The liquid contained in human and animal bodies, including water and dissolved substances, accounts for about 60-70% of the body weight.
Body fluid can be divided into two parts: intracellular fluid, which exists in cells and accounts for about 40 ~ 45% of body weight; Extracellular fluid existing outside cells accounts for about 20 ~ 25% of body weight.
Extracellular fluid can be divided into blood, interstitial fluid (interstitial fluid or intercellular fluid for short), lymph, cerebrospinal fluid and gastrointestinal secretions. The extracellular fluid of15 is plasma, which is a liquid existing in blood vessels, accounting for about 4-5% of the body weight, and the extracellular fluid of 4/5 is tissue fluid, which is a liquid existing in the interstitial space, accounting for about15-20% of the body weight. The volume of gastrointestinal secretions varies greatly, generally accounting for 1-3% of body weight. Tissue fluid and intracellular fluid are separated by cell membrane; Tissue fluid and blood are separated by blood vessel wall. Intracellular fluid, water in tissue fluid and blood, and all substances that can penetrate cell membrane and capillary wall can be exchanged with each other.
Human metabolism is a series of complex biophysical and biochemical reaction processes, which are mainly carried out in cells, and these processes are inseparable from water. The volume, distribution and electrolyte concentration of water in the body are all regulated by the wonderful human body, which makes the volume, electrolyte concentration, osmotic pressure and pH value of body fluid inside and outside the cell relatively stable in dynamic balance. This balance is a necessary condition for human cell metabolism. It may be destroyed by trauma, infection, improper treatment and bad living habits, which is beyond the adjustment ability of the human body. This can lead to a series of sub-health manifestations, and when it develops to a certain extent, it can become the main factor threatening life.
The fluid in human and animals can be divided into two parts: intracellular fluid and extracellular fluid. Human body fluids account for about 65% of body weight. Most of them exist in cells, called intracellular fluid, which is the basic component of protoplasm. A small part exists outside the cell, which is called extracellular fluid. Extracellular fluids of higher animals include plasma, lymph, cerebrospinal fluid and tissue fluid. Although they are separated from each other and have different components, they are interrelated, and plasma plays a connecting role among various fluids. Because blood circulates in the cardiovascular system, capillaries are all over the body, and its total area is estimated to be about 83 10 square meter. However, only a small part of capillaries in the body are usually open. But it is also enough for physical exchange. When blood flows through the digestive tract and lungs, it gets nutrients from the gastrointestinal tract and oxygen from the lungs. When it flows through the tissues and cells of the whole body, it transports nutrients and oxygen to the cells through the interstitial fluid to meet the needs of the cells. At the same time, the products of cell metabolism enter the blood, are transported to organs such as kidney, lung and skin through circulation, and are discharged from the body, so that the blood is constantly updated, which is one of the important conditions for maintaining the relative stability of the internal environment of the body.