Body Fluid Compartments

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To repeat, the internal environment can be equated with the extracellular fluid. It was not stated earlier that extracellular fluid exists in two locations—surrounding cells and inside blood vessels. Approximately 80 percent of the extracellular fluid surrounds all the body's cells except the blood cells. Because it lies "between cells," this 80 percent of the extracellular


CHAPTER ONE A Framework for Human Physiology fluid is known as interstitial fluid. The remaining 20 percent of the extracellular fluid is the fluid portion of the blood, the plasma, in which the various blood cells are suspended.

As the blood (plasma plus suspended blood cells) flows through the smallest of blood vessels in all parts of the body, the plasma exchanges oxygen, nutrients, wastes, and other metabolic products with the interstitial fluid. Because of these exchanges, concentrations of dissolved substances are virtually identical in the plasma and interstitial fluid, except for protein concentration. With this major exception—higher protein concentration in plasma than in interstitial fluid—the entire extracellular fluid may be considered to have a homogeneous composition. In contrast, the composition of the extracellular fluid is very different from that of the intracellular fluid, the fluid inside the cells. (The actual differences will be presented in Chapter 6, Table 6-1.)

In essence, the fluids in the body are enclosed in "compartments." The volumes of the body-fluid compartments are summarized in Figure 1-3 in terms of water, since water is by far the major component of the fluids. Water accounts for about 60 percent of normal body weight. Two-thirds of this water (28 L in a typical normal 70-kg person) is intracellular fluid. The remaining one-third (14 L) is extracellular and as described above, 80 percent of this extracellular fluid is interstitial fluid (11 L) and 20 percent (3 L) is plasma.

Compartmentalization is an important general principle in physiology. (We shall see in Chapter 3 that the inside of cells is also divided into compartments.)

Compartmentalization is achieved by barriers between the compartments. The properties of the barriers determine which substances can move between contiguous compartments. These movements in turn account for the differences in composition of the different compartments. In the case of the body-fluid compartments, the intracellular fluid is separated from the extracellular fluid by membranes that surround the cells; the properties of these membranes and how they account for the profound differences between intracellular and extracellular fluid are described in Chapter 6. In contrast, the two components of extracellular fluid—the interstitial fluid and the blood plasma—are separated by the cellular wall of the smallest blood vessels, the capillaries. How this barrier normally keeps 80 percent of the extracellular fluid in the interstitial compartment and restricts proteins mainly to the plasma is described in Chapter 14.

This completes our introductory framework. With it in mind, the overall organization and approach of this book should easily be understood. Because the fundamental features of cell function are shared by virtually all cells and because these features constitute the foundation upon which specialization develops, we devote Part 1 of the book to an analysis of basic cell physiology.

Part 2 provides the principles and information required to bridge the gap between the functions of individual cells and the integrated systems of the body. Chapter 7 describes the basic characteristics of home-ostatic control systems and the required cellular communications. The other chapters of Part 2 deal with the

Total body water (TBW)

" Volume = 42 L, 60% body weight

Extracellular fluid (ECF)

(Internal environment) Volume = 14 L, 1/3 TBW

Intracellular fluid Volume = 28 L, 2/3 TBW

Interstitial fluid Volume = 11 L 80% of ECF

Plasma Volume = 3 L 20% of ECF

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  • Dolly
    Which barriers separate body fluids into different compartments?
    9 years ago
    What fluid compartment are capillaries in?
    9 years ago
  • Ayaan
    Is blood intracellular or extracellular fluid?
    9 years ago
  • debora
    What is the difference between intracellular and extracellular body fluids?
    9 years ago
  • barbara
    What are two fluid compartments of body and component parts?
    9 years ago
  • milo twofoot
    What represents about one third of all body fluid?
    9 years ago
  • Vincent
    What is the concentration of blood plasma and interstitial fluid in the intracellular membrane?
    9 years ago
  • joona
    Which of the following fluids are nearly identical except for protein content plasma?
    9 years ago
  • thomas
    What are the major difference between intracellular and extracellular fluids?
    9 years ago
  • Dean
    Why have different compositions of the fluid compartments?
    8 years ago
  • Primula
    What are the 2 components of extracellular fluid?
    8 years ago
  • rollo
    What are the two functional fluid compartments in the body?
    8 years ago
  • debra freed
    What 2 “barriers” separate the interstitial fluid, intracellular fluid & the blood plasma?
    8 years ago
  • amelia findlay
    What percentage is fluid portion?
    8 years ago
  • Thorsten
    What are 3 substances that can can move between the internal fluid compartments of the body?
    8 years ago
  • Fraser Davidson
    Which of these properties do interstitial and intracellular fluid?
    8 years ago
  • Anne
    Which barriers separate body fluids into different compartment?
    8 years ago
  • john
    Which of these properties do interstitial and intracellular fluid share?
    7 years ago
  • charlene franco
    Is blood the smallest fluid compartment in the body?
    7 years ago
  • belinda
    What is the blood component that links the external and internal fluid compartments?
    7 years ago
  • J
    What is the function of plasma sun siero in the body?
    7 years ago
  • christopher
    Which of these properties do interstitial and intracellular fluid share quizlet?
    4 years ago
  • prisca
    Which barriers seperate body fluids into different compartments?
    4 years ago
  • don
    Are intracellular fluid homogeneous?
    3 years ago

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