ACID-BASE EQUILIBRIAACID-BASE EQUILIBRIACHEMICAL BUFFERS OF CHEMICAL BUFFERS OF

HUMAN BODYHUMAN BODY

ARRHENIUS ACIDS AND BASESARRHENIUS ACIDS AND BASES

Arrhenius defined Arrhenius defined acidsacids as substances that as substances that dissolve in water to release hydrogen dissolve in water to release hydrogen ionsions (H(H++) into ) into solutionsolution. .

HHCl Cl HH++(aq) + Cl(aq) + Cl- - (aq)(aq)

Arrhenius defined Arrhenius defined basesbases as substances that as substances that dissolve in water to release hydroxide dissolve in water to release hydroxide ionsions

(OH(OH--) into ) into solutionsolution. .

NaOH NaOH Na Na++(aq) + (aq) + OHOH- - (aq)(aq)

BrBrØØnsted-Lowrynsted-Lowry acids and basesacids and basesBrBrØØnsted-Lowrynsted-Lowry acidsacids are are donors of protonsdonors of protons (H (H++) while) whilebasesbases are are acceptors of protons.acceptors of protons.

HClHCl HH33OO++(aq) + Cl(aq) + Cl-- (aq) (aq)+ H2O

++

+-

NH3 + H2O NH4+(aq) +OH-

(aq)

+ -donor-K1 acceptor-B2 acceptor-B1donor-K2

acceptor-B1 donor-K1 acceptor-B2donor-K2

STRONG AND WEAK ACIDSSTRONG AND WEAK ACIDS Strong acids completely (100%) Strong acids completely (100%)

dissociate in ions in water solutiondissociate in ions in water solution

HCl + HHCl + H22O HO H33OO++ (aq) + Cl (aq) + Cl--(aq) (aq) (100 % ions)(100 % ions)

Weak acids don’t dissociate completely and the equilibrium is moved toward undissociated acid. Concentrations of H3O+ and (A-) are low.

Keq = [H3O+][A-] [HA][H2O]

Ka = Keq[H2O] = [H3O+][A-] [HA]

HA + H2O HH33OO++ + A + A--

CH3COOH + H2O CH3COO- + H3O+

HA + H2O HH33OO++ + A + A--

PURE WATER IS NEUTRAL!

+ acid (H+)

+ base (OH-)

Ionization of water gives the same concentrations of H+ and OH- ions.

Acidic solution

Basic solution

H2O + H2O H3O + OH-

[H3O+] = 1,0 x 10-7 M[OH-] = 1,0 x 10-7 M

Kw = [ H3O+][ OH- ] = 1,0 x 10-14

Comparison of [HComparison of [H33OO++] and [OH] and [OH--]]

Acidic Basic0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

pH = - log [H3O+] [H3O+] = 1 x 10-4 pH = 4.0[H3O+] = 1 x 10-11 pH = 11.0

Acidic, basic and neutral solution Acidic, basic and neutral solution in our environmentin our environment

pH values of body fluids and erythrocytes

Body fluidsBody fluids pH pH Body fluids Body fluids pHpH

salivasaliva 5,05,06,86,8 Vaginal Vaginal secretionsecretion 3,23,24,24,2

gastric juicegastric juice 1,01,02,02,0 Amniotic fluidAmniotic fluid 7,17,17,57,5small small

intestine intestine juice juice

7,07,08,08,0 Blood plasmaBlood plasma 7,39 7,39 0,05 0,05

bilebile 5,85,88,58,5 erythrocyteserythrocytes 7,36 7,36 0,05 0,05Pancreatic Pancreatic

juicejuice 8,08,08,38,3arterial bloodarterial blood 7,35 7,35 0,10 0,10

urine urine 4,84,87,87,8

pH of BloodpH of BloodpH of blood is 7,4, [H+] = 4 x 10-8 = 40 nmol H+ / L of bloodAllowed variation of pH of blood is pH ± 0,05 or

concentration of H+ ± 5 nmol / L blood

pH < 7,0ARE INCOMPATIBLE WITH LIFE!

pH > 7,8pH = 7,3 [H+] = 5 x 10-8 = 50 nmol H+ / L of bloodDecreasing of pH for 0,1 unit, the concentration of [H+] increases for 25%.

pH = 7,1 [H+] = 8 x 10-8 = 80 nmol H+ / L of bloodDecreasing of pH for 0,3 unit, the concentration of [H+] increases twice.

CHEMICAL BUFFERSCHEMICAL BUFFERS• Buffers are mixtures of weak acids and their Buffers are mixtures of weak acids and their

conjugated strong bases (salts) or mixtures of weak conjugated strong bases (salts) or mixtures of weak bases and their conjugated strong acids. bases and their conjugated strong acids.

• Chemical buffers confer resistance to a change in the pH of a solution when hydrogen ions (protons) or hydroxide ions are added or removed.

• In comparison to buffers, when the acid or base is In comparison to buffers, when the acid or base is added to the water, the pH value changes rapidly.added to the water, the pH value changes rapidly.

Chemical buffers are important for normal function of bood cells. pH value of blood is 7.4. Change of pH of blood can cause disturbance in binding of oxygen and normal function of cell processes.

CHEMICAL BUFFERSCHEMICAL BUFFERSBUFFER: HA (weak acid)/A- (strong conjugated base)

HA H+ + A- NaA Na+ + A-

[HA]]][A[HKa

][A[HA]K][H a

][A[HA]loglogK]log[H- a

[HA]][AlogpKpH a

Henderson-Hasselbachequilibrium

- If [HA] = [A-], then pH = pKa -pH of buffer does not change with dilution of solutions - Efficiency of buffer:

pH = pKa ± 1

1pK1

10logpKpH aa 1pK101logpKpH aa

MECHANISM OF BUFFERS ACTIONMECHANISM OF BUFFERS ACTIONBuffer: HA/A-

HA H+ + A- NaA Na+ + A-

Function of acidic component of buffer:

HA + OH- H2O + A-

Function of basic component of buffer:

A- + H+ HA

[HA]][AlogpKpH a

HA

Henderson-Hasselbach equilibrium

A-

HAA-

HA

A- HA A-

SUMMARY OF BUFFER ACTIONSUMMARY OF BUFFER ACTION

• Weak acid of buffer (HA) neutralizes added Weak acid of buffer (HA) neutralizes added base.base.

• Conjugated base of buffer (AConjugated base of buffer (A--) neutralizes ) neutralizes added acid.added acid.

• pH value of solution is kept unchangeable.pH value of solution is kept unchangeable. HA

HA HAA-

A-A-

BLOOD BUFFERSBLOOD BUFFERSBlood buffers are:

Bicarbonate buffer, H2CO3 HCO3-,

It is the most important inorganic blood buffer. It represents 5% of buffer systems in blood.

Phosphate buffer, H2PO4- HPO4

2-; It represents 1% of buffer capacity of blood.

Proteins buffer, proteine proteinate, It represents 93% of buffer capacity of blood, 80% of itcorresponds to hemoglobin and 13% corresponds to

therest of proteins of blood serum.

Bicarbonate buffer H2CO3 /HCO3-

CO2(aq) + H2O(l) H2CO3 (aq) HCO3-(aq) +H+

(aq)

CO2(aq) + H2O(l) HCO3-(aq) + H+

(aq)

CO2(g) CO2(aq)

• MECANISM OF ACTION:

HCO3-(aq) + H+

(aq) H2CO3 (aq) CO2(aq) + H2O(l)

H2CO3(aq) + OH-(aq) H2O(l) + HCO3

-(aq)

The carbonic acid-hydrogen carbonate ion buffer works throughout the The carbonic acid-hydrogen carbonate ion buffer works throughout the body to maintain the pH of blood plasma close to 7.40.body to maintain the pH of blood plasma close to 7.40.The body maintains the buffer by eliminating either the The body maintains the buffer by eliminating either the acid (carbonic acid (carbonic acid) or the base (hydrogen carbonate ionsacid) or the base (hydrogen carbonate ions).).

[CO2] = 0,03 x p CO2

• Changes in Changes in carbonic acid concentrationcarbonic acid concentration can be effected can be effected within seconds through increased or decreased respiration. within seconds through increased or decreased respiration.

• Changes in Changes in hydrogen carbonate ionhydrogen carbonate ion concentration, however, concentration, however, require hours through the relatively slow elimination through require hours through the relatively slow elimination through the kidneysthe kidneys

Bicarbonate buffer H2CO3 /HCO3-

ALKALOSIS AND ACIDOSISALKALOSIS AND ACIDOSISBlood pH can be disturbed by a number of Blood pH can be disturbed by a number of respiratory and metabolicrespiratory and metaboliccausescauses..

Respiratory AlkalosisRespiratory Alkalosis • Respiratory alkalosis is a condition in which the pH of the blood is Respiratory alkalosis is a condition in which the pH of the blood is

above normal (above normal (pH > 7.4pH > 7.4). ). • The increase in pH value is often caused by hyperventilation The increase in pH value is often caused by hyperventilation

(excessively deep breathing). (excessively deep breathing). • When a person hyperventilates they exhale more carbon dioxide When a person hyperventilates they exhale more carbon dioxide

than normal. As a result the carbon dioxide concentration in the than normal. As a result the carbon dioxide concentration in the blood is reduced and the bicarbonate/carbonic acid equilibrium blood is reduced and the bicarbonate/carbonic acid equilibrium shifts to the left. shifts to the left.

• The corresponding drop in HThe corresponding drop in H33OO++ concentration causes an increase in concentration causes an increase in pH. pH.

• 2 H2 H22O + O + COCO22 H H22COCO33 + H + H22O HO H33OO++ + HCO + HCO33--

• Respiratory alkalosis is treated by having the hyperventilating Respiratory alkalosis is treated by having the hyperventilating person breathe into a paper bag. In doing so, they rebreathe some person breathe into a paper bag. In doing so, they rebreathe some of expelled carbon dioxide, and blood carbon dioxide levels return of expelled carbon dioxide, and blood carbon dioxide levels return to normal. to normal.

Respiratory AcidosisRespiratory Acidosis

Respiratory acidosis is caused by the reverse process (Respiratory acidosis is caused by the reverse process (pH< 7.4pH< 7.4). A ). A hypo ventilating (excessively shallow breathing) person does not hypo ventilating (excessively shallow breathing) person does not expel enough carbon dioxide and has elevated blood carbon expel enough carbon dioxide and has elevated blood carbon dioxide levels. This causes the equilibrium to shift to the right, the dioxide levels. This causes the equilibrium to shift to the right, the HH33OO++ concentration increases and pH drops. concentration increases and pH drops.

2 H2 H22O + O + COCO22 H H22COCO33 + H + H22O HO H33OO++ + HCO + HCO33--

Metabolic AcidosisMetabolic Acidosis Metabolic acidosis is a condition of low blood pH resulting from Metabolic acidosis is a condition of low blood pH resulting from non-respiratory causes. Those processes that remove bases from non-respiratory causes. Those processes that remove bases from the body or produce acids may cause metabolic acidosis. A the body or produce acids may cause metabolic acidosis. A common example is common example is overexertionoverexertion. When a person overly exerts . When a person overly exerts themselves an insufficient supply of oxygen to the active muscles themselves an insufficient supply of oxygen to the active muscles results in the production of large amounts of lactic acid. If the results in the production of large amounts of lactic acid. If the amount of lactic acid produced exceeds the buffering capacity of amount of lactic acid produced exceeds the buffering capacity of the blood, the blood pH will be lowered. the blood, the blood pH will be lowered.

Metabolic AlkalosisMetabolic Alkalosis

• Any condition in which a high blood pH is present due to non-Any condition in which a high blood pH is present due to non-respiratory causes is called metabolic alkalosis. respiratory causes is called metabolic alkalosis.

• In general, those processes that remove acids from the body or In general, those processes that remove acids from the body or produce bases may cause metabolic alkalosis. produce bases may cause metabolic alkalosis.

• One example is One example is the overuse of diureticsthe overuse of diuretics. Diuretics increase the . Diuretics increase the amount of urine excreted from the body and, if the urine carries with amount of urine excreted from the body and, if the urine carries with it large amounts of acids, the blood pH will be increased.it large amounts of acids, the blood pH will be increased.

Treatments of acidosis and alkalosisTreatments of acidosis and alkalosis

• Mild acidosis or alkalosis can often be treated by eliminating the root Mild acidosis or alkalosis can often be treated by eliminating the root cause. Considering our previous examples, this would simply mean cause. Considering our previous examples, this would simply mean reducing the amount of diuretics taken or forcing the person reducing the amount of diuretics taken or forcing the person to restto rest. .

• In extreme cases, intravenous injections of weak acids or bases may In extreme cases, intravenous injections of weak acids or bases may be performed. Bicarbonate (basic) solutions are used for patients be performed. Bicarbonate (basic) solutions are used for patients experiencing extreme acidosis and ammonium chloride (acidic) experiencing extreme acidosis and ammonium chloride (acidic) solutions are used for those with extreme alkalosis. solutions are used for those with extreme alkalosis.

PHOSPHATE BUFFERPHOSPHATE BUFFER H2PO4-

/HPO42-

(KH2PO4 i K2HPO4 in cells)(NaH2PO4 i Na2HPO4 in intercellular solutions)MECANISM OF ACTION:

HPO42- + H+ H2PO4

-

H2PO4- + OH- H2O + HPO4

2-

Phosphate buffer takes place in homeostasis of Phosphate buffer takes place in homeostasis of HCOHCO33- - in kidneysin kidneys

HH22POPO44- - + HCO+ HCO33

- - HH22COCO33 + HPO+ HPO44

2-2-

HH22O +COO +CO22CO2 (aq) + H2O HCO3

- + H+CA

H2PO4-

PHOSPHATE BUFFER PHOSPHATE BUFFER H2PO4-

/HPO42-

HPO42-

+ H+

+ OH-

Blood circulation

H2PO4- + Na+

HPO42- + 2Na+

urine

kidneyscells

Phosphate buffer takes place in homeostasis of Phosphate buffer takes place in homeostasis of HCOHCO33- - in kidneysin kidneys

HH22POPO44- - + HCO+ HCO33

- - HH22COCO33 + HPO+ HPO44

2-2-

HH22O +COO +CO22

CO2 (aq) + H2O HCO3- + H+

CA

Proteins buffer, proteine proteinate HPrPr-)

Groups of proteins which are donors and Groups of proteins which are donors and acceptors of protons:acceptors of protons:––COOH + OHCOOH + OH-- –COO–COO-- + H + H22OO––COOCOO-- + H + H++ –COOH–COOH––NHNH22 + H + H++ –NH–NH33

++

––NHNH33++ + OH + OH-- –NH–NH22 + H + H22O O

Basic groups confer resistance to change of concentration of H+ ions:Pr – NH2 + H+ Pr – NH3

+ Pr - COO- + H+ Pr – COOH

Acidic groups confer resistance to change of concentration of OH- ions: Pr – COOH + OH- Pr - COO- + H2OPr – NH3

+ + OH- Pr – NH2 + H2O

Pr – COOH Pr – COO- + H+; pH = pK(Pr – COOH) + log [Pr – COO-] / [Pr –

COOH];

Pr – NH3+ Pr – NH2 + H+

pH = pK (Pr – NH3+) + log [Pr –NH2] / [Pr –

NH3+]

-OH+H

-OH+H

NH3+

R

Pr COOH -

R

Pr COONH3+

NH2-

R

Pr COO

Henderson-Hasselbach equilibriaobtained from dissocitation of acidic proteins

BLOOD GASSESBLOOD GASSES1.1. Blood rich in carbon dioxide is pumped from Blood rich in carbon dioxide is pumped from

the heart into the lungs through the the heart into the lungs through the pulmonary arteries. (Arteries are blood pulmonary arteries. (Arteries are blood vessels carrying blood away from the heart; vessels carrying blood away from the heart; veins are blood vessels carrying blood to the veins are blood vessels carrying blood to the heart.) heart.)

2. In the lungs, CO2. In the lungs, CO22 in the blood is exchanged for in the blood is exchanged for OO22. .

3. The oxygen-rich blood is carried back to the 3. The oxygen-rich blood is carried back to the heart through the pulmonary veins. heart through the pulmonary veins.

4. This oxygen-rich blood is then pumped from 4. This oxygen-rich blood is then pumped from the heart to the many tissues and organs of the heart to the many tissues and organs of the body, through the systemic arteries. the body, through the systemic arteries.

5. In the tissues, the arteries narrow to tiny 5. In the tissues, the arteries narrow to tiny capillaries. Here, Ocapillaries. Here, O22 in the blood is exchanged in the blood is exchanged for COfor CO22. .

6. The capillaries widen into the systemic veins, 6. The capillaries widen into the systemic veins, which carry the carbon-dioxide-rich blood which carry the carbon-dioxide-rich blood back to the heart. back to the heart.

OXYGENATION (IN LUNGS)HHb + O2 HbO2

- + H+

in erythrocytes from air goes from erythrocytes in erythrocytes to tissues

H+ + HCO3

- CO2 + H2OJust formed in erythrocytes removes by exhalation arrives from tissues.............................................................................................................................

.HHb + O2 + HCO3

- HbO2- + CO2 + H2O

DEOXIGANATIONIn the presence of COIn the presence of CO22 and H and H++ (e.g. (e.g.,, in the muscles), charged groups in the muscles), charged groups are formed on the amino acid residues lining the subunit interface. are formed on the amino acid residues lining the subunit interface. These charged groups are held together by ionic interactions, These charged groups are held together by ionic interactions, forming "salt bridges" between the two subunits, and stabilizing the forming "salt bridges" between the two subunits, and stabilizing the deoxygenated form of hemoglobin.deoxygenated form of hemoglobin.When blood passes through the alveolar capillaries of the lungs, COWhen blood passes through the alveolar capillaries of the lungs, CO22 and Hand H++ are removed from the hemoglobin, and the oxygenated are removed from the hemoglobin, and the oxygenated configuration is favored (right).configuration is favored (right).

DEOXIGANATION (IN TISSUES POOR IN OXYGEN)

CO2 + H2O HCO3- + H+

from tissues in erythro. from tissues in erythrocytes goes into the lungs

H+ + HbO2- HHb + O2

just formed in erythrocytes in erythrocytes goes to tissuesarrives in tissues comes back to the lungs poor in O2

..............................................................................................................................CO2 + H2O + HbO2

- HHb + HCO3- + O2

CO2(aq) + HHb(aq) Hb-CO2(aq) + H+(aq)

In tissues just released by carbamino-hemoglobin deoxigenation in erythrocytes