atria and atrium of heart

 Heart contains four chamber-

Atrium

1. Right atria

2. Left atria

Ventricles

3. Right ventricles

4. Left ventricles

Heart divided into right and left side by septum.

Atria; Recieving chamber

Ventricle; Discharging chamber

Atria

(Opening present in right atrium)

1. Right atrium

Right upper chamber of Heart receives deoxygenated blood from superior and inferior venacava and coronary sinus, anterior cardiac veins and small cardiac vein, send down to right Ventricle (through tricuspid opening).

2. Left atrium

Left upper chamber of heart, receives oxygenated blood from left and right pulmonary vein (4), pump it to the left ventricle (through mitral valve or bicuspid valve).