Acid Base Balance

Acid Base Balance

*ACIDSAcids can be defined as a proton (H+) donor Hydrogen containing substances which dissociate in solution to release H+H+H+H+H+

*ACIDSPhysiologically important acids include:Carbonic acid (H2CO3)Phosphoric acid (H3PO4)Pyruvic acid (C3H4O3)Lactic acid (C3H6O3)These acids are dissolved in body fluidsLactic acidPyruvic acidCarbonic acidPhosphoric acid

*BASESBases can be defined as:A proton (H+) acceptorMolecules capable of accepting a hydrogen ion (H+)H+H+H+H+

*BASESPhysiologically important bases include:Bicarbonate (HCO3- )Biphosphate (HPO4-2 )BiphosphateBicarbonate

*pH refers to Potential HydrogenExpresses hydrogen ion concentration in water solutionsWater ionizes to a limited extent to form equal amounts of H+ ions and OH- ions H2O H+ + OH- H+ ion is an acid OH- ion is a basepH SCALE

*H+ ion is an acidOH- ion is a base

pH SCALE

*Pure water is Neutral ( H+ = OH- ) pH = 7Acid ( H+ > OH- ) pH < 7Base ( H+ < OH- ) pH > 7Normal blood pH is 7.35 -7.45pH range compatible with life is 6.8 - 8.0pH SCALEACIDS, BASES OR NEUTRAL???123

*pH SCALEpH equals the logarithm (log) of the reciprocal of the hydrogen ion (H+) concentration H+ concentration in extracellular fluid (ECF)pH = log 1 / H+ concentration4 X 10 -8 (0.00000004)

Maintenance of BalanceBalance maintained by:Buffering systems

Lungs

KidneysH2CO3..HCO3

Buffer SystemsPrevent major changes in pHAct as sponges 3 main systemsBicarbonate-carbonic acid bufferPhosphate bufferProtein bufferH+H+H+

Buffers + H H Buffer

Buffer SystemsBicarbonate buffer - most importantActive in ECF and ICFPhosphate buffer Active in intracelluar (ICF) fluidProtein buffer - Largest buffer storeAlbumins and globulins (ECF)Hemoglobin (ICF)

Bicarbonate-Carbonic AcidBodys major bufferCarbonic acid - H2CO3 (Acid)Bicarbonate - HCO3 (Base)

1 20

pH = 7.4H2CO3 HCO324 mEq/L1.2 mEq/L

RegulationKey conceptCarbonic anhydrase equation

CO2 +H2O H2CO3 H+ + HCO3CarbonCarbonic Bicarbonate Dioxide Acid

(ACID) (BASE)

As CO2 increases, carbonic acid increases, H+ ions increasepH drops.. becomes more acidic

CO2 +H2O H2CO3H+ + HCO3Carbonic Bicarbonate Acid CO2 H2CO3 H+ HCO3(pH Acidic

As HCO3 increases, H+ decreasespH rises, becomes more alkaline

CO2 +H2O H2CO3H+ + HCO3Carbonic Bicarbonate Acid CO2 H2CO3 H+ HCO3 (pH Basic >7.45)

Henderson-Hasselbalch EquationpH= pK+ log HCO3/0.03Pco2pH= 6.1+ 1.3= 7.4pK of Bicarb. buffer system= 6.1pK of Phosphate buffer system= 6.8pK of protein system is very close to 7.4

Phosphate Buffer systemICF,ECF, Interstitial fluidComponents are HPO4 & H2PO4Important IC buffer system quantitatively

*ACID-BASE REGULATION

*ACID-BASE REGULATIONMaintenance of an acceptable pH range in the extracellular fluids is accomplished by three mechanisms:1) Chemical BuffersReact very rapidly (less than a second)2) Respiratory RegulationReacts rapidly (seconds to minutes)3) Renal RegulationReacts slowly (minutes to hours)

*ACID-BASE REGULATIONRespiratory RegulationCarbon dioxide is an important by-product of metabolism and is constantly produced by cellsThe blood carries carbon dioxide to the lungs where it is exhaledCO2CO2CO2CO2CO2CO2Cell Metabolism

*ACID-BASE REGULATIONRespiratory RegulationWhen breathing is increased, the blood carbon dioxide level decreases and the blood becomes more BasicWhen breathing is decreased, the blood carbon dioxide level increases and the blood becomes more AcidicBy adjusting the speed and depth of breathing, the respiratory control centers and lungs are able to regulate the blood pH minute by minute

*ACID-BASE REGULATIONKidney RegulationExcess acid is excreted by the kidneys, largely in the form of ammoniaThe kidneys have some ability to alter the amount of acid or base that is excreted, but this generally takes several days

The renal control of acidbase balanceThe only mechanism to excrete non-volatile acids produced during metabolismSecretion of H+Re-absorption of filtered HCO3-Production of new HCO3- in the renal tubules

Mode of H+ secretion and excretionAll parts of the renal tubule except in the descending and ascending thin parts of the loops of HenleLinked to HCO3- reabsorptionNaHCO3 is freely filteredReabsorbed as CO2 after it combines with one secreted H+?Secretion of every H+ leads to the reabsorption of one HCO3-

Secretion of H+ and re-absorption of HCO3-

HCO3- Reabsorption and H+ Secretion in Intercalated Cells of Late Distal and Collecting TubulesSecretion of hydrogen ions in Intercalated cells of distal tubules

Renal Compensations forAcid-Base DisordersRenal compensatory mechanisms

New HCO3-Figure 30-7; Guyton and Hall

Generation of new HCO3 ions

Ammonia buffer systemNew HCO3-Figure 30-8; Guyton and Hall

New HCO3-Figure 30-9; Guyton and Hall

Quantification of renal acid base excretion:Total H+ secretion = 4380 mmol/day= HCO3- reabsorption (4320 mmol/d)+ titratable acid (NaHPO4-) (30 mmol/d)+ NH4+ excretion (30 mmol/d)

Net H+ excretion = 60 mmol/day= titrable acid (30 mmol/d)+ NH4+ excretion (30 mmol/d)

Acid-Base Imbalances

Acidosis (acidemia)pH falls below 7.35Increase in blood carbonic acid or Decrease in bicarbonate

Acid-Base ImbalancesAlkalosis (alkalemia)pH greater than 7.4Increase in bicarbonate or Decrease in carbonic acid

Acid-Base ImbalancesPrimary cause or origin:MetabolicChanges brought about by systemicalterations (cellular level) RespiratoryChanges brought about by respiratory alterations

Acid-Base ImbalancesCompensationCorrective response of kidneys and/or lungs CompensatedRestoration of pH and 20 : 1 ratioUncompensatedInability to adjust pH and 20 : 1 ratio

*ACIDOSIS / ALKALOSISNormal values pH = 7.4PCO2 = 40 mm HgHCO3- = 24 mEq/LpH 7.35 - 7.45PaCO2 35 - 45 mmHgHCO3 22 - 26 mEq /L

Four Basic Types of ImbalanceRespiratory AcidosisRespiratory AlkalosisMetabolic AcidosisMetabolic Alkalosis

*ACIDOSIS / ALKALOSISAcidosisA condition in which the blood has too much acid (or too little base), frequently resulting in a decrease in blood pHAlkalosisA condition in which the blood has too much base (or too little acid), occasionally resulting in an increase in blood pH

Respiratory AcidosisCarbonic acid excessExhaling of CO2inhibitedCarbonic acid builds uppH falls below 7.35Cause = Hypoventilation (see chart) H2CO3

*HYPOVENTILATIONHypo = UnderElimination of CO2H+pH

*RESPIRATORY ACIDOSISThe speed and depth of breathing controls the amount of CO2 in the bloodNormally when CO2 builds up, the pH of the blood falls and the blood becomes acidicHigh levels of CO2 in the blood stimulate the parts of the brain that regulate breathing, which in turn stimulate faster and deeper breathing

Causes of respiratory acidosisDepressed respiratory centersCOPD e.g. asthma, emphysemaAltered gas exchange across respiratory membrane e.g. dec. SA of resp. membrane

Acid-Base ImbalancesNormal

1 20

7.4H2CO3 HCO324 mEq/L1.2 mEq/L

Respiratory Acidosis

1 13 7.21H2CO3 HCO324 mEq/L1.84 mEq/L

Respiratory AcidosisCompensation: How?Opposite regulating mechanismProblem = depressed breathing, build up of CO2 in bloodResponse - Kidney retains HCO3(Response .. Slow)

*RESPIRATORY ACIDOSISBODYS COMPENSATIONkidneys conserve HCO3- ions to restore the normal 40:2 ratio (20:1)kidneys eliminate H+ ion in acidic urineH2CO3HCO3-230:HCO3-H2CO3HCO3-H++acidic urine

Respiratory AlkalosisCarbonic acid deficitIncreased exhalationof CO2Carbonic acid decreasespH rises above 7.45Cause = hyperventilation (see chart)H2CO3

*HYPERVENTILATIONHyper = OverElimination of CO2H+pH

*RESPIRATORY ALKALOSISCan be the result of:1) Anxiety, emotional disturbances2) Respiratory center lesions3) Fever4) Salicylate poisoning (overdose)5) Assisted respiration6) High altitude (low PO2)

Respiratory Alkalosis

1 40 7.70H2CO3 HCO324 mEq/L0.6 mEq/L

Respiratory AlkalosisCompensation: Problem = excess blowing off of CO2Result = decrease in carbonic acid and increase in HCO3Response: Kidney excretes excess bicarbonate

*RESPIRATORY ALKALOSISrespiratory alkalosispH = 7.7hyperactive breathing blows off CO2H2CO30.520:CO2CO2+ H2O

*RESPIRATORY ALKALOSISBODYS COMPENSATION- kidneys conserve H+ ions and eliminate HCO3- in alkaline urine0.515:HCO3-Alkaline Urine

Metabolic AcidosisBase-bicarbonate deficitLow pH (< 7.35) Low plasma bicarbonate (base)Cause = relative gain in H+ (lactic acidosis, ketoacidosis) or actual loss of HCO3 (renal failure, diarrhea)

*METABOLIC ACIDOSISThe causes of metabolic acidosis can be grouped into five major categories1) Ingesting an acid or a substance that is metabolized to acid e.g. aspirin, methyl alcohol2) Abnormal Metabolism e.g. DM3) Kidney Insufficiencies e.g. CRF4) Strenuous Exercise5) Severe Diarrhea 6) Prolonged deep (from duodenum) vomiting can result in the same situation

Metabolic AcidosisKidney failure (decrease in bicarbonate)

1 10 7.10H2CO3 HCO312 mEq/L1.2 mEq/L

Metabolic AcidosisLactic acidosis, keto acidosis (increase acid no change in bicarbonate)

1 10 7.10H2CO3 HCO324 mEq/L2.4 mEq/L

Metabolic AcidosisCompensation: Problem = low HCO3 (base) or high H+ ion (acid)Response: Lungs hyperventilateGet rid of CO2(decrease PaCO2 and therefore raise level of HCO3)

*METABOLIC ACIDOSISBODYS COMPENSATION- hyperactive breathing to blow off CO2- kidneys conserve HCO3- and eliminate H+ ions in acidic urineH2CO3HCO3-0.7510:CO2CO2+ H2OHCO3- + H+HCO3-+H+Acidic urine

Metabolic AlkalosisBicarbonate excessHigh pH (> 7.45)Loss of H+ ion or gain of HCO3 Most common causes vomiting from stomachOther: Abuse of antacids, K+ wasting diuretics

*METABOLIC ALKALOSISCan be the result of:1) Ingestion of Alkaline Substances2) Vomiting ( loss of HCl )

Metabolic Alkalosis

1 30 7.58H2CO3 HCO336 mEq/L1.2 mEq/L

Metabolic AlkalosisCompensation:Problem = too much baseResponse: Lungs compensate by hypoventilatingRetain CO2, increase PaCO2Increase acid level in blood

*METABOLIC ALKALOSISBODYS COMPENSATION- breathing suppressed to hold CO2- kidneys conserve H+ ions and eliminate HCO3- in alkaline urine1.2530CO2+ H2OHCO3- + H+HCO3-H++Alkaline urine:

*ACIDOSISdeepvomitingfrom GI tractkidneydisease(uremia)increase inplasma H+concentrationdepression ofnervous system

*ALKALOSISoverexcitabilityof nervoussystem

27-*Regulation of Acid-Base Balance

27-*Regulation of Acid-Base Balance