Acid-Base Balance I. Seminar No. 9 - Chapter 21, I. part - Homeostasis = maintenance of constant parameters of internal environment (= ECF) * volumes of all body fluids (isovolemia) * concentrations of cations/anions in body fluids (isoionia) * osmolality of body fluids (isotonia) * body temperature (isothermia) * pH of body fluids (isohydria) Q. Which (general biological) factors influence the volume and distribution of body fluids? A. age * newborn baby ~ 78 % TBW, adults ~ 60 % TBW sex * males 55-70 %, females 45-60 % (more fat in the body) Cations and anions in plasma (average concentrations) Compare: Isotonic solution of NaCl Physiological sol. 0.9 % = 9 g/l = 154 mmol/l Commentary - Cations and anions in plasma * every body fluid is electroneutral system * in univalent ionic species TH molarity of charge = molarity of ion (Na^+, K^+, Cl^-, HCO[3]^-, lactate^-) * in polyvalent ionic species TH molarity of charge = charge × molarity of ion Mg^2+ TH [pos. charge] = 2 × [Mg^2+] = 2 × 1 = 2 SO[4]^2- TH [neg. charge] = 2 × [SO[4]^2-] = 2 × 0.5 = 1 * proteins (mainly albumin) are at pH 7.40 polyanions * org. acid anions (OA) -- mainly lactate (AA, oxalate, citrate, ascorbate ...) * charge molarity of proteins + OA is estimated by empirical formulas Q. Compare the ion composition of the plasma and ICF. A. Q. What are the main dietary sources of Na^+, K^+, Ca^2+, Mg^2+, Cl^- ? A. Q. Calculate the approximate osmolality of blood plasma if: [Na^+] = 146 mmol/l [urea] = 4 mmol/l [glucose] = 5.6 mmol/l A. approximate osmolality is calculated according to empirical relationship: 2 [Na^+] + [urea] + [glucose] = 2×146 + 4 + 5.6 = 301.6 mmol/kg H[2]O Data derived (calculated) from ionogram SID, AG SID (strong ion difference) * strong ions do not hydrolyze in aqueous solution * Na^+, K^+, Cl^- * SID = [Na^+] + [K^+] - [Cl^-] = 142 + 4 -- 103 = 43 mmol/l * physiological range of SID = 39 -- 45 mmol/l SID = buffer bases of plasma AG (anion gap) * the extent of unmeasured or unusual anions * AG = [Na^+] + [K^+] - [Cl^-] - [HCO[3]^-] * AG = 142 + 4 - 103 - 25 = 18 mmol/l * physiological range of AG = 12 -- 18 mmol/l AG Elevated AG may be caused by various conditions * kidney insufficiency (-^ HPO[4]^2- + -^ SO[4]^2-) * diabetes, starvation (-^ acetoacetate + -^ b-hydroxybutyrate) * poisoning by methanol (-^ formate HCOO^-) * lactoacidosis (-^ lactate) * severe dehydratation (-^ proteinates) Metabolic processes produce or consume various acids Metabolism of nutrients from acid-base point of view Proton consumption reactions Gluconeogenesis from lactate: 2 lactate^- + 2 H^+ (r) 1 glucose anion + proton (r) neutral molecule Proton productive reactions ^* anaerobic glycolysis: glucose (r) 2 lactate^- + 2 H^+ * synthesis of urea: Q. Which compound is the main acid product of metabolism in human body? A. carbon dioxide CO[2 ]compare daily production of acid equivalents: CO[2] - up to 25 000 mmol/day H^+ as NH[4]^+ and H[2]PO[4]^- - up to 80 mmol/day Q. What kind of food leads to an increased production of OH^-? A. Q. How is CO[2] formed in tissues? Endogenous production of CO[2 ]* CO[2] is produced in decarboxylation reactions * oxidative decarboxylation of pyruvate (r) acetyl-CoA * two decarboxylations in CAC (isocitrate, 2-oxoglutarate) * decarboxylation of aminoacids (r) biogenous amines * non-enzymatic decarboxylation of acetoacetate (r) aceton * catabolism of pyrimidine bases (cytosine, uracil (r) CO[2] + NH[3] + b-alanine) * catabolism of glycine (r) CO[2] + NH[3] + methylen-THF Acid products of metabolism - Overview [* ] aerobic metabolism of nutrients (r) CO[2 ]* anaerobic glycolysis (r) lactic acid * KB production (starvation) (r) acetoacetic/b-hydroxybutyric acid ^* catabolism of cystein (-SH) (r) SO[4]^2- + 2 H^+ * catabolism of purine bases (r) uric acid * catabolism of phospholipids (r) HPO[4]^2- + H^+ Buffer systems in blood Buffer bases in (arterial) plasma Q. Write a general form of Henderson-Hasselbach equation. A. Q. What does the buffering capacity depends on? A. * buffering capacity depends on: * concentration of both components * the ratio of both components * the best capacity if: [buffer base] = [buffer acid] Hydrogencarbonate (bicarbonate) buffer Carbonic acid in vitro * weak diprotic acid (pK[A1] = 6.37; pK[A2] = 10.33) * does exist only in aq. solution, easily decomposes to CO[2] and water [* ] CO[2] predominates 800 ´ in sol. TH therefore CO[2] is included into K[A ] Carbonic acid in vivo * formation catalyzed by carbonic anhydrase * under physiological conditions: pK[A1] = 6.10 * CO[2] is continually eliminated from body by lungs * the overall concentration of carbonic acid: [CO[2] + H[2]CO[3]] = pCO[2] × s = 0.23 pCO[2] (kPa) Compare: CO[2] in water and blood Q. Give the Henderson-Hasselbalch equation for the hydrogencarbonate buffer A. Q. Express the changes in the bicarbonate buffer after adding H^+. A. protons are eliminated in the reaction with buffer base HCO[3]^- + H^+ (r) H[2]CO[3] (r) H[2]O + CO[2 ]Q. Express the changes in the bicarbonate buffer after adding OH^-. A. hydroxide ions are eliminated in the reaction with buffer acid H[2]CO[3] + OH^- (r) H[2]O + HCO[3]^- ^ Q. Calculate changes in buffer system after adding 2 mmol H^+ into one liter Q. Calculate the ratio of [HCO[3]^-]/[CO[2]+H[2]CO[3]] at physiological pH. A. 7.40 = 6.1 + log x log x = 1.3 x = 10^1.3 = 20 = 20 : 1 = [HCO[3]^-] : [CO[2]+H[2]CO[3]] Q. Is the bicarbonate buffer more resistant to acids or bases? A. * see previous problem * [HCO[3]^-] : [CO[2]+H[2]CO[3]] = 20 : 1 * the concentration of buffer base is 20 × higher than the concentration of buffer acid * conclusion: bicarbonate buffer is 20 × more resistant to acids Hydrogenphosphate buffer ^* buffer base: HPO[4]^2- * buffer acid: H[2]PO[4]^- * occurs mainly in ICF, bones, urine Q. What is the ratio of plasma phosphates at physiological pH? A. 7.40 = 6.80 + log x log x = 0.6 x = 10^0.6 = 4 TH [HPO[4]^2-] : [H[2]PO[4]^-] = 4 : 1 ^ Hemoglobin buffer * hemoglobin (Hb) contains a lot of histidine Buffering function of Hb is performed by side chain of histidine The next seminar May 15 - Chapter 21, II. part -