Ch 26 Osmoregulation

Ch 26 Osmoregulation - Cha p te r 26 : Flu id , Ele ct ro...

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Chapter 26: Fluid, Electrolyte, and Acid-Base Balance I. Body Fluids A. Body Water Content 1. 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 since 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 1. There are two main fluid compartments of the body: the intracellular compartment (ICF) contains slightly less than two-thirds by volume; the remaining third is distributed in the extracellular fluid (ECF). 2. There are two subcompartments of the extracellular fluid: blood plasma and interstitial fluid. C. Composition of Body Fluids 1. 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. D. Fluid Movement Among Compartments 1. Anything that changes solute concentration in any compartment leads to net water flows. 2. Nearly protein-free plasma is forced out of the blood by hydrostatic pressure, and almost completely reabsorbed due to colloid osmotic pressure of plasma proteins. 3. Movement of water between the interstitial fluid and intracellular fluid involves substantial two-way osmotic flow that is equal in both directions. 4. Ion fluxes between the interstitial and intracellular compartments are restricted; but movement of nutrients, respiratory gases, and wastes typically occur in one direction. II. Water Balance and ECF Osmolality A. For the body to remain properly hydrated, water intake must equal water output. 1. Most water enters the body through ingested liquids and food, but is also produced by cellular metabolism. 2.
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Ch 26 Osmoregulation - Cha p te r 26 : Flu id , Ele ct ro...

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