Fluid, Electrolyte, and Acid Base Homeostasis 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 Plasma = fluid portion of blood

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

Fluid Compartments, 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

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

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

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

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

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

Distribution of Electrolytes

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

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

Acid-Base Balance Carbonic Acid - Bicarbonate Buffer Phosphate 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)

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