The structure of human body

The human body structure can be divided into five levels. 1. Atomic level: At the atomic level, there are more than 130 known atoms, among which there are more than 60 elements in human body, mainly oxygen, hydrogen, carbon, nitrogen, calcium and phosphorus, among which the oxygen content is about 65%, carbon is about 18%, and hydrogen is about 10%. Second, the molecular level: At the molecular level, the human body is composed of protein, lipids, carbohydrates, water and minerals; The third is the cellular level: at the cellular level, the human body is composed of cells, extracellular fluid and extracellular solids. Cells are the main components that work in the body. Cells are usually divided into muscle cells, epithelial cells, nerve cells and other types according to their existing tissues. The fourth is the organizational level: at the organizational level, the human body is composed of tissues, organs and systems, so that the weight is equal to the sum of adipose tissue, skeletal muscle, bone, blood and other internal organs. Adipose tissue, including fat cells, blood vessels and some supporting structural components, is the main place to store fat. There are more than 400 skeletal muscles, the proportion of which varies with gender and age. The total blood volume of normal people accounts for about 8% of body weight; Five, the overall level: the composition of all levels of the human body is a dynamic process. For a person, in various periods such as fetus, baby, infant, adolescence, adulthood, old age and so on. Body composition will show certain changes, and certain changes will also occur under the conditions of disease and stress. But usually, in a certain period of time, such as months or years, the composition of the human body is relatively stable at all levels, that is to say, there is a stable quantitative relationship between various components.