This article is about the chemical composition of the human body. For the body's content of fat, bone, and muscle, see body composition.

The human body's chemical composition consists of a variety of elements and compounds. By mass, human cells consist of 65–90% water (H₂O), and a significant portion is composed of carbon-containing organic molecules. Oxygen therefore contributes a majority of a human body's mass, followed by carbon. 99% of the mass of the human body is made up of the six elements oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus.

Contents 1 Elemental composition 2 Chemicals 3 Materials and tissues 4 Symbionts 5 See also 6 References

[edit] Elemental composition

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	3.8g in men, 2.3g in women
Cobalt, Copper, Zinc, Iodine	< 0.05 each
Selenium, Fluorine	< 0.01 each

(from Chang, Raymond (2007). Chemistry, Ninth Edition. McGraw-Hill. pp. p. 52. ISBN 0-07-110595-6. )^[1]

Other elements necessary for human life (see dietary mineral) are:

• manganese
• molybdenum
• nickel

A small amount of chromium is necessary for health.

Boron has been found necessary for optimal health in rats, so presumably it plays a role in humans as well.

The elements needed for life are relatively common in the Earth's crust, and conversely most of the common elements are necessary for life. An exception is aluminium, which is the third most common element in the Earth's crust (after oxygen and silicon), but seems to serve no function in living cells. Rather, it is harmful.

Besides these elements that are necessary for life, our bodies contain trace quantities of most other elements, including some that are harmful, such as mercury, cadmium, and lead.

[edit] Chemicals

The composition can also be expressed in terms of chemicals, such as:

• water
• proteins--including those of hair, connective tissue, etc.
• fats (or lipids)
• apatite in bones
• carbohydrates such as glycogen and glucose
• DNA
• dissolved inorganic ions such as sodium, potassium, chloride, bicarbonate, phosphate
• gases such as oxygen, carbon dioxide, nitrogen oxide, hydrogen, carbon monoxide, methanethiol. These may be dissolved or present in the gases in the lungs or intestines. Ethane and pentane are produced by oxygen free radicals.^[2]
• Many other small molecules, such as amino acids, fatty acids, nucleobases, nucleosides, nucleotides, vitamins, cofactors, hydrogen peroxide, and waste products like indole and skatole (in the intestinal contents).
• Free radicals such as superoxide, hydroxyl, and hydroperoxyl.

[edit] Materials and tissues

Body composition can also be expressed in terms of various types of material, such as:

• muscle
• fat
• bone and teeth
• brain and nerves
• connective tissue
• blood -- 7% of body weight. See List of human blood components.
• lymph
• contents of digestive tract, including intestinal gas
• urine
• air in lungs

[edit] Symbionts

There are many species of bacteria and other microorganisms that live on or inside the healthy human body. In fact, 90% of the cells in (or on) a human body are microbes, by number (much less by mass or volume).^[3] Some of these symbionts are necessary for our health. Those that neither help nor harm us are called commensal organisms. Besides these, there are harmful parasites and pathogens.

[edit] See also

• Hydrostatic weighing

[edit] References

1. ^ Distribution of elements in the human body (by weight) Retrieved on 2007-12-06
2. ^ Douglas Fox, "The speed of life", New Scientist, No 2419, 1 November 2003.
3. ^ Glausiusz, Josie. "Your Body Is a Planet". http://discovermagazine.com/2007/jun/your-body-is-a-planet. Retrieved 2007-09-16.