Human molecular formula
The position of the element calcium in the average human molecular formula is as follows:
Calcium is used in the development and maintenance of bone structure and development. Functions in the clotting process, nerve transmission, muscle stimulation, parathyroid hormone function, and metabolism of vitamin D, etc. 
The following are related quotes:
“Why should a group of simple, stable compounds of carbon, hydrogen, oxygen and nitrogen struggle for billions of years to organize themselves into a professor of chemistry? What's the motive? If we leave a chemistry professor out on a rock in the sun long enough the forces of nature will convert him into simple compounds of carbon, oxygen, hydrogen and nitrogen, calcium, phosphorus, and small amounts of other minerals. It's a one-way reaction.”— Robert Pirsig (1991), Lila: An Inquiry into Morals 
1. Thims, Libb. (2008). The Human Molecule (pg. 14) (issuu) (preview) (Google Books) (docstoc). LuLu.
2. Pirsig, Robert M. (1991). Lila: An Inquiry into Morals (excerpt, pg. 140; chemistry, 11+ pgs). Random House.
● Calcium – Wikipedia.