Join us as we explore the crucial fluid environment within our bodies, beginning with the fact that approximately 60% of the human adult body is composed of fluid. We'll break down how this fluid is distributed: about two-thirds, or 28 liters in adults, is found inside cells (intracellular fluid or ICF), while the remaining one-third, about 14 liters, is located outside cells (extracellular fluid or ECF).

Discover why the extracellular fluid is often called the INTERNAL ENVIRONMENT of the body. We'll explain how it's the vital milieu containing the essential ions and nutrients that cells need to survive, function optimally, grow, and sustain life activities. This includes crucial components like oxygen, glucose, various ions, amino acids, and fatty acids.

We'll also highlight the important differences in composition between these fluid compartments. You'll learn that extracellular fluid is rich in sodium, chloride, and bicarbonate, but low in potassium, while intracellular fluid is rich in potassium, magnesium, and phosphate, and low in sodium and chloride.

Then, we'll shift our focus to dehydration, which is characterized by a reduction in the volume of extracellular fluid. Crucially, we'll delve into why children are significantly more susceptible to severe dehydration compared to adults.

We'll explain the key factors behind this vulnerability. In infants and children, the ratio of extracellular fluid to intracellular fluid is higher than in adults, although their absolute volume of ECF is smaller. Consequently, even a minor loss of extracellular fluid can quickly lead to dehydration in children. As a result of these factors, dehydration tends to develop more rapidly and is often more severe in children compared to adults.