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Chapter 27

Chapter 27. Fluid, Electrolyte, and Acid Base Homeostasis. Fluid Compartments, Fluid Balance. Fluid separated by semi-permeable membranes into compartments Four different compartments Intracellular = inside cells Extracellular = outside cells Interstitial = between cells in the tissues

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Chapter 27

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  1. Chapter 27 Fluid, Electrolyte, and Acid Base Homeostasis

  2. Fluid Compartments, Fluid Balance • Fluid separated by semi-permeable membranes into compartments • Four different compartments • Intracellular = inside cells • Extracellular = outside cells • Interstitial = between cells in the tissues • Plasma = fluid portion of blood

  3. Fluid Compartments, Fluid Balance • Total Body Water (TBW) - 42L, 60% of body weight • Intracellular Fluid (ICF) - 28L, 67% of TBW • Extracellular Fluid (ECF) - 14L, 33% of TBW • Interstitial Fluid - 11L, 80% ECF • Plasma - 3L, 20% of ECF

  4. Fluid Compartments, Fluid Balance • Fluid balance • When in balance, required amount of water present and proportioned among various compartments according to their needs • Many things freely exchanged between fluid compartments, especially water • Fluid movements by: • bulk flow (i.e. blood circulations) • diffusion & osmosis - most I overall

  5. Water • General • Largest single component of body, 45-75% of body • Fat is water free so more\less water in body depending on composition

  6. Water • Water balance • Sources for 2500 ml - average daily intake • Metabolic Water • Preformed Water • Ingested Foods • Ingested Liquids • Balance achieved by output = 2500 ml • GI tract • Lungs • Skin • evaporation • perspiration • Kidneys

  7. Regulating Fluid Intake - Thirst • Wetting mucosa of mouth (temporary) • Stretching of stomach • Decreased osmolarity of blood (most I)

  8. Regulation of Fluid Output • Hormonal control • AntiDiuretic Hormone (ADH) • Aldosterone • Atrial Natriuretic Peptide (ANP) • Physiologic fluid imbalances • Dehydration:  blood pressure,  GFR • Overhydration:  blood pressure,  GFR • Hyperventilation - water loss through lungs • Vomiting & Diarrhea - excess water loss • Fever - heavy perspiration • Burns - initial fluid loss

  9. Concentrations of Solutes • Non-electrolytes • molecules formed by covalent bonds • do not form ions in solution • Electrolytes • Molecules formed by ionic bonds • Disassociate into cations (+) & anions (-) in solutions (acids, bases, salts) • 4 I functions in body • essential minerals • control osmosis of water • maintain acid-base balance • conduct electrical current

  10. Distribution of Electrolytes

  11. Electrolyte Balance • Aldosterone • Atrial Natriuretic Peptide • Female sex hormones (Estrogen, Progesterone) • Antidiuretic Hormone • Calcitonin • Parathyroid Hormone

  12. Acid-Base Balance • Normal metabolism produces H+ (acidity) • Three Homeostatic mechanisms: • Buffer systems - instantaneous; temporary • Exhalation of CO2 - operates within minutes; cannot completely correct • Kidney excretion - can completely correct any imbalance (eventually) • Buffer Systems • Consist of a weak acid and the salt of that acid which function as a weak base • Strong acids dissociate more rapidly and easily than weak acids

  13. Acid-Base Balance • Carbonic Acid - Bicarbonate Buffer • A weak base • H+ + HCO3- ---> H2CO3 ----> H2O + CO2 • Phosphate Buffer • NaOH + NaH2PO4 -----> H2O + Na2HPO4 • HCl + Na2HPO4 -----> NaCl + NaH2PO4 • Protein Buffer • Most abundant buffer in body cells and plasma • Amino acids have amine group (proton acceptor, base) carboxyl group (proton donor, acid)

  14. Acid-Base Imbalances • Acidosis • High blood [H+] • Low blood pH, <7.35 • Alkalosis • Low blood [H+] • High blood pH, >7.45

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