sodium (Na +), potassium (K +), and chloride (Cl –) ions, solute molecules e.g. The solvent is water, the solutes are numerous and include electrolytes e.g. Fluid within the human body is complex as it is both a solution as well as a mixture at the same time.Left undisturbed the sand would easily separate from the water and sink to the bottom, whereas the salt remains dissolved. However the water and the sand are not chemically combined and clearly exist as separate substances, i.e. At the shore the sea water disturbs the sand and some of the sand becomes mixed with the water. The two have undergone a reaction and combined in one new substance. The sea water is a solution as it is water (solvent) with salt (solute) dissolved in it. To illustrate this consider the sea and the beach. It is possible to have a fluid which is both a solution and also a mixture.
In order to fully understand the distribution and movement of water within the body there are some definitions, principles, and concepts that must first be understood: Solvents, solutes, and solutions Relations of the body fluid compartments. The final 1.5L comprises the transcellular fluid which is made up of intraocular fluid, cerebrospinal fluid (CSF), urine in the bladder, and fluid within the lumen of the bowelįigure 1.3.5L exists as blood plasma in blood vessels and is termed intravascular fluid.10L (approximately 2/3) exists in the spaces between cells and is termed interstitial fluid (ISF).The extracellular fluid is divided into several other compartments (Figure 1) The remaining one-third (15L) of TBW is outside the cells or “extracellular fluid” (ECF). The largest fluid ‘compartment’ which accounts for two-thirds (30L) of TBW is within the cells of the body and is called intracellular fluid (ICF). The compartments are separated from each other by membranes that regulate flow of water between each compartment and thereby control the amount of water which can exist in each of the compartments. Total body water is distributed throughout the body, and can be thought of as being in different ‘compartments’ or ‘spaces’. To simplify matters, all subsequent calculations will be based on this ‘ideal’ person with a total body water of 45 litres. Total body water (TBW) accounts for 60% of an adult male’s total body weight a normally hydrated 75 kilogram man will consist of approximately 45 litres of water. The amount of water in the body varies with a patient’s age, weight, and sex (Table 1).
HOW MUCH FLUID IS THERE IN THE BODY, AND HOW IS IT DISTRIBUTED?