Metabolic processes producing andconsuming H+.Buffer systems in the body.Acid-base balance in the body and itscontrol.2011 (E.T.) 1
The production and regulation of hydrogen ions in the body Acids are continuously produced Liquids, food in the body and threaten the normal pH of the body fluidsICT Metabolic processes CO2 H+ OH-ECT CO2 + H2O ⇔ H2CO3 ⇔ HCO3- + H+ ⇔ bufferY Lung Kidneys CO2 HCO3- NH4+, H2PO4-, SO42- 2 ~ 20 mol /d 1 mmol/d 40-80 mmol/d
Sources of acids in metabolism :1/ volatile carbonic acid: ● the source is CO2 - from decarboxylations ● CO2 with water gives weak volatile carbonic acid ● the exchange of CO2 ( 15 – 25 mol . d-1 ) between the blood and the external environment secure the lungs2/ nonvolatile acids: ● sulfuric acid - from sulfur-containing amino acids (Cys + Met) ● phosphoric acid - from phosphorus-containing compounds ● carboxylic acids (e.g. lactate, acetoacetate, 3-hydroxybutyrate), unless they are completely oxidized to CO2 and water ● nonvolatile acids cannot be removed through the lungs, they are excreted by the kidney into the urine ( 40 – 80 mmol . d-1 ) 3
The limit value of pH (blood)Although there is a largeproduction of acidicmetabolites in the body, pH = 7,40concentrations of H+ions in biological fluids [H+] ≅ 40 nmol . l-1are maintained in the The human body isvery more tolerant ofnarrow range: acidaemia (acidosis) than of alkalaemia (alkalosis). pH = 6,80 pH = 7,70 [H ] ≅ 160 nmol . l + -1 [H+] ≅ 20 nmol . l-1 4 Steep decrease or increase of pH may be life-threatening
Buffer systems in organism IVF ISF ICFBuffering system blood plazma erytrocytesHCO3−/H2CO3 + CO2 50 % 33 % 17 % HCO3− HCO3−Protein−/HProtein 45 % 18 % 27 % – proteinsHPO42−/H2PO4− 1% 3 % (org.) anorg. org. 5% (anorg.) 1 % (anorg.) phosphates phosphatesConcentration of 48 ± 3 42 ± 3buffer systems (mmol/ ~ 56 (BBb) (BBp)l) 5
Buffer systems in bloodHydrogen carbonate buffer - the most important buffer in blood CO2 + H2O H2CO3 H+ + HCO3– − − [HCO3 ] [HCO3 ] pH = pK (H 2CO3 ) + log = 6,1 + log [CO 2 + H 2 CO 3 ] [ H 2CO3 ] efEffective concentration of carbonic acid [CO2 + H2CO3] = 0,23 x pCO2 0,23 is the coefficient of solubility of CO2 for pCO2 in kPa Physiological values: pCO2 5,3 kPa ± 0,5 kPa. HCO3- 24 ± 2 mmol/l In these equations, the concentrations [HCO3-] and [CO2+H2CO3] are expressed in 6 mmol/l, not in the basal SI unit mol/l !
The other buffer systems in organismThe protein buffers – mainly albuminH-proteinn− H+ + protein(n+1)− (based on dissociation of histidineIn blood ∼ 7%, important intracellularyHemoglobin buffer O2 pKA ~ 7,8 O2 HHb Hb− + H+ pKA ~ 6,2 HHbO2 HbO2− + H+ Phosphate buffer pKA2 = 6,8 H2PO4− HPO42− + H+It contributes to intracellular buffering, important for buffering of 9urine. In plasma only ∼5%.
Transport of O2 and CO2 between the tissues and lungs– cooperation of hydrogencarbonate and hemoglobine Blood in lungs Blood in tissues Erc Erc O2 O2 O2 O2 O2 O2 HHb HHb HbO2− HCO3 − HCO3− HbO2− H+ H+ HCO3− HCO3− Cl− Cl- H2CO3 H2CO3 CA CA H2O H2O CO2 CO2 CO2 CO2 CO2 CO2 Chloride shift in venous blood 10
TissuespCO2 in arterial blood ∼5,3 kPaCO2 difunding from cells increases pCO2 up to ∼6,3 kPaThe amount of CO2 dissolved in plasma increases, CO2 difuses into ercsHCO3- is formed in red blood cells by the action of carboanhydrase, it partially binds toHb (carbaminohemoglobin)H+ ions are buffered by Hb in ercsConcentration of HCO3- in ercs is higher than in plasma, HCO3- diffuses out of the redcells, Cl- diffuses into the red cell to maintain electroneutrality. (Hamburgers shift)LungpCO2 in alveols is lower than in venous blood, CO2 diffuses into alveols.HCO3- in red blood cells binds H+, that is released at reoxygenation of Hb and CO2 isformed.Concentration of HCO3- in ercs decreases, exchange of bicarbonate for chloride in redblood cells flushes the bicarbonate from the blood and increases the rate of gas exchange 11
Forms of CO2 transport in blood Form of CO2 Occurence in plasma (%) HCO3− ~ 85 Carbamino proteins ~ 10 Physically dissolved ~5 12
The respiratory system regulates acid basebalance by controlling the rate of CO2 removalPeripheral chemoreceptors in arterial walls and centralchemoreceptors in brainIncrease of [H+] in arterias at metabolic disturbances, or ↑of pCO2in CNS activates medullary respiratory center that stimulatesincreased ventilation promoting elimination of CO2Conversely, the peripheral chemoreceptors reflexely suppresrespiratory activity in response to a fall in arterial H+ concentrationresulting from non-respiratory causes. 13
Kidneys function in maintaning acid-base balance Tubular cell Tubular lumen HCO3− HPO42− Activation at Na+ A− alkalemia H+ H+ HCO3− Gln + acidosis NH4+ NH4 + Glu Na+ H2CO3 + acidosis 2-OG ATP H+ H2O CO2 CO2 H2O A− carboanhydrase H2CO3 Cl- Na+ HPO42− HCO3− H+ H+ Na+ Competition with K+ H2PO4− 14 ~30 mmol/day
Kidneys control the pH of body fluids byadjusting three interrelated factors• H+ excretion• HCO3- excretion• ammonia secretion from tubular cells 15
Tub.cell lumen H secretion in proximal tubulus + ATP H+ H+ H+-ATPase Na+ Antiport with Na+H+ secretion in distal tubulus and collecting duct Type A intercalated cells: Active secretion of H+ into urine – H+ -ATPase, H+-K+ -ATPase HCO3- resorption Type B intercalated cells: HCO3- secretion H+ 16
Kidneys and HCO3- Reabsorption of HCO3- occurs in proximal tubulus and A type Reabsorption of HCO3- intercalated cells HCO3- CO2 Secretion of H+ from three H2O H + sources: OH- • CO2 from plasma H2CO3 ca • CO2 from tubular fluid HCO 3 - CO2 CO2 ca •CO2 produced within theCO2 H2O tubular cell OH - H2O H+ ca – carboanhydrase 17
Kidney and NH3 Production of NH3 from glutamate and glutamin in tubular cells is increased at acidosis. NH3 difuses into the tubular gln ATP H + fluid and buffers H+ ions NH4 that are secreted fromglu NH3 tubular cells NH32-oxoglu NH4 H+ Na+ 18
Urinary buffersH+ transporters in tubular cells and collecting duct can secrete H+against the concentration gradient until the tubular fluid becomes 800times more acidic than plasma. At this point, further secretion stops,because the gradient becomes too great for the secretory process tocontinue. The corresponding pH value is 4,5. Tub.cell lumenH+ ions are buffered by: HPO4- ATP HPO4 (filtered from blood) - H+ H2PO4- NH3 secreted from tubular cells H+ Na+ NH3 NH4If more buffer base is available in the urine, more H+ can be secreted 19
Summary of renal responses to acidosis and alkalosisabnormality H+ H+ HCO3- HCO3- pH of Change of pH secretion excretion resorption excretion urine in plasmaAcidosis ↑ ↑ ↑ - acidic Alkalinization to normalAlkalosis ↓ ↓ ↓ ↑ alkaline Acidification to normalKidneys requires hours to days to compensate for changes in body fluid pH(compared to the immediate responses of the body buffers and the few minutedelay before the respiratory systém responds)However, kidneys are the most potent acid-base regulatory system 20
Contribution of liver to maintenance of acid base balance 2-OG Kidneys URINE Liver acidemia + Gln Gln NH4+ NH4+ + NH3 2NH4+ H+ acidemie AK urea CO2 + H2O H2CO3 H+ + HCO3− urea Two ways of NH3 elimination in the liver urea synthesis (connected with release of 2H+ - acidifying process) glutamin synthesis (without release of H+)Higher synthesis of glutamin is stimulated at acidosis, synthesis of urea is 21potentiated at alkalosis.
Main indicators of acid-base stateMeasured parameters pH 7,40 ± 0,04 pCO2 5,3 ± 0,5 kPa (pO2, Hb, HbO2, COHb, MetHb) Measuring by means of acid-base analyzers 22
Derived (calculated) parametersActual HCO3− concentration 24 ± 3 mmol/lis the concentration of bicarbonate (hydrogen carbonate) in the plasma ofthe sample. It is calculated using the measured pH and pCO2 values.Base excess (BE, base excess) 0 ± 3 mmol/lis the concentration of titratable base when the blood is titrated with astrong base or acid to a plasma pH of 7.40 at a pCO2 of 5.3 kPa and 37°C at the actual oxygen saturation.It is calculated for plasma, blood or extracelular fluid.Arterial oxygen saturation (sO2) 0,94–0,99is defined as the ratio between the concentrations of O2Hb and HHb +O2HbInformation about contration of the main electrolytes (Na+, K+, Cl−, Pi) and 23albumin are also important
Dependent and independent variables of acid basebalance • Dependent variables: pH, BE a HCO3- These variable are not subject to independent alteration. Their concentrations are governed by concentrations of other ions and molecules. • Independent variables: pCO2, SID, weak nonvolatile acids Atot the concentration of each of the dependent variables is uniquely and independently determined by these three independent variables (primary changes in concentrations of some cations (mainly Na+) and anions (Cl−, albumin, phosfphate and unmeasured ions) triggers consequently the changes of acid-base 24 parameters).
The complementary calculations are derived from principle of plasma electroneutrality[Na+] + [K+] + [Ca2+] + [Mg2+] = ([Cl-] + [HCO3-] + [albx-] + [Piy-] + [UA-]) UA- - unmeasured anions (see later) 25
Some complementary calculations Anion gap 150 AG = [Na+] + [K+] − ([Cl−] + [HCO3−]) Na+ Cl- Cl- 16 ± 2 mmol/l 100 HCO3- Higher value of AG indicates the presence of extra K+ unmeasured anions e.g. lactate, acetoacetate, 3- 50 Albx- hydroxybutyrate. Ca2+ AG Piy- The value is often corrected on serum albumin Mg2+ UA- concentration: *AGkorig=AG + 0.25 x ([Alb]norm- [Alb]zjišt* Information about empirical formulas are given only for ilustration, students neednot to know them 26
Some complementary calculationsAlbumin charge Albx-It is calcultaed from albumin concentration (g/l) and pH 11,2 mmol/l at pH =7,4 a [alb]= 40 g/lPhosphate charge Piy-It is calculated from pH and concentration of phosphates 1,8 mmol/l at pH =7,4 a [Pi]=1 mmol/lCorrected chloride ion concentrationcorrecting the chloride concentration for changes in Na+[Cl]kor = [Cl]zjišt.x [Nanorm.] / [Nazjišt] 27
Some complementary calculationsUnmeasured anions[UA] = ([Na+] + [K+] + [Ca2+] + [Mg2+]) – ([Cl−] + [HCO3−] +[Albx-] +[Piy-] ) 6-10 mmol/lUA expresses the concentration of other 150anions that are not included in theequation of electroneutrality (e.g.lactate, Na+ Cl- Cl-keton bodie, glycolate at poisonning withethylene glycol, formiate at poisonning 100with methanol, salicylates etc.)Increased value of UA is compensated by HCO3- K +decrease of concetration of other anionsor mainly HCO3- 50 Albx- Ca2+ Piy- Mg2+ 28 UA-
Some complementary calculationsSID (strong ion difference)SIDeff = [Na+] + [K+] + [Ca2+] + [Mg2+] – ([Cl-] + [UA-])38–40 mmol/l 150Accurate measurement of SID iscomplicated by difficulties with Cl- Cl- Na +determination of UA (unmeasured 100anions), empirical relation is thereforeused HCO3-SIDeff = [HCO3−] + 0,28∙[albumin] + 1,8∙[Pi] K+[Pi] and [HCO3-] are in mmol/l and albumin in SID 50g/l Albx- Ca2+ Piy- Mg2+ UA- 29
Classification of acid-base disorders„acidosis“ (pH < 7,36) metabolic disorder [HCO3-] pH = pK H CO + log 2 3 [CO2 + H2CO3 ]„alkalosis“ (pH > 7,44) respiratory disorder 30 Disturbances are often combined.
Classification of acid-base disorders according to the primary cause Respiratory disorder the primary change in pCO2 due to low pulmonary ventilation or a disproportion between ventilation and perfusion of the lung. Metabolic disorder the primary change in buffer base concentration (not only HCO3–, but also due to changes in protein, phosphate, and strong ions concentrations).Quite pure (isolated) forms of respiratory or metabolic disorders dont exist infact, because of rapid initiation of compensatory mechanisms; however, fullstabilization of the disorder may settle in the course of hours or days. 31
− HCO3 20 pH = 6,1 + log = 6,1 + log = 7,4 pCO2 .0,22 1 Change of Change of the ratio Change of Typ acute parameter HCO3-/pCO2 pH disturbancepCO2 ↑ Resp.acidosis ↓ ↓HCO3 - -concentrationpCO2 ↓ Resp. ↑ ↑ alkalosisChange of HCO3 - -concentrationpCO2 - Metab. ↓ ↓ acidosisHCO3- ↓concentrationpCO2 - Metab. ↑ ↑ alkalosisHCO3- ↑concentration 32
The classification of A-B disorders accordingto time manifestation acute (uncompensated) stabilized (compensated) - simple metabolic disorders or simple respiratory disorders practically do not exist, because the compensation processes begin nearly immediately, however the stabilization can also take some days (in dependence on the type of disorder) 33
Compensatory processesCompensationThe secondary, physiological process occurring in response toa primary disturbance in one component of acid/baseequilibrium wherebythe component not primarily affected changes in such adirection as to restore blood pH towards normal.Metabolic disorders of acid-base balance are modified byrespiratory compensation and oppositelyCorrectionThe secondary, physiological process occurring in response toa primary disturbance whereby the component that isprimarily affected is restored to normal. 34.
Time course of regulatory responsesBuffer systems Organ ECT ICT bone lung liver kidneyFull immed min/hours h/days Development of hours/days daysefectivity iately compenzation The primary respiratory disorder leads to a compensatory change in HCO3– reabsorption by the kidney, which reaches its maximal effectivity in 5 – 7 days. In the primary metabolic disorder, a change in blood pH evokes a rapid change in the pulmonary ventilation rate (during 2 – 12 hours). 35
Acid-base balance graph → overall evaluation (pH, pCO2 a BE) of acid base balance 7,1 7,2 7,3 7,37 7,43 pH 12,0 7,5 10,6 uRAc 9,8 aRAc 7,6 8,0 uMAlk 6,7pCO2 normal 5,3 aMAlk(kPa) aMAc values 4,0 uMAc 2,7 1,3 uRAlk aRAlk -20 -10 0 10 20 30 BE (mmol/l) 36 Ac acidosis, Alk alkalosis; M metabolic, R respiratory; a accute, u stabilized
Example of acid-base balance disturbanceMetabolic acidosis (MAc)Causes of MAc• Increased production of H+ - lactacidosis - ketoacidosis (starvation, non-compensated DM) - acidosis from retention of non volatile acids in renal failure2. Exogenous gain of H+ - metabolites at intoxication with methanol, ethylen glycol, - overdosing with acetylsalicylic acid - NH4Cl infusion at the treatment of MAlk3. Loss of HCO3- - diarhea, burns, renal disturbances4. Relative dilution of plasma – excessive infusion of isotonic solutions 37
Correction and compensation of MAc↑H+ 1. Effect of buffers : H+ + HCO3- → H2CO3 → H2O + CO2 − HCO3- ↓ HCO3 20 < pH <7.4 pCO2 .0,22 1 2. respiratory compensation – increase of pulmonary ventilation − HCO3 20 pCO2 ↓ ≈ pCO2 .0,22 1 pH approches to 7,4, but concentrations of HCO3- and pCO2 are non physiological 3. Renal correction (development during 2–3 days) - acidic urine is excreted. Excretion of H+ is accompanied by excretion of the given anion (A−) (lactate, acetacetate, 3-hydroxybutyrate). HCO3− consumed during buffering reaction is 38 regenerated in renal tubuli.
Grafical description of changes during compensation and correction of MAc 7,1 7,2 7,3 7,37 7,43 pH 12,0 7,5 10,6 uRAc 9,8 aRAc 7,6 8,0 uMAlk 6,7pCO2 normal(kPa) 5,3 aMAc 1 aMAlk 3 values 4,0 uMAc 2 2,7 1,3 uRAlk aRAlk -20 -10 0 10 20 30 BE (mmol/l) 39
Changes of electrolyte parameters during acid-base disturbances (example)AcidosisThe cause: loss of HCO3-(e.g.diarrhea) Na + Cl Cl- - Loss of HCO3- is replaced by Cl- → hyperchloremic acidosis HCO3- K+ SID ↓ 50 Albx- Ca2+ Piy- Mg2+ UA- 40 UA not changed AG not changed
Acidosiscause – production of lactate, keton bodies, formiate,salicylate etc. Due to buffering reaction 150 concentration of [HCO3-], event. Albx- a Piy- is decreased Na + Cl Cl- - Concentration of unmeasured anions (UA) increases HCO3- Concentration of chlorides K+ SID ↓ 50 is not changed – Albx- normochloremic acidosis Ca2+ Piy- Mg2+ UA- UA ↑ AG ↑ 41
Dilution acidosis – consequence of plasma dilution By the dilution the 150 concentration of buffer bases falls Cl Cl- - Na + HCO3- K+ SID ↓ 50 Albx- Ca2+ Piy- Mg2+ UA- AG ↓ 42 UA ↓
Evaluation of acid –base parameters (1)1/ pH, pCO2, BE – type of disturbance, measure of compensation pH= 7,367, pCO2 = 5,25 kPa, BE = - 2,5 mmol.l-1 45
Evaluation of acid –base parameters (2)2/ recalculation of laboratory results• calculation of [Albx-] and [Piy-]• calculation of unmeasured anions [UA-]• correction of Cl- to actual content of water 46
Evaluation of acid –base parameters (2) the deviations of patient values from the reference values are filed to the columns „acidosis“ / „alkalosis“ (according to their signs: „+“ for increase, „−“ for decrease) mmol . l-1 patient acidosis alkalosis[Na+] 140 − +[Cl-]correc 100 + −[UA-]correc 8 + −[Pi-] 2 + −[Alb-] 12 + − 47