Body fluids are generally understood to be water, which is found in various sections and parts of the human body and, depending on the section, is provided with additional substances dissolved in it, such as excretion products or electrolytes. A distinction is made between body fluids that circulate in different body circuits, such as blood or bile, and those that are located within different body cavities, such as the aqueous humor of the eye or gastric acid. The latter fluids are also subject to a certain circulation through consumption and new formation.
If we look at the distribution of body fluids one step smaller at the cellular level, we distinguish between fluids that are inside cells (intracellular), which form organs and body structures, and fluids outside the cells (extracellular). This is not a fixed system and, depending on the current situation and needs, fluctuations can occur, i.e. water can always flow out of and into the cell. This process is called diffusion. These systems are regulated by certain hormones, among other things. In the sections below, the most important body fluids are briefly introduced with their respective main functions.
Quantity, distribution, loss, absorption
In general, the human body consists of about 55-65% water, which, as already mentioned, is distributed throughout the body. There are, however, slight differences in this percentage, which, for example, decreases in the course of life. Children therefore have a higher percentage than adults.
Women have 5-10% less body water than men. 2/3 of the body water is inside the cells, 1/3 is outside of them. The human body loses an average of 2.5 l of water daily through sweating and excretions such as urine and stool.
As a rule of thumb, 30 ml of water per kilogram of body weight should be returned to the body through drinking every day. However, this requirement is increased if you sweat excessively during sports or at high temperatures. During a one-hour sporting activity, this requirement increases by half a liter. If there is too little fluid in the body, we speak of dehydration, and if there is too much fluid, we speak of hyperhydration.
