Chemical Composition of the Human Body

Chemical Composition of the Human Body Many of the elements found throughout nature are also found within the body. This is the chemical composition of the average adult human body in terms of elements and also compounds. Major Classes of Compounds in the Human Body Most of the elements are found within compounds. Water and minerals are inorganic compounds. Organic compounds include fat, protein, carbohydrates, and nucleic acids. Water:  Water is the most abundant chemical compound in living human cells, accounting for 65 percent to 90 percent  of each cell. Its also present between cells. For example, blood and cerebrospinal fluid are mostly water.Fat: The percentage of fat varies from person to person, but even an obese person has more water than fat.Protein: In a lean male, the percentages of protein and water are comparable. Its about 16 percent  by mass. Muscles, including the heart, contain a lot of muscle. Hair and fingernails are protein. Skin contains a large amount of protein, too.Minerals: Minerals account for about 6 percent  of the body. They include salts and metals. Common minerals include sodium, chlorine, calcium, potassium, and iron.Carbohydrates: Although humans use the sugar glucose as an energy source, there isnt that much of it free in the bloodstream at any given time. Sugar and other carbohydrates only account for about 1% of body mass. Elements in the Human Body Six elements  account for 99%  of the mass of the human body. The acronym CHNOPS may be used to help remember the six key chemical elements that are used in biological molecules. C is carbon, H is hydrogen, N is nitrogen, O is oxygen, P is phosphorus, and S is sulfur. While the acronym is  a good way to remember the identities of the elements, it doesnt reflect their abundance. Oxygen is the most abundant element in the human body accounting for approximately 65% of a persons mass. Each water molecule consists of two hydrogen atoms bonded to one oxygen atom, but the mass of each oxygen atom is much higher than the combined mass of the hydrogen. In addition to being a component of water, oxygen is essential for cellular respiration.Carbon is contained in all organic compounds, which is why carbon is the second most abundant element in the body, accounting for about 18% of body mass. Carbon is found in proteins, carbohydrates, lipids, and nucleic acids. Its also found in carbon dioxide.Hydrogen atoms are the most numerous type of atom in a human, but because they are so light, they only make up around 10% of the  mass. Hydrogen is in water, plus its an important electron carrier.Nitrogen is about 3.3% of body mass. Its found in proteins and nucleic acids.Calcium accounts for 1.5% of body mass. Its used to build bones and teeth, plus its important for muscle contraction. Phosphorus is about 1% of body mass. This element is found in nucleic acids. Breaking bonds connecting phosphate molecules is a major component of energy transfer.Potassium is around 0.2-0.4% of the mass of a person. Its used in nerve conduction. Potassium is a key cation or positively-charged ion in the body.Sulfur is found in some amino acids and proteins. Its about 0.2-0.3% of body mass.Sodium, like potassium, is a positively-charged ion. Its about 0.1-0.2% of body mass. Sodium helps regulate the electrolyte balance in the body and maintain homeostasis with respect to the volume of water in the blood and cells.Although aluminum and silicon are abundant in the earths crust, they are found in trace amounts in the human body.Other trace elements include metals, which are often cofactors for enzymes. Trace elements include iron, cobalt, zinc, iodine, selenium, and flourine. Element Percent by Mass Oxygen 65 Carbon 18 Hydrogen 10 Nitrogen 3 Calcium 1.5 Phosphorus 1.2 Potassium 0.2 Sulfur 0.2 Chlorine 0.2 Sodium 0.1 Magnesium 0.05 Iron, Cobalt, Copper, Zinc, Iodine trace Selenium, Fluorine minute amounts Sources Anke M. (1986). Arsenic. In: Mertz W. ed., Trace elements in human and Animal Nutrition, 5th ed. Orlando, FL: Academic Press. pp. 347-372.Chang, Raymond (2007). Chemistry, Ninth Edition. McGraw-Hill. pp. 52.Emsley, John (2011). Natures Building Blocks: An A-Z Guide to the Elements. OUP Oxford. p. 83. ISBN 978-0-19-960563-7.Subcommittee on the Tenth Edition of the Recommended Dietary Allowances, Food and Nutrition Board; Commission on Life Sciences, National Research Council (February 1989). Recommended Dietary Allowances: 10th Edition. National Academies Press. ISBN 978-0-309-04633-6.Zumdahl, Steven S. and Susan A. (2000). Chemistry, Fifth Edition. Houghton Mifflin Company. p. 894. ISBN 0-395-98581-1.