Chapter 14. Fluid, Electrolyte, and Acid-Base Balance
14.0 Introduction
Chapter Objectives
After studying this chapter, you will be able to:
- describe how antidiuretic hormone (ADH), aldosterone, and atrial natriuretic peptide (ANP) are important in maintaining body fluid balance;
- describe how sodium, potassium, calcium, and phosphate levels are regulated;
- state the most important chemical buffers in the extracellular fluid (ECF) and intracellular fluid (ICF);
- write the equation illustrating the carbonic acid-bicarbonate buffer system;
- describe the main ways in which the respiratory system and the kidneys maintain acid-base balance;
- define respiratory acidosis and alkalosis and metabolic acidosis and alkalosis; and
- solve arterial blood gas (ABG) problems to determine a person’s acid-base status.
Generally speaking, the regulation of body fluid balance involves controlling total body water content and extracellular fluid (ECF) osmolarity along with ECF volume. Maintaining these parameters within their homeostatic ranges involves several body systems working together. In the last chapter, the vital role of the urinary system in regulating electrolyte levels was discussed. In this chapter we will further investigate how the kidneys, endocrine system, and cardiovascular system work in concert to regulate body fluid balance. Specifically, we will discuss how the body maintains water balance, ECF osmolarity, ECF volume, and electrolyte balance. Although the maintenance of these parameters is discussed in separate sections in this chapter, their regulation is deeply intertwined, such as the following examples:
- maintaining ECF osmolarity requires that water balance in fluid compartments be maintained; and
- ECF osmolarity determines ECF volume and ECF volume determines blood pressure.
The importance of maintaining plasma pH between 7.35 and 7.45 was introduced in Chapter 2. Plasma pH maintenance, or acid-base balance, is achieved by the respiratory system and the kidneys, and these actions are described further in this chapter.
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