physiology-Distribution of fluids within the body

Distribution of fluids within the body 

Total Body Water

Right now, you are reading the text here and you probably thinking about this question (why would you!?)

What percentage of my body is water?

If you are fairly lean or fit person you are probably going to be 60% water. If you are lean young women you are going to be 50% water. if you’re maybe a slightly older man who’s maybe a little bit less lean then proportionately you’re going to contain less water. Where is this water though?

We can divide two or three main compartments, intracellular, extracellular and sometimes we count transcellular another compartment.

Intracellular fluid is approximately 40% of the total body weight. It is the total space within cells primarily defined as the cytoplasm of cells. In general, intracellular fluids are stable and do not readily adjust to rapid changes. This space is where much of chemical reactions occur, as such, it is important to maintain an appropriate osmolality.

The extracellular fluid comprises approximately 20% of total body weight and further subcategorizes as plasma at approximately 5% of body weight and interstitial space which is approximately 12% of body weight.

Transcellular fluid is the portion of total body water contained within the epithelial-lined spaces. It is the smallest component of extracellular fluid, which also includes interstitial fluid and plasma. It is often not calculated as a fraction of the extracellular fluid, but it is about 2.5% of the total body water. Examples of this fluid are cerebrospinal fluid, ocular fluid, joint fluid, and the pleural cavity that contains fluid that is only found in their respective epithelium-lined spaces. The function of transcellular fluid is mainly lubrication of these cavities, and sometimes electrolyte transport.

Figure 1. distribution of fluids

Intracellular fluid (ICF): approximately 60% of total of body water.

Extracellular fluid (ECF): approximately 40% of total body water.

Interstitial fluid (ISF): approximately 3/4 of the extracellular fluid.

Plasma volume (PV): approximately 1/4 of the extracellular fluid.