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After studying this chapter, you should be able to:

  • Define units used in measuring physiologic properties.

  • Define pH and buffering.

  • Understand electrolytes and define diffusion, osmosis, and tonicity.

  • Define and explain the significance of resting membrane potential.

  • Understand in general terms the basic building blocks of the cell: nucleotides, amino acids, carbohydrates, and fatty acids.

  • Understand higher-order structures of the basic building blocks: DNA, RNA, proteins, and lipids.

  • Understand the basic contributions of the basic building blocks to cell structure, function, and energy balance.


In humans and other vertebrate animals, specialized cell groups form into organs and include a gastrointestinal system to digest and absorb food; a respiratory system to take up O2 and eliminate CO2; a urinary system to remove wastes; a cardiovascular system to distribute nutrients, O2, and the products of metabolism; a reproductive system to perpetuate the species; and nervous and endocrine systems to coordinate and integrate the functions of the other systems. While this book is concerned with the way these systems function and the way each contributes to the functions of the body as a whole, this first chapter focuses on a review of basic biophysical and biochemical principles and the introduction of the molecular building blocks that contribute to cellular physiology.



The cells that make up the bodies of all, but the simplest multicellular animals are exposed to extracellular fluid (ECF) enclosed within the integument of the animal. Cells take up O2 and nutrients from this fluid, and they discharge metabolic waste products into it. The composition of ECF closely resembles that of the primordial oceans in which, presumably, all life originated.

In animals with a closed vascular system, the ECF is divided into the interstitial fluid, the circulating blood plasma, and the lymph fluid that bridges these two domains. The plasma and the cellular elements of the blood fill the vascular system, and together they constitute the total blood volume. The interstitial fluid is that part of the ECF that is outside the vascular and lymph systems, bathing the cells. About one-third of the total body water is extracellular; the remaining two-thirds is intracellular (intracellular fluid). In the average young adult male, 18% of the body weight is protein and related substances, 7% is mineral, and 15% is fat. The remaining 60% is water. The distribution of this water is shown in Figure 1–1A. Flow between these compartments is tightly regulated.


Organization of body fluids and electrolytes into compartments. (A) Body fluids can be divided into intracellular and extracellular fluid compartments (ICF and ECF, respectively). Their contribution to percentage body weight (based on a healthy young adult male; slight variations exist with age and gender) emphasizes the dominance of fluid ...

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