Wiki lists about 60 elements that compose the human body although it is probable that all 88 elements detectable in most soils might be found in the body, some purely as 'contaminants'. So, to answer the first part of your question, about 88 elements might be found in an average human body. Of these, about 24 to 25 actually play a key role in life and maintaining health.
The table in the wiki article lists all the elements, their mass in an average body and their function.http://en.wikipedia.org/wiki/Composition_of_the_human_body
99% of the human body, however, is composed of just 6 elements, oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus with oxygen being the most abundant at 65% by weight followed at a long second by carbon at 18%.http://chemistry.about.com/cs/howthingswork/f/blbodyelements.htm
Some of the most trace elements in the body are absolutely vital to health by acting as co-enzymes and co-factors in the numerous biochemical reactions that take place 24 hours a day, 365 days a year.Minerals and cofactors
Further information: Metal Ions in Life Sciences, Metal metabolism, and bioinorganic chemistry
Inorganic elements play critical roles in metabolism; some are abundant (e.g. sodium and potassium) while others function at minute concentrations. About 99% of a mammal's mass is made up of the elements carbon, nitrogen, calcium, sodium, chlorine, potassium, hydrogen, phosphorus, oxygen and sulfur. Organic compounds (proteins, lipids and carbohydrates) contain the majority of the carbon and nitrogen; most of the oxygen and hydrogen is present as water.
The abundant inorganic elements act as ionic electrolytes. The most important ions are sodium, potassium, calcium, magnesium, chloride, phosphate and the organic ion bicarbonate. The maintenance of precise gradients across cell membranes maintains osmotic pressure and pH. Ions are also critical for nerve and muscle function, as action potentials in these tissues are produced by the exchange of electrolytes between the extracellular fluid and the cytosol. Electrolytes enter and leave cells through proteins in the cell membrane called ion channels. For example, muscle contraction depends upon the movement of calcium, sodium and potassium through ion channels in the cell membrane and T-tubules.
Transition metals are usually present as trace elements in organisms, with zinc and iron being most abundant. These metals are used in some proteins as cofactors and are essential for the activity of enzymes such as catalase and oxygen-carrier proteins such as hemoglobin. Metal cofactors are bound tightly to specific sites in proteins; although enzyme cofactors can be modified during catalysis, they always return to their original state by the end of the reaction catalyzed. Metal micronutrients are taken up into organisms by specific transporters and bind to storage proteins such as ferritin or metallothionein when not being used.http://en.wikipedia.org/wiki/Metabolism#Minerals_and_cofactors
An alternative view is that we are all made of stardust!:The solar system, including the life upon planet Earth, is thought to be made of this star debris. Thus has arisen the poetic generalization that we are all “made of stardust” or star debris and are therefore “one with the universe.http://www.christiananswers.net/q-eden/made-of-stardust.html