The Cardiovascular System is sustained by the heart, a powerful hollow muscle which is the central pump of the body. It is pear-shaped, about the size of a fist, and weighs approximately 9 ounces. The entire structure is enclosed in a tough fibrous sac, the pericardium, containing a small amount of lubricating fluid which eliminates friction in this area as well as holding the heart in its position. The thick muscular wall of the heart, the myocardium, is responsible for the contractions the heart makes. The interior of the heart is lined with a thin smooth membrane, the endocardium as well as blood vessels called endothelium. The interior of the heart is divided into two separate cavities, auricle which receives blood and the ventrivcle which pumps out blood.
The image above is of the cardiovascular system.
Sources: Fishbein, Morris. The New Illustrated Medical and Health Encyclopedia.
New York: H. S. Stuttman, 1970. Print.
New York: H. S. Stuttman, 1970. Print.