Calcium has extreme biological importance in the body. In addition to its role in salivary gland ion transport and it plays a role in calcium and phosphate metabolism. Muscle contraction, nerve impulse transmission, membrane stability, blood clotting, and being an intracellular messenger summarize all of its important biological roles what remains to be addressed?
Calcium also plays a role in the endocrine and exocrine secretory functions of cells. i.e. an increase in the intracellular calcium concentration results from its release from the RER. This is done via Ach binding to it's receptor and activating DAG and IP3 through Phospholipase C.