Responsibilities of the cardiovascular system
The cardiovascular system is responsible for the movement and circulation of blood throughout the body of an organism. This is extremely important because blood contains oxygen and nutrients that are essential to life. Though size and shape may differ, most organisms use some form of heart or pumping device to propel blood throughout their body. Humans and birds have a four chamber heart (2 atria and 2 ventricles), which is the most efficient method of transporting nutrients and oxygenated blood. Amphibians and reptiles have a three chambered heart (2 atria and 1 ventricle), while fish have the smallest form of actual heart with only 1 atrium and 1 ventricle. The function of the atrium is to receive blood from the body of the organism and oxygenate it. When the blood is once again oxygenated, the ventricle pumps it out to the rest of the organism's body. Though all organisms have a heart-like feature, not all species have a traditional heart that has atria and ventricles. For some species such as insects or worms, there are pumping chambers that act as "hearts," integrated into the circulatory system.