Composition of fluids in the human body
In an adult, the total amount of fluid in the body is about 42L, which is 60% of the body weight. This rate also depends on the age, sex and physical condition of each person.
Total body fluid consists of two main parts: extracellular fluid and intracellular fluid. The extracellular fluid is made up of two components: the intercellular fluid and the vascular lumen.
There is another small amount of fluid, called "transcellular fluid". They are located in the synovial sac, peritoneal cavity, pericardium, as well as in cerebrospinal fluid; This fluid is considered a special form of extracellular fluid, although it sometimes migrates intracellularly or into the lumen. The amount of this fluid is about 1-2 L.
In an adult, the total amount of fluid in the body is about 42L, which is 60% of the body weight. This rate also depends on the age, sex and physical condition of each person. As a person ages, the amount of fluid in the body decreases. That's because the older you get, the more fat you have, so the amount of water will decrease.
In women, the amount of fat is more than in men, so the amount of water in the body will be low, accounting for about 50% of weight; In infants and young children, this amount is about 70-75% of body weight. Therefore, it is important to remember that the amount of water in the body varies by age, gender, and physical condition.
Figure. Regulates body fluids, including the main body compartments and the membranes that separate these compartments. The values are shown in an average adult male 70 kg.
Amount of intracellular fluid
The human body has 100 trillion cells, containing 28 L of the total 42 L of body fluids, this amount of fluid is called intracellular fluid, which accounts for an average of 40% of total body weight.
The amount of fluid in each cell is composed of many components, but the concentration of substances in each cell is exactly the same. Not only that, the concentration of substances in the cell is the same between different species, from unicellular to human. Therefore, the amount of fluid in all cells is considered to be one and the same.
Amount of extracellular fluid
All extracellular fluid is called extracellular fluid. This amount of fluid accounts for 20% of body weight, the amount is about 14L. The two main components of extracellular fluid are cytoplasmic fluid (accounting for ¾ of the amount, about 11 L) and plasma (accounting for ¼ , about 3 L).
Plasma is the amount of fluid in the blood but not in the cells, it exchanges continuously with the intercellular fluid through pores in the capillaries. These pores are highly permeable to most extracellular solutes except proteins. It is through this exchange that the concentrations of substances in the plasma and intercellular spaces are similar, except for proteins, which are highly concentrated in the plasma.
Blood cells include both extracellular fluid (plasma) and intracellular fluid (in blood cells). However, blood is considered as a very separate fluid component, contained in the circulatory system, which plays an extremely important role in maintaining hemodynamics.
The average amount of blood accounts for about 7% of body weight, about 5L, of which plasma accounts for 60%, the remaining 40% in blood cells. However, this amount also depends on age, gender and many other factors.
Hematocrit: Hematocrit is the fraction of red blood cells, determined by centrifugation of blood in a tube until the red blood cells settle. Because the blood cells cannot settle to the bottom of the tube when centrifuged because 3 to 4% of the cells are still mixed in the plasma, the measured hematocrit is only 96% of the actual hematocrit.
In men, the hematocrit is about 0.4; while in women it is 0.36. In patients with acute anaemia, the hematocrit can be reduced to 0.1, the lowest limit for sustaining life. In contrast, in people with abnormally increased red blood cell production, such as in polycythemia vera, the hematocrit can be as high as 0.65.