Among the elements in human body, carbon, oxygen, nitrogen and hydrogen account for about 96%, accounting for an absolute majority in the composition table. In human body, elements mainly exist in two forms: water and carbonaceous organic matter.
At present, there are more than 60 known elements in human body. At present, it is considered that the essential elements for maintaining life are oxygen, carbon, hydrogen, nitrogen, calcium, phosphorus, potassium, sodium, chlorine, sulfur, magnesium, iron, silicon, zinc, copper, manganese, cobalt, iodine, molybdenum and *** 19. There is still doubt about the necessity of fluorine. In addition, the necessity of boron, aluminum, gold, silver, mercury and other elements is also questionable. Many people think that these elements enter the human body by accident and are not necessary for the human body.
According to the periodic table of elements, the constituent elements of human body are widely distributed from I to VIII. Most of the elements belong to 1 period to 4 period, and the atomic number is relatively small, so most of them are relatively light elements.
Except for carbon, oxygen, nitrogen and hydrogen, for other elements, calcium and phosphorus are abundant in bones, potassium is more in intracellular fluid, and sodium is more in extracellular fluid, that is, blood and tissue fluid. Sulfur is a component of protein, chlorine and magnesium are salts existing in body fluids, iron is a component of heme, copper is a component of enzyme, manganese is a component of coenzyme, iodine is contained in thyroxine, and cobalt is contained in vitamin B 12 (Table 2-2).
Table 2-2 Human Body Composition
element
Mass fraction/%
Mainly containing molecules
oxygen
65
Water, organic matter
carbon
18
Carbohydrate, lipid, protein, nucleic acid.
hydrogen
10
Carbohydrate, lipid, protein, water.
nitrogen (N)
three
Protein, nucleic acid.
calcium (Ca)
1.5
Bone inorganic matter
phosphorus (P)
1.0
Carbohydrate intermediates, nucleic acids, bone inorganic substances
sulphur
0.25
protein
potassium
0.2
intracellular fluid
natrium
0. 15
Extracellular fluid (plasma, tissue fluid)
chlorine
0. 15
extracellular fluid
magnesium
0.05
extracellular fluid
iron
0.006
hemoglobin
copper
0.0002
copper proteins
manganese
0.00003
cozymase
iodine
0.00004
thyroid hormone
cobalt
—
vitamin B2
Second, the main compounds contained in the human body
The classification forms of human compounds are generally as follows:
The proportion of various components in the human body varies with age, sex, nutritional status and individual differences, especially lipids. People with more lipids have less water. Most other ingredients are stable. Protein content is generally around 15% ~ 18% (Table 2-3).
Table 2-3 Main Compounds in Human Body
multiple
Content (percentage of body weight)/%
multiple
Content (percentage of body weight)/%
water
60~75
carbohydrate
& lt 1
protein
15~ 18
inorganic matter
2~6
oil
16~58
The composition of the human body varies with the parts, organs, tissues and cells of the human body. For example, the water content in blood is 77% ~ 8 1%, and only 2% in enamel; As far as protein is concerned, its content in gluten is 17% ~ 22%, but it is only 7% in serum.
1, water
The water content and its distribution in human body are directly related to age. Generally, the younger the age, the higher the water content and the more water distributed in the extracellular fluid (Table 2-4).
In addition, there is a certain relationship between the water content of the human body and the fat content in the body. Because adipose tissue contains little water, the water content in the fat body is generally less. In terms of the importance of water to life, thin people and fat people with the same weight will do more harm to fat people if they lose the same weight of water.
Table 2-4 Water Content and Distribution of Children and Adults in Different Age Groups (Weight Percentage)
Term newborn
1 year
2 ~ 14 years old
adult
Total body fluid
80
70
65
60
intracellular fluid
35
40
40
40
cell
External fluid
Intercellular fluid
40
25
20
15
blood plasma
five
five
five
five
2. Inorganic substances
In the chemical composition of a healthy person weighing 65㎏, the total amount of inorganic substances is about 4㎏, accounting for 6% of the whole body weight. In the distribution of these four "inorganic substances", the skeletal part accounts for more than 80%, and the muscular part accounts for about 10% (Table 2-5).
Table 2-5 4.0㎏ In vivo distribution of inorganic substances
Tissue site
Mass fraction/%
Tissue site
Mass fraction/%
skeleton
83. 1
brain
0.7
muscle
10.4
blood
0.7
skin
1.0
intestines
0.6
liver
0.8
lung
0.5
In addition, the inorganic components of intracellular fluid and extracellular fluid are also different. Among them, intracellular fluid mainly contains potassium ions, and extracellular fluid mainly contains sodium ions.
3. carbohydrates
Carbohydrates in the body mainly include glycogen and mucopolysaccharide. Glycogen is the main carbohydrate in human body and an important component to maintain normal blood sugar level, but its content is generally less than 1%.