acid-base balance. blood - normal ph of 7.2 – 7.45 7.45 = alkalosis 3 buffer systems to...
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Acid-Base BalanceAcid-Base Balance
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Acid - Base Balance
Blood - normal pH of 7.2 – 7.45 < 7.2 = acidosis > 7.45 =
alkalosis 3 buffer systems to maintain
normal blood pH1. Buffers2. Removal of CO2 by lungs3. 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
solutionLactic 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 < 6.8 or > 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 CO2.
CO2 + H20 ↔ H2CO3 ↔ H+ + HCO3
-
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Control of Acids
1. Buffer systemsTake up H+ or release H+ as
conditions changeBuffer pairs – weak acid and a baseExchange a strong acid or base for
a weak oneResults in a much smaller pH
change
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Bicarbonate buffer
Sodium Bicarbonate (NaHCO3) and carbonic acid (H2CO3)
Maintain a 20:1 ratio : HCO3- : H2CO3
HCl + NaHCO3 ↔ H2CO3 + NaCl
NaOH + H2CO3 ↔ NaHCO3 + H2O
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Phosphate buffer
Major intracellular buffer H+ + HPO4
2- ↔ H2PO4-
OH- + H2PO4- ↔ H2O + H2PO4
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 CO2 + H20 ↔ H2CO3 ↔ H+ + HCO3
-
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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Increase in H ion secretion and HCO3 ion reabsorption
Decrease H ion secretion and HCO3 ion reabsorption
PCO2 PCO2
H , HCO3 H , HCO3
ECF volume ECF volume
Angiotensin II Angiotensin II
Aldosterone Aldosterone
Hypokalemia Hyperkalemia
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 CO2 + H2O CO2 excreted via lungs
Think of CO2 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 CO2 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 HCO3
-
Urine can be up to 1000 times more acidic than blood 2 other buffers can combine with H+ in collecting duct
HPO42- and NH3
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Secretion of H+ by intercalated cells in the collecting duct