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Published byNicholas Mathews Modified over 9 years ago
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Acid-Base Balance
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Blood - normal pH of 7.2 – 7.45 7.45 = alkalosis 3 buffer systems to maintain normal blood pH 1. Buffers 2. Removal of CO 2 by lungs 3. Removal of H + ions by kidneys
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The Negative logarithmic relationship between [H + ] and pH
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Acids are H + donors. Bases are H + acceptors, or give up OH - in solution. Acids and bases can be: Strong – dissociate completely in solution HCl, NaOH Weak – dissociate only partially in solution Lactic acid, carbonic acid
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The Body and pH Homeostasis of pH is tightly controlled Extracellular fluid = 7.4 Blood = 7.35 – 7.45 8.0 death occurs Acidosis (acidemia) below 7.35 Alkalosis (alkalemia) above 7.45
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Small changes in pH can produce major disturbances Most enzymes function only with narrow pH ranges Acid-base balance can also affect electrolytes (Na +, K +, Cl - ) Can also affect hormones
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The body produces more acids than bases Acids take in with foods Acids produced by metabolism of lipids and proteins Cellular metabolism produces CO 2. CO 2 + H 2 0 ↔ H 2 CO 3 ↔ H + + HCO 3 -
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Control of Acids 1. Buffer systems Take up H+ or release H+ as conditions change Buffer pairs – weak acid and a base Exchange a strong acid or base for a weak one Results in a much smaller pH change
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Bicarbonate buffer Sodium Bicarbonate (NaHCO 3 ) and carbonic acid (H 2 CO 3 ) Maintain a 20:1 ratio : HCO 3 - : H 2 CO 3 HCl + NaHCO 3 ↔ H 2 CO 3 + NaCl NaOH + H 2 CO 3 ↔ NaHCO 3 + H 2 O
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Phosphate buffer Major intracellular buffer H + + HPO 4 2- ↔ H 2 PO4 - OH - + H 2 PO 4 - ↔ H 2 O + H 2 PO 4 2-
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Protein Buffers Includes hemoglobin, work in blood and ISF Carboxyl group gives up H + Amino Group accepts H + Side chains that can buffer H + are present on 27 amino acids.
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2. Respiratory mechanisms Exhalation of carbon dioxide Powerful, but only works with volatile acids Doesn’t affect fixed acids like lactic acid CO 2 + H 2 0 ↔ H 2 CO 3 ↔ H + + HCO 3 - Body pH can be adjusted by changing rate and depth of breathing
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3. Kidney excretion Can eliminate large amounts of acid Can also excrete base Can conserve and produce bicarb ions Most effective regulator of pH If kidneys fail, pH balance fails
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Hydrogen Ion Excretion in Kidney
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Buffering of hydrogen ions in urine
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Decrease H ion secretion and HCO3 ion reabsorption Increase in H ion secretion and HCO3 ion reabsorption PCO2 H, HCO3 ECF volume Angiotensin II Aldosterone HyperkalemiaHypokalemia Factors that increase or decrease H secretion and HCO3 Reabsorption by renal tubules :
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Rates of correction Buffers function almost instantaneously Respiratory mechanisms take several minutes to hours Renal mechanisms may take several hours to days
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Buffers Protein Buffer Systems Amino Acid buffers Hemoglobin buffers Plasma Protein buffers Phosphate Buffer Systems Carbonic Acid – Bicarbonate Buffer System
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Buffer systems are used to keep the body in pH balance (homeostasis) It consists of a weak acid (H + )and its dissociation products (an anion) 3 major buffer systems in human Protein buffer system (includes hemoglobin buffer system) Regulates ICF & ECF (both plasma & interstitial fluid) Most important in ICF & hemoglobin Hemoglobin buffer system = carbonic anhydrase in RBC * it absorbs CO2 from ECF & get immediate effect Amino acids have carboxyl group (gives up H+) and Amino acids have amino group(can accept H+)
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Carbonic acid-bicarbonate buffer system Important in ECF Lots of carbon dioxide from metabolic acids It mixes with water & get carbonic acid which dissociates into H + & HCO3 - Metabolic acids have H+ ; Our body has “bicarbonate reserve” Bicarbonate reserve = ample supply of bicarb in ECF These combine to form CO 2 + H 2 O CO 2 excreted via lungs Think of CO 2 as an acid since it readily combines with water to become carbonic acid
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Maintenance of Acid-Base Balance Respiratory System: removal of CO 2 by lungs – stabilizes the ECF, has direct effect on Carbonic Acid – Bicarbonate Buffer System Urinary System: removal of H + ions by kidneys
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Regulation of blood pH by the respiratory system
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Kidney excretion of H + Metabolic reactions produce nonvolatile acids One way to eliminate this huge load is to excrete H + in urine In the proximal convoluted tubule, Na + /H + antiporters secrete H + as they reabsorb Na + Intercalated cells of collecting duct include proton pumps that secrete H + into tubule fluid; reabsorb K + and HCO 3 - Urine can be up to 1000 times more acidic than blood 2 other buffers can combine with H + in collecting duct HPO 4 2- and NH 3
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Secretion of H + by intercalated cells in the collecting duct
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