The two superior atria are primarily the receiving chambers, they play a lighter role in the pumping activity of the heart.
Discharging Chambers
The two inferior, thick-walled ventricles are the discharging chambers, or actual pumps of the heart wherein they contract, blood is propelled out of the heart and into the circulation.
Tunica Intima
Lines the lumen, or interior, or the vessels, is a thin layer of endothelium resting on a basement membrane and decreases friction as blood flows through the vessel lumen.
Purkinje fibers
Pale-staining fibers, larger than the adjacent contractile muscle fibers, with sparse, peripheral myofibril and much glycogen.
Pericardium
The heart is enclosed in a double-walled sac called pericardium and is the outermost layer of the heart.
