Heart Chamber - Atria Structure

Atria Structure

The right atrium contains the sinoatrial node which sends an impulse throughout the heart causing the cardiac muscle of the atrium to contract in a coordinated, wave-like manner. Since the atria are thin-walled and much less muscular than the ventricles, they are able to easily expand with the addition of blood. The forces of contraction are much weaker within the atria as a result. The contraction is strong enough, however to force 1/4 of the total blood volume entering into the ventricles. The rest of the blood enters the atria passively.

Read more about this topic:  Heart Chamber

Famous quotes containing the word structure:

    ... the structure of a page of good prose is, analyzed logically, not something frozen but the vibrating of a bridge, which changes with every step one takes on it.
    Robert Musil (1880–1942)