Blood, Electrolytes, and Intravenous Infusions

2-4. CATEGORIES OF FLUIDS

Body water is divided into two primary types--intracellular fluid (ICF) and extracellular fluid (ECF). The intracellular is fluid that is contained within the body's cells. The fluid within the cells makes up about 2/3 of a person's total body water and accounts for about 50 percent of the person's body weight. The extracellular fluid is located in the body tissues, bones, and the body's vascular systems (blood and lymph). The fluids discussed thus far can be depicted as shown in figure 2-1.

a. The intracellular fluid functions in three ways. It transports food within the cells. It brings waste products from the cells so that they can be picked up and excreted from the body. This fluid also maintains the integrity (shape and size) of the cell.

b. The second type of body fluid is the extracellular fluid. The intracellular fluid is located outside the body cells. The extracellular fluid (ECF) comprises approximately one-third of the water contained in the body, and it accounts for approximately 15 percent of a person's body weight. The extracellular fluid has several

functions. It carries nutrients and oxygen to the cells and waste materials from the cells. It serves to bathe the cells in order to keep the cells moist. Two divisions or types of extracellular fluid are interstitial fluid and intravascular fluid. The interstitial fluid surrounds cells and it serves as a transporting medium to carry materials to and from cells. Approximately three fourths of the extracellular fluid is contained in the interstitial fluid. Interstitial fluid accounts for approximately 11 percent of a person's body weight. The second division of the extracellular fluid is the intravascular fluid (one-fourth of the extracellular fluid). The intravascular fluid is found in the body's circulatory systems. It accounts for approximately four percent of a person's body weight (see figure 2-2).

c. Body water diffuses throughout the body without recognizing anatomic boundaries. For example, water passes constantly across the tissue surface of the capillaries. If we could label all the water molecules by the function they were serving at a particular moment (interstitial, intravascular, and so forth), within another minute about half of them would be in another location or serving another function. There is an especially constant circulation of water (and the substance dissolved in it) between the fluids surrounding the cells and the blood.

Figure 2-2. Extracellular fluid distribution.