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CURRENT Diagnosis & Treatment: Pediatrics, 20e
Chapter 44. Fluid, Electrolyte, & Acid-Base Disorders & Therapy
Sections: Regulation of Body Fluids, Electrolytes, & Tonicity, Acid-Base Balance, Fluid & Electrolyte Management, Dehydration, Hyponatremia, Hypernatremia, Potassium Disorders, Acid-Base Disturbances, Metabolic Acidosis, Metabolic Alkalosis, Respiratory Acidosis, Respiratory Alkalosis, References.
Excerpt:"Total body water (TBW) constitutes 50–75% of the total body mass, depending on age, sex, and fat content. After an initial postnatal diuresis, the TBW slowly decreases to the adult range near puberty (Figure 44–1). TBW is divided into the intracellular and extracellular spaces. Intracellular fluid (ICF) accounts for two-thirds of the TBW and extracellular fluid (ECF), for one-third. The ECF is further compartmentalized into plasma (intravascular) volume and interstitial fluid (ISF).In the kidney, ADH increases water reabsorption in the cortical and medullary collecting ducts, leading to formation of concentrated urine. In the absence of ADH, dilute urine is produced. Under normal conditions, ADH secretion is regulated by the tonicity of body fluids rather than the fluid volume and becomes detectable at a plasma osmolality of 280 mOsm/kg or greater. However, tonicity may be sacrificed to preserve ECF volume, as in the case of hyponatremic dehydration, wherein ADH secretion and renal water retention are maximal...."
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