26: Fluid, Electrolyte, and Acid-Base Balance
List the factors that determine body water content and describe the effect of each factor.
Indicate the relative fluid volume and solute composition of the fluid compartments of the body.
Contrast the overall osmotic effects of electrolytes and nonelectrolytes.
Describe factors that determine fluid shifts in the body.
Water Balance and ECF Osmolality
List the routes by which water enters and leaves the body.
Describe feedback mechanisms that regulate water intake and hormonal controls of water output in urine.
Explain the importance of obligatory water losses.
Describe possible causes and consequences of dehydration, hypotonic hydration, and edema.
Indicate routes of electrolyte entry and loss from the body.
Describe the importance of ionic sodium in fluid and electrolyte balance of the body, and indicate its relationship to normal cardiovascular system functioning.
Describe mechanisms involved in regulating sodium balance, blood volume, and blood pressure.
Explain how potassium, calcium, and anion balances in plasma are regulated.
List important sources of acids in the body.
Name the three major chemical buffer systems of the body and describe how they resist pH changes.
Describe the influence of the respiratory system on acid-base balance.
Describe how the kidneys regulate hydrogen and bicarbonate ion concentrations in the blood.
Distinguish between acidosis and alkalosis resulting from respiratory and metabolic factors. Describe the importance of respiratory and renal compensations to acid-base balance.
Developmental Aspects of Fluid, Electrolyte, and Acid-Base Balance
Explain why infants and the aged are at greater risk for fluid and electrolyte imbalances than are young adults. Chapter Outline
Body Fluids (pp. 996–998; Figs. 26.1–26.3)
Body Water Content (p. 996)
Total body water is a function of age, body mass, and body fat. a.
Due to their low body fat and bone mass, infants are about 73% water. b.
The body water content of men is about 60%, but because women have relatively more body fat and less skeletal muscle than men, theirs is about 50%. 2.
Body water declines throughout life, ultimately comprising about 45% of total body mass in old age. B.
Fluid Compartments (p. 996; Fig. 26.1)
There are two main fluid compartments of the body: The intracellular compartment contains slightly less than two-thirds by volume; the remaining third is distributed in the extracellular fluid. 2.
There are two subcompartments of the extracellular fluid: blood plasma and interstitial fluid. C.
Composition of Body Fluids (pp. 996–998)
Nonelectrolytes include most organic molecules, do not dissociate in water, and carry no net electrical charge. 2.
Electrolytes dissociate in water to ions, and include inorganic salts, acids and bases, and some proteins. 3.
Electrolytes have greater osmotic power because they dissociate in water and contribute at least two particles to solution. 4.
The major cation in extracellular fluids is sodium, and the major anion is chloride; in intracellular fluid the major cation is potassium, and the major anion is phosphate. 5.
Electrolytes are the most abundant solutes in body fluids, but proteins and some nonelectrolytes account for 60–97% of dissolved solutes. D.
Fluid Movement Among Compartments (p. 998; Figs. 26.2–26.3) 1.
Anything that changes solute concentration in any compartment leads to net water flows. 2.
Substances must pass through both the plasma and interstitial fluid in order to reach the intracellular fluid, and exchanges between these compartments occur almost continuously, leading to compensatory shifts from one...
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