The function of the sarcoplasmic reticulum is to store and release calcium ions in the body's muscle cells, according to the Dr. Evangelia Kranias Lab at the University of Cincinnati. The sarcoplasmic reticulum is the main organ through which calcium in the muscles is handled and regulated.
The role of the sarcoplasmic reticulum of smooth muscles may change as the body changes physiological states or experiences illness and disease, reports a study published by the National Center for Biotechnology Information. In addition to being a calcium storage mechanism, the sarcoplasmic reticulum was originally thought to be synthetic and a storage mechanism for contractile proteins. The National Institutes of Health study points out that researchers have expanded the explanation of the sarcoplasmic reticulum's functions to include homeostasis and contribution to signaling in other organelles such as the nucleus and mitochondria.
The sarcoplasmic reticulum is similar in structure to the endoplasmic reticulum, except for the assortment of proteins it contains, says Wikipedia. This one difference causes both organs to function quite differently in the body. The sarcoplasmic reticulum stores large amounts of calcium and then releases it when muscles become stimulated, but the endoplasmic reticulum mainly synthesizes and transports proteins to a cell system known as the Golgi apparatus.