In humans, the heart is the primary motive force for driving the blood along the arterial vessels.
The heart consists of four separate chambers.
Two chambers function as a "right heart," and two function as a "left heart."
The muscular walls (myocardium) of the chambers apply force to the blood within and force the blood to move out of the chambers. (See Figure 10-3.)
The two chambers at the top of the heart are called atria (singular: atrium), while the two chambers at the bottom are called ventricles.
Label 1 Interatrial Septum
Down the middle of the heart, an interatrial septum separates the two atria.
Label 2 Interventricular Septum
Between the ventricles is the interventricular septum.
Label 3 The Atrium
The muscular walls of the atria tend to be relatively thin.
Attached to each atrium is an earlike appendage called an auricle. The auricles of the atria tend to have somewhat thicker walls.
Label 4 Left Ventricle
The left ventricle tends to be cylindrical in shape. It has a relatively thick wall.
Label 5 Right Ventricle
The right ventricle has a somewhat semilunar (half-moon) cross section, since it is wrapped around one side of the left ventricle.