1 Acid-Base Balance I. Seminar No. 9 - Chapter 21, I. part -

2 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)

3 Q. Which (general biological) factors influence the volume and distribution of body fluids?

4 A. age newborn baby ~ 78 % TBW, adults ~ 60 % TBW sex males %, females % (more fat in the body)

5 Cations and anions in plasma (average concentrations) Cation Molarity (mmol/l) Anion Molarity (mmol/l) CationPos. charge*AnionNeg. charge* Na + K + Ca 2+ Mg Cl - HCO 3 - Prot - HPO 4 2- SO 4 2- Org. A Total positive charge: 154Total negative charge: 154 * Molarity of charge = miliequivalents per liter (mEq/l)

6 Compare: Isotonic solution of NaCl Physiological sol. 0.9 % = 9 g/l = 154 mmol/l Na + Cl mmol/l

7 Commentary - Cations and anions in plasma every body fluid is electroneutral system in univalent ionic species  molarity of charge = molarity of ion (Na +, K +, Cl -, HCO 3 -, lactate - ) in polyvalent ionic species  molarity of charge = charge × molarity of ion Mg 2+  [pos. charge] = 2 × [Mg 2+ ] = 2 × 1 = 2 SO 4 2-  [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

8 Q. Compare the ion composition of the plasma and ICF.

9 A. FeaturePlasmaICF Main cation Main anion Protein content Main buffer base Na + Cl -  HCO 3 - K + HPO 4 2-    HPO 4 2-

10 Q. What are the main dietary sources of Na +, K +, Ca 2+, Mg 2+, Cl - ?

11 A. IonMain dietary source Na + K + Ca 2+ Mg 2+ Cl - common (table) salt, salty products potatoes, vegetables, dried fruits, soya flour milk products, (cottage) cheese, mineral waters green vegetable (chlorophyll) common (table) salt, salty products

12 Q. Calculate the approximate osmolality of blood plasma if: [Na + ] = 146 mmol/l [urea] = 4 mmol/l [glucose] = 5.6 mmol/l

13 A. approximate osmolality is calculated according to empirical relationship: 2 [Na + ] + [urea] + [glucose] = 2× = mmol/kg H 2 O

14 Data derived (calculated) from ionogram SID, AG

15 SID (strong ion difference) strong ions do not hydrolyze in aqueous solution Na +, K +, Cl - SID = [Na + ] + [K + ] - [Cl - ] = – 103 = 43 mmol/l physiological range of SID = 39 – 45 mmol/l

16 Na + Cl - SID K+K+ SID = HCO HPO Prot - SID = buffer bases of plasma

17 AG (anion gap) the extent of unmeasured or unusual anions AG = [Na + ] + [K + ] - [Cl - ] - [HCO 3 - ] AG = = 18 mmol/l physiological range of AG = 12 – 18 mmol/l

18 AG Na + Cl - HCO 3 - AG K+K+ AG = HPO Prot - + SO OA

19 Elevated AG may be caused by various conditions kidney insufficiency (↑ HPO ↑ SO 4 2- ) diabetes, starvation (↑ acetoacetate + ↑ β-hydroxybutyrate) poisoning by methanol (↑ formate HCOO - ) lactoacidosis (↑ lactate) severe dehydratation (↑ proteinates)

20 Metabolic processes produce or consume various acids

21 Metabolism of nutrients from acid-base point of view Food – hydrolysis of nutrients in GIT metabolic reactions in ICF CO 2 (a potential acid) OH - H+H+ acid base reactions in ECF – buffers systems proton consumption reactions proton productive reactions

22 Proton consumption reactions Gluconeogenesis from lactate: 2 lactate H +  1 glucose anion + proton  neutral molecule protons are consumed in the synthesis of non-electrolyte from anion proton consumption is equivalent to OH - production

23 Proton productive reactions anaerobic glycolysis: glucose  2 lactate H + synthesis of urea: CO 2 + NH CO(NH 2 ) OOC-CH=CH-COO - + H 2 O + 2 H +

24 Q. Which compound is the main acid product of metabolism in human body?

25 A. carbon dioxide CO 2 compare daily production of acid equivalents: CO 2 - up to mmol/day H + as NH 4 + and H 2 PO up to 80 mmol/day

26 Q. What kind of food leads to an increased production of OH - ?

27 A. strictly vegetarian diet contains a lot of potassium citrate/malate potassium salts get into blood plasma organic anions enter cells and are metabolized (CAC) K + cations remain in plasma to keep electroneutrality of plasma  HCO 3 - concentration increases result: mild physiological alkalosis Na + Cl - HCO 3 - other anions K+K+ K + Org.anion -

28 Q. How is CO 2 formed in tissues?

29 Endogenous production of CO 2 CO 2 is produced in decarboxylation reactions oxidative decarboxylation of pyruvate  acetyl-CoA two decarboxylations in CAC (isocitrate, 2-oxoglutarate) decarboxylation of aminoacids  biogenous amines non-enzymatic decarboxylation of acetoacetate  aceton catabolism of pyrimidine bases (cytosine, uracil  CO 2 + NH 3 + β-alanine) catabolism of glycine  CO 2 + NH 3 + methylen-THF main sources of CO 2

30 Acid products of metabolism - Overview aerobic metabolism of nutrients  CO 2 anaerobic glycolysis  lactic acid KB production (starvation)  acetoacetic/β-hydroxybutyric acid catabolism of cystein (-SH)  SO H + catabolism of purine bases  uric acid catabolism of phospholipids  HPO H +

31 Buffer systems in blood Buffer systemRelevanceBuffer baseBuffer acidpKApKA Hydrogencarbonate Proteins a Hydrogenphosphate 50 % 45 % 5 % HCO 3 - Protein-His HPO 4 2- H 2 CO 3, CO 2 Protein-His-H + H 2 PO b 6.8 a In plasma mainly albumin, in erythrocytes hemoglobin b The pK A value depends on the type of protein

32 Buffer bases in (arterial) plasma Buffer basemmol/l HCO 3 - Proteins HPO Total

33 Q. Write a general form of Henderson-Hasselbach equation.

34 A. pH = pK A + log

35 Q. What does the buffering capacity depends on?

36 A. buffering capacity depends on: concentration of both components the ratio of both components the best capacity if: [buffer base] = [buffer acid]

37 Hydrogencarbonate (bicarbonate) buffer

38 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.  therefore CO 2 is included into K A H 2 O + CO 2  H 2 CO 3  HCO H : 1 : 0.03 K A eff = effective/overall dissociation constant

39 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) H 2 O + CO 2  H 2 CO 3  HCO H + 1 : traces : 20

40 Compare: CO 2 in water and blood LiquidpH[CO 2 ] : [HCO 3 - ] Carbonated water a Blood b 3.50 – – : : 20 ! a Closed system (PET bottle), 25 °C, pK A1 = 6.37 pH ~ pCO 2 ~ the pressure of CO 2 applied in saturation process b Open system, 37 °C, pK A1 = 6.10 CO 2 continually eliminated, pCO 2 in lung alveoli ~ 5.3 kPa, acid component of bicarbonate buffer

41 Q. Give the Henderson-Hasselbalch equation for the hydrogencarbonate buffer

42 A. pH = log kPa mmol/l

43 Q. Express the changes in the bicarbonate buffer after adding H +.

44 A. protons are eliminated in the reaction with buffer base HCO H +  H 2 CO 3  H 2 O + CO 2

45 Q. Express the changes in the bicarbonate buffer after adding OH -.

46 A. hydroxide ions are eliminated in the reaction with buffer acid H 2 CO 3 + OH -  H 2 O + HCO 3 -

47 Q. Calculate changes in buffer system after adding 2 mmol H + into one liter Initial statusClosed systemOpen system [HCO 3 - ]24 mmol/l [CO 2 +H 2 CO 3 ]1.2 mmol/l pH7.40

48 Initial statusClosed systemOpen system [HCO 3 - ]24 mmol/l22 [CO 2 +H 2 CO 3 ]1.2 mmol/l3.2 pH H + react with buffer base  24 – 2 = 22 HCO CO 2 newly formed CO 2 remain in the system  = 3.2 CO 2

49 Initial statusClosed systemOpen system [HCO 3 - ]24 mmol/l22 [CO 2 +H 2 CO 3 ]1.2 mmol/l pH H + react with buffer base  = 22 HCO CO 2 newly formed CO 2 is eliminated by lungs  = 1.2 CO 2

50 Q. Calculate the ratio of [HCO 3 - ]/[CO 2 +H 2 CO 3 ] at physiological pH.

51 A = log x log x = 1.3 x = = 20 = 20 : 1 = [HCO 3 - ] : [CO 2 +H 2 CO 3 ]

52 Q. Is the bicarbonate buffer more resistant to acids or bases?

53 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

54 Hydrogenphosphate buffer buffer base: HPO 4 2- buffer acid: H 2 PO 4 - occurs mainly in ICF, bones, urine

55 Q. What is the ratio of plasma phosphates at physiological pH?

56 A = log x log x = 0.6 x = = 4  [HPO 4 2- ] : [H 2 PO 4 - ] = 4 : 1

57 Hemoglobin buffer hemoglobin (Hb) contains a lot of histidine histidine (His) non-basic nitrogen weakly basic nitrogen

58 Buffering function of Hb is performed by side chain of histidine imidazol pK B (His) = 8 imidazolium pK A (His) = = 6 pK A (His in proteins) = 6 - 8

59 The next seminar May 15 - Chapter 21, II. part -