13.4: Fluid Compartments in the Body
- Page ID
- 126856
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)The human body is organized into distinct fluid compartments, each characterized by its own unique properties and functions. These compartments are separated by physical barriers, maintaining the integrity and segregation of the fluids.
Intracellular Fluid (ICF)
The ICF constitutes the fluid enclosed within cell membranes, existing within the cellular boundaries (Figure 2). It represents the primary component of the cytosol or cytoplasm. Approximately 60 percent of the body's total water content is allocated to the ICF. In an average-sized adult male, the ICF accounts for around 25 liters (equivalent to seven gallons) of fluid (Table 2). The volume of ICF remains relatively stable due to precise regulatory mechanisms. Maintaining the ICF within a balanced range is vital, as an imbalance may lead to cellular dehydration or overhydration, impacting cellular activities or causing hemolysis.
Figure 2 | Fluid Compartments in the Human Body |4 This diagram illustrates the distribution of body fluids in different compartments. The image illustrates the three major fluid compartments in the body: Intracellular Fluid (ICF), which is contained within the cells (beige-colored structures with purple nuclei); Interstitial Fluid (IF), which surrounds the cells in the extracellular space (blue background); and Plasma, the fluid component of blood within the blood vessel (red structure). These compartments play a crucial role in maintaining fluid balance and homeostasis in the body.
Extracellular Fluid (ECF)
The ECF encompasses the remaining one-third of the body's total water content. Around 20 percent of the ECF is represented by plasma, which plays a vital role in transporting various substances, including blood cells, proteins, electrolytes, nutrients, gasses, and waste products throughout the body. Interstitial fluid (IF) or tissue fluid represents a significant portion of the ECF. It is the fluid surrounding cells and serves as a medium for the exchange of gasses, nutrients, and waste products between the bloodstream and cells (Figure 2). The passage of materials between the IF and cells is regulated by selectively permeable cell membranes. Additionally, the ECF contains small amounts of other fluids, approximately 1 to 2 percent of body weight. These fluids are located in body cavities, including secretions of the gastrointestinal tract, urine, cerebrospinal fluid, and synovial fluid.
| Total Body Water (100%, 42 L) | ||
|---|---|---|
| Intracellular Fluid (ICF; 67%; 28L) | Extracellular Fluid (ECF; 33%; 14L) | |
| Interstitial Fluid (IF; 80% of ECF); 11L) | Plasma (20% of ECF); 3L | |
ECF acts as an intermediary between the body's internal and external environments, serving as a critical buffer zone. To maintain the standard composition of the ECF, numerous physiological mechanisms are in place. Whenever there is a deviation in the ECF composition from its normal state, compensatory mechanisms are triggered to restore equilibrium. For instance, a surge in blood glucose levels post-meal stimulates the release of insulin, aiding in the regulation of blood glucose levels by enhancing the uptake of glucose by the cells, thereby returning levels to their standard range.5