Twenty-six different chemical element normally are present in your body. Just four elements, called the major elements, constitute about 96% of the body'd mass: oxygen, carbon hydrogen, and nitrogen. Eight others, the lesser elrments, contribute 3.8% to the body's mass: calcium, phosphorus (P), potassium (K), sulfur (S), sodium, chlorine (Cl), magnesium (Mg), and iron (Fe). An additional 14 elements the trace elements are present in tiny amounts. Together, they account for the remaining 0.2% of the body's mass. Several trace elements , iodine is needed to make thyroid hormones. The functions of some trace elements are unknown. Table 2.1 lists the main chemical elements of the human body.