Molecular clouds may collide with each other, or a nearby supernova explosion can be a trigger, sending shocked matter into the cloud at very high speeds. Alternatively, galactic collisions can trigger massive starbursts of star formation as the gas clouds in each galaxy are compressed and agitated by tidal forces.
Coordinated contractions of cardiac muscle cells in the heart propel blood out of the atria and ventricles to the blood vessels of the left/body/systemic and right/lungs/pulmonary circulatory systems.This complex mechanism illustrates systole of the heart.ardiac muscle cells, unlike most other tissues in the body, rely on an available blood and electrical supply to deliver oxygen and nutrients and remove waste products such as carbon dioxide. The coronary arteries help fulfill this function.
Heart muscle exhibits many structural and functional characteristics intermediate between those of skeletal and smooth muscle. Like skeletal muscle, cardiac muscle contractions are strong, and utilise a great deal of energy. Like some smooth muscle, cardiac muscle can contract without nervous stimulation (i.e. it is myogenic) and this enables the heart to be transplanted.