 

These septum has opening through which two chambers of same side are connected.

The opening between right atrium and right ventricle is guarded by a valve formed of three muscular flap or cusps called tricuspid valve. Whereas bicuspid or mitral valve guard the opening between the left atrium and left ventricle.

Right ventricle open into the pulmonary artery and left ventricle open into aorta. These opening is guarded by semilunar valves. 

Entire heart is made up of cardiac muscles. The wall of ventricle are much thicker than that of the atria. Thickest wall is found in left ventricle.