CHAP27_2402 - C h a p t e r 2 7 1 BIOLOGY 2402 Anatomy and...

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Unformatted text preview: C h a p t e r 2 7 1 BIOLOGY 2402 Anatomy and Physiology Lecture Chapter 27 FLUID, ELECTROLYTES, AND ACID-BASE HOMEOSTASIS C h a p t e r 2 7 2 FLUID, ELECTROLYTES, AND ACID-BASE HOMEOSTAIS Body fluid refers to the body water and its dissolved substances. Fluid portion averages 55-60% of total body weight in lean adults. FLUID COMPARTMENTS AND FLUID BALANCE a) Intracellular Fluid (ICF)- body fluid within cells; (ie. 2/3 of body fluid). b) Extracellular Fluid (ECF)- includes all other body fluids outside the cells (ie 1/3 of body fluid). (1) Interstitial fluid , about 80% of the ECF, is found in the microscopic spaces between tissue cells. (2) Blood plasma , about 20% of ECF, is the liquid portion of blood within blood vessels. Selectively permeable membranes separate body fluids into distict compartments. Fluids exist in compartments, but are in constant motion from one compartment to another; In the healthy individual, the volume of fluid in each compartment remains relatively stable- another example of homeostasis. Fluid balance means that the various body compartments contain the required amount of water. Osmosis is the primary way in which water moves in and out of body compartments. C h a p t e r 2 7 3 The concentration of solutes in the fluids is therefore a major determinant of fluid balance. Electrolytes (compounds that dissociate into ions) are the most solutes in body fluids. Fluid balance, then, means water balance, but it also implies electrolyte balance. The two are inseparable. Body Water Water is the largest single constituent of the body; about 45-75% of the total body weight. Varies from person to person, sex, and age. Water proportion decreases with age. An infant has the highest amount of water per body weight - 75% of body weight. Normal adult male averages about 60% body weight. Normal adult female averages about 55% body weight. (Lose water due to more subcutaneous fat in female). (Since fat is basically water-free, lean people have a greater proportion of water to total body weight than fat people.) Fluid intake and output Intake : i Preformed Water- water derived from ingested liquids (1600 ml) and foods (700 ml) that has been absorbed from the gastrointestinal tract. C h a p t e r 2 7 4-Primary source of body fluid 2300 ml/day ii Metabolic Water- water produced mainly when electrons are accepted by oxygen during cellular respiration ; and To a smaller extent, water produced during dehydration synthesis reaction. Both sources amount to 200 ml/day . *Total fluid input (preformed and metabolic) averages about 2500 ml/day Output : Avenues of Fluid Output Kidney 1500 ml Evaporation 400 ml Perspiration 100 ml Lungs 300 ml GI tract 200 ml 2500 ml/day *Under normal circumstances, fluid intake equals fluid output, so the body maintains a constant volume. (Fluid Intake = Fluid Output) Regulation of Fluid Gain Fluid gain due to formation of metabolic water is not regulated to maintain homeostasis of body water....
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CHAP27_2402 - C h a p t e r 2 7 1 BIOLOGY 2402 Anatomy and...

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