Biochemical mechanismsof acid base balance and acid base disorders

Biochemical Mechanisms of Acid-Base Balance and

Acid Base disorders Dr. Rohini C Sane

Acid-base balance

Site pH maintained under physiological conditions

Arterial blood 7.4

Venous blood 7.43

Intestinal fluid Between plasma & cells

Osteoblast 8.0

Prostrate 5.0

Mitochondria 6.6

Acids & Bases

Acid : yields H⁺ ions ( HCl H⁺ + Cl⁻ )

Base :combines with H⁺ ions ( Na⁺ + HCO₃⁻ ) combines with H⁺

HCl ( strong acid ) H⁺ + Cl⁻ ( weak base )

Conjugate acid base pair

H₂CO₃( weak acid ) H⁺ + HCO₃⁻ ( strong base )

Buffers & their types involved in Acid-base balance

Buffers : solutions resists the change in p H on addition of acid or base

Acidic buffer : weak acid + its salt with strong base

eg H₂CO₃( weak acid ) + NaHCO₃⁻ ( strong base )

Basic /Alkaline buffer : weak base + its salt with strong acid

eg NH₄OH + NH ₄Cl

Mechanism of action of Buffer system for acid base balance

HA weak acid

BA salt of weak acid

A- largely salt component of buffer

Added strong base HA ACID

(OH⁻) H⁺

A- HA (weak acid )

H⁺ OH⁻ (H⁺)Added strong acid

(H₂O)

BA B⁺ + A ⁻

Acids produced in a human body during metabolisms

• Carbonic acid - oxidation of carbon compounds ---CO₂—H ₂ CO₃

• Sulphuric acid - oxidation of sulphur containing amino acids (Cysteine ,Cystine, Methionine)

• Phosphoric acid –metabolism of Phospho proteins ,nucleoproteins, phosphatides

• Organic acids –metabolism of fat ,protein, carbohydrates (Pyruvic acid ,Lactic acid, Acetic acid)

• Latrogenic –Medicines like NH₄Cl , Mandelic acid

Regulation of pH in body *( acid base balance )

FRONT LINE DEFENSE :

Buffer systems

Respiratory mechanism –increased or decreased excretion of CO₂ depending upon need therefore concentration ofH2CO3 (Carbonic acid ) or base in extracellular fluid maintained.

SECOND LINE DEFENSE (KIDNEY ):

Renal mechanisms – excretion of acids or base (concentration of hydrogen (H⁺ ),bicarbonate ( HCO⁻³) controlled.

DILUTION FACTOR :

Acids are diluted in extra cellular fluid (adverse effects in dehydration )

BLOOD BUFFERS INVOLVED IN ACID BASE BALANCE site of acids /alkali production in tissue site of their excretion at( Lung, kidney)

PLASMA BUFFERS

a) Na HCO₃ /H₂CO ₃

b) Na ₂ HPO₄/NaH ₂PO ₄

c) Na –Protein /H-Protein

d) Na organic acids /H –organic acids

BUFFERS OF RED BLOOD CELLS

a) K HCO ₃ /H ₂ CO ₃

b) KHPO₄ / KH₂PO ₄

c) K Hb /HHb

d) KHbO ₂ /HHbO ₂

Bicarbonate Buffer System in acid base balance• Ratio -NaHCO3 :H2CO3= 20: 1 (plasma under physiological conditions )

Advantagesa) High concentration

b) produces volatile & weak acid H₂CO₃

c) physiological buffer front line defenseDisadvantages

• PKA≠ Physiological pH

Neutralization of acids by Bicarbonate Buffer salt component of buffer strong acid (non volatile) added

NaHCO ₃ H+L

_

Na+

H CO3 _

↘ ↙ H+

L_

H₂CO₃

H₂CO₃ ( Carbonic acid ) weak & volatile CO ₂(eliminated by lungs ) + H ₂ OBicarbonate buffer system linked up with respiration.

Bicarbonate Buffer System in acid base balance

strong base added

NaOH H₂CO₃

Na +

OH ⁻ H+

HCO₃_

↘ H₂O ↙

NaHCO ₃ weak base

Bicarbonate Buffer System in acid base balance

Phosphate buffer system in acid base balance

Ratio in plasma : Na₂HPO₄ : NaH₂PO ₄ = 4 : 1 maintained constant by kidney

• Ratio in urine: Na ₂ HPO ₄ :NaH ₂PO₄ = 1 :9

↙Na₂HPO₄↘ HCl (Strong acids added )

Na +

NaHPO4-

H +

Cl-

↘ ↙

NaCl + NaH₂PO₄(excreted in urine)urinary pH decreases

↙ NaH₂PO₄↘ NaOH (strong base added )

NaHPO4-

H +

OH-

Na+

Na₂HPO₄ + H ₂O excreted in urine –pH of urine increases

Phosphate buffer system works in conjugation with kidney.

Advantage : PKa = Physiological p H

Disadvantage: low concentration (2) Physiologically less effective

Protein buffer system in acid base balance

Na + Pr⁻ /H + Pr⁻ ← Plasma

K Hb / HHb ← Erythrocytes

I

1 gm. Hemoglobin= 0.183 mequ H+

1 gm. protein = 0.110 mequ H+

II

Hb / 1000 ml of blood = 27.5 mequ H+

Protein / 1000 ml of blood = 4.24 mequ H+

Hb has more buffering action than plasma proteins

Protein buffer system in acid base balance

• (1 )Buffering action of proteins

(2 ) Na proteinate ( salt component )

Na⁺Pr ⁻ + HL Na L + H ⁺Pr ⁻ (weak acid )

(3 ) formation of carbamino compounds

PrNH₂ + CO ₂ PrNH COOH

p H of medium Protein acts as Charge on protein

Acidic Base Positive ( NH₂ NH₃ ⁺ )

alkaline Acidic Negative ( COOH C00⁻ + H ⁺)

Hemoglobin buffer system in acid base balance

1. COOH

2. NH₂

3. Gaunido group differential ionization of groups based upon pH of ompartment

4. Imidazole group

38 Imidazole groups (from 38 Histidine present in Hb )

(a ) Fe ²⁺ containing group which concerned with O₂ carrier.

TYPE OF GLOBIN CHAIN Histidine linked with Fe ²⁺

Alpha 87 th

Beta 92 th

Alkalinity favors oxygenation


In alkaline medium –imidazole N₂ donates H⁺ (behaves as a acid )

In acidity medium - imidazole N₂ accepts H⁺ (behaves as a base )

TISSUE P CO ₂ Condition Reaction of Hb

Lung LOW Alkaline OxygenationRelease of H⁺Release of CO₂

Tissue HIGH Acidic De oxygenationHb accepts H⁺ to form reduced hemoglobin (HHb) CO₂(Carbamino compounds )CO₂ -Formation of H₂CO₃


Hemoglobin buffer system *( Imidazole group ) for acid base balance

Conditions -Alkaline ( H⁺ low ), PO₂ High , PCO ₂ LOW

Changes in Hb- oxygenation ,release of CO ₂,Release of H⁺

Conditions –Acidic ( High H⁺ ), PO₂ low , PCO ₂ high

Changes in Hb- de oxygenation ,binding of CO ₂,binding of H⁺

Acts as a acid gives proton ↓ Acts as a base & takes up proton

↓

Hemoglobin buffer system *( Imidazole group ) for acid base balance


Hemoglobin buffer systemin acid base balance(in tissue )

Hemoglobin buffer systemin acid base balance(in lungs )

Role of respiratory system in acid base balance :Mechanism

• Sensitivity of respiratory Centre ( RC ) to changes in p H & CO ₂

• Diffusibility of CO ₂ from Blood to alveolar air

• Hyperventilation- high speed /deep

• Hypoventilation- slow (kasumal ) / shallow

• NaHCO₃ : H₂CO₃ = 20: 1 ( maintained constant by respiratory system under physiological conditions )

PCO ₂ H⁺ RESPIRATORY CENTRE VENTILATION STATUS OF CO₂

HIGH HIGH STIMULATED HYPERVENTILATION EXCESS OF CO₂ REMOVED

LOW LOW REPRESSED HYPOVENTILATION CO₂ RETENTION

Role of respiratory system in acid base balance :Mechanismduring acidosis

Role of respiratory system in acid base balance :Mechanism during acidosis

Role of respiratory system in acid base balance :Mechanism during alkalosis

Renal Mechanism for Acid –Base balance1. Elimination of non volatile acids ,Lactic acids, H₂SO₄ buffered with cations (Na⁺ ) are removed by glomerular filtration

2. (Na⁺ ) ↔ H⁺ across tubular membrane to prevent loss of Na⁺

• H⁺ secretion ,NaHCO₃ recovery

• Loss of Na ⁺ is prevented by :

a) Bicarbonate mechanism

b) Phosphate mechanism

c) Ammonia mechanism

3. HCO³⁻ reabsorption

4. NH ₃ production

Bicarbonate mechanism of proximal renal tubular cells for acid base balance

BLOOD Proximal tubular cells Tubular filtrate

CO2 CO2↘

Carbonic unhydrase * H₂ CO₃

H₂O H₂O↗ ↙ * ↘

↙HCO₃⁻ HCO₃⁻ H⁺ H⁺ H₂ CO₃

NaHCO₃⁻

↖Na ⁺ Na ⁺ Na ⁺+ HCO₃⁻

NaHCO₃⁻



The exchange of H⁺ ions proceed first against Sodium Bicarbonate

1. Complete reabsorption of NaHCO₃

2. Reduction of H⁺ ions load of plasma with little change in pH of urine



Factors affecting bicarbonate reabsorption in proximal renal tubular cells

1. pCO₂

2. Concentration of K⁺ in ICF ( intracellular fluid )

3. Plasma Concentration of Cl⁻

4. Concentration of adreno-corticoids Hormones


Factors affecting bicarbonate reabsorption

1. pCO₂

pCO₂ ↑ H₂CO₃↑ H⁺ secretion↑ HCO₃⁻reabsorption ↑ HCO₃⁻ excretion in urine ↓

pCO₂↓ H₂CO₃↓ H⁺ secretion ↓ HCO₃⁻reabsorption↓ HCO₃⁻ excretion in urine ↓

Urine alkaline

urine acidic



2a. Concentration of K⁺ in ICF ( intracellular fluid )

K⁺( ICF )concentration ↑

HCO₃⁻ excretion ↑, HCO₃⁻ absorption↓

HCO₃⁻ secretion↓

Urine alkaline



2 b. Concentration of K⁺ in ICF ( intracellular fluid )

K⁺( ICF )concentration ↓

HCO₃⁻ excretion ↓, HCO₃⁻ absorption↑

HCO₃⁻ secretion↑

Urine acidic



2 C.Intra cellular concentration of K⁺ isn’t plasma factor that controls the HCO₃⁻

(K⁺ administration )

K⁺ enters the cell(tubular )

H⁺ ions leave cell

H⁺ ions buffered by HCO₃⁻ H₂CO₃

Conc of HCO₃⁻↓

↓secretion H⁺ across tubular epithelial cells

↓HCO₃⁻ reabsorption

HCO₃⁻ excretion ↑ →→Urine alkaline



2d. Intracellular Concentration of K⁺is not a plasma factor that controls the HCO₃⁻

(K⁺ deficiency )

K⁺ leaves the cell(tubular )

H⁺ ions renter tubular cell

H⁺ ions secretion↑

Excretion of NaH₂PO₄,NH₄Cl↑

↑secretion H⁺ across tubular epithelial cells

HCO₃⁻ reabsorption↑

HCO₃⁻ excretion ↓ →→Urine acidic- paradoxic aciduria



2. Intracellular Concentration of K⁺ isn’t a plasma factor that controls the HCO₃⁻

K⁺Conc↑ ECF acidic Urine alkaline

K⁺Conc↓ ECF alkaline Urine acidic

↑HCO ₃⁻ absorption

↓HCO ₃⁻ absorption, ↑HCO ₃⁻excretion



3a. Plasma Concentration of Cl⁻

Plasma Cl⁻↑

HCO₃⁻ reabsorption↓

HCO₃⁻ excretion ↑



3b. Plasma Concentration of Cl⁻

Plasma Cl⁻↓

HCO₃⁻ reabsorption↑

HCO₃⁻ excretion ↓



4. Concentration of adrenal corticoid Hormones

Cushing syndrome K⁺ deficiency HCO₃⁻reabsorption

Reabsorption of bicarbonate ions in renal tubular cells : Summary

Bicarbonate mechanismof proximal renal tubularcells for acid base

balance : summary

Phosphate buffer mechanism ( Distal tubular cells )for acid base balance

Ratio :Na₂ HPO₄ : NaH₂PO₄ 4:1 ( Plasma )

Ratio :Na₂ HPO₄ : NaH₂PO₄1:9 ( urine )

H⁺ ↔ NaHCO₃⁻ ( reabsorbed completely )

H⁺ ↔ Na₂HPO₄

H⁺ Na⁺

Na₂ HPO₄ NaH₂PO₄ (urine acidic )


Blood Distal tubular cells Tubular filtrate 7.4

Na ₂HPO₄

Carbonic Anhydrase*

CO₂ ------------------------- CO₂ -------------------- H₂ CO₃ 2Na⁺ + HPO₄⁻

H₂O--------------------------------------H₂O ↗

↙ HCO₃ ⁻←------------ -------- HCO₃ ⁻ H ⁺--------------------- H⁺

NaHCO ₃

↖Na ⁺←-------←← ---------------------------Na ⁺←---------------------Na ⁺

Na ⁺ pump ( passive transport )

( active transport ) Na ⁺+ H⁺+ HPO₄⁻

NaH₂PO₄

Phosphate buffer mechanism( Distal tubular cells )for acid base balance



Anion Gap= AG

Anion Gap =Unmeasured Anion(A)- unmeasured cation ( C ) = - (C )=AG

( Cl⁻ + HCO³⁻) –( Na⁺ + K ⁺) =0

( Cl⁻ + HCO³⁻ + PO₄⁻²+ SO₄⁻²) -( Na⁺ + K ⁺+ Li + Mg²⁺)

24 mmol/lt 7 mmol/lt

Unmeasured anion

Anion Gap= AG = 17 mmol/lt

Anion Gap increases when Unmeasured Anion (A) ↑

HA H⁺ + A⁻ (H⁺ buffered ) therefore A⁻ ↑

Anion Gap= AG

Negative Anion Gap

Anion Gap

Anion Gap in Metabolic acidosis

Anion Gap in Metabolic acidosis ( acid accumulation and bicarbonate ion loss )

Urinary anion gap: indicator of effective renal acid secretion during acidosis

I Clinical Conditions associated with increase in Anion Gap

• Anion Gap increases ( Lactate ,Acetoacetate ↑ )

I Condition associated with increase in Anion Gap

a) Diabetes Mellitus

b) Starvation

c) Lactic acidosis

d) ↑Plasma protein –dehydration

e) Toxin in gestation (Methanol, Salicylates )

• Acidosis HCO₃ absorption ,Anion gap ↑

• Excretion of K ⁺ ↑ ,Cation ↓

• Therefore ( A ) – ( C ) = AG ↑

II Clinical Conditions associated with increase in Anion Gap

II Condition associated with increase in Anion Gap

a) Metabolic alkalosis ( occasional )

b) Filtration of plasma proteins ( loss of H ⁺ )

c) Loss of H ⁺ negativity charge proteins ↑

Comparison of Anion Gap ibetween Metabolic acidosisAnd Metabolic alkalosis

Conditions associated with decrease in Anion Gap ( Anions ↓,Cations↑ )

Conditions associated with decrease in Anion Gap ( Anion ↓,Cation↑ )

↓UNMEASURED ANIONS(unmeasured)

(A)Hypo albuminemia

(B) Hypo natraemia

↑UNMEASURED ANIONS(unmeasured)

(A) Lithium intoxication

(B) Hypomagnesaemia

( C) Multiple myeloma

γ-Immunoglobins carry positive charge

Ammonia mechanism in kidney-Distal tubular cells for acid base balance

Ammonia mechanism in kidney-(Distal tubular cells) for acid base balance –Glutaminase

Ammonia mechanism in kidney-(Distal tubular cells )for acid base balance

Functions of Distal tubular cells

1. Elimination of H⁺ ions

2. Conservation of sodium

Sources of AMMONIA in Distal tubular cells

A. Hydrolysis of Glutamine

H₂O

Glutamine ---------------------------- Glutamic acid + NH₃

Glutaminase

B. Oxidative deamination of L amino acids

Ammonia mechanism in kidney-Distal tubular cells for acid base balance-

B. Oxidative deamination of L- amino acids by L- amino acid oxidase

Ammonia mechanism in kidney-(Distal tubular cells ) for acid base balance-L-amino acid oxidase

Ammonia mechanism in kidney(Distal tubular cells )for acid base balance- Glycine oxidase

C : Glycine oxidase

Metabolic acidosis

• 1. Primary HCO₃⁻ deficit ↓

• 2.Ratio BHCO₃:H₂CO₃ < 20:1↓ (as BHCO₃deficit↓)

• 3. p H ↓

Respiratory acidosis

• Primary H₂CO₃ excess↑

• 2.Ratio BHCO₃:H₂CO₃ < 20:1↓ (as H₂CO₃ excess↑)

• 3. p H ↓

Metabolic alkalosis

• 1.Primary HCO₃⁻ excess ↑

• 2.Ratio BHCO₃:H₂CO₃ > 20:1 ↑(as BHCO₃ excess↑)

• 3. p H↑

Respiratory alkalosis

• Primary H₂CO₃ deficit↓

• 2.Ratio BHCO₃:H₂CO₃ > 20:1↑ (as H₂CO₃ deficit↓)

• 3. p H ↑

Comparison between different types of acidosis & alkalosis


Metabolic acidosis

• 1. Primary HCO₃⁻ deficit ↓

• 2.H₂CO₃ ↓

• 3.Ratio↓

• 4. p H ↓

• 5.P CO₂ ↓

• 6. TotalCO₂ ↓


• 1.Primary H₂CO₃ excess↑

• 2.HCO₃⁻↑

• 3. Ratio ↓

• 4. p H ↓

• 5. P CO₂↑

• 6. Total CO₂↑

Metabolic alkalosis

• 1.Primary HCO₃⁻ excess ↑

• 2. H₂CO₃↑

• 3.Ratio↑

• 4. p H↑

• 5. P CO₂↑

• 6. TotalCO₂↑


• Primary H₂CO₃deficit↓

• 2. H₂CO₃ ↓

• 3.Ratio↑

• 4. p H ↑

• 5.P CO₂ ↓

• 6. TotalCO₂ ↓

Uncompensated phase of acid base imbalance


Metabolic acidosis

• 1. Primary mechanism-Respiratory

• 2.p H ↓

• 3.Respiratory centreStimulated ↑

• 4.CO₂ released

• 5.PlasmaH₂CO₃↓till physiological ratio value achieved


• 1.Primary mechanism- Renal

• 2.H⁺↔Na⁺↑, NH₃ Synthesis ↑

• 3. Reabsorption of HCO₃⁻↑ (renal tubular cells )

• 4. Plasma HCO₃⁻↑till physiological ratio value achieved

Metabolic alkalosis

• 1. Primary mechanism-Respiratory

• 2. p H↑

• 3. Respiratory centreinhibited

• 4. CO₂ retention↑

• 5. Plasma H₂CO₃↑ till physiological ratio value achieved


• 1.Primary mechanism-Renal

• 2. H⁺↔Na⁺↓,NH₃ Synthesis ↓

• 3. Reabsorption of HCO₃⁻↓ (renal tubular cells )

• 4. Plasma HCO₃⁻↓till physiological ratio value achieved

Compensatory phase of acid base imbalance


Metabolic acidosis

• 1. Secondary mechanism-Renal

• 2.H⁺↔Na⁺↑, NH₃ Synthesis ↑

• 3. Reabsorption of HCO₃⁻↑(renal tubular cells )


• 1.Secondary mechanism-

• 2.Lung diseases-Respiratory mechanism –fails

Metabolic alkalosis

• 1. Secondary mechanism-Renal

• 2. H⁺↔Na⁺, ↓NH₃ Synthesis ↓

• 3. Reabsorption of HCO₃⁻ ↓(renal tubular cells )


• 1Secondary mechanism-Respiratory

• 2.Lung diseases-Respiratory mechanism –fails

Compensatory phase of acid base imbalance

Metabolic acidosis

• 1. pH acidic

• 2.Excretion OF NH₄Cl ↑

• 3. Excretion OF NaH₂PO₄↑(renal tubular cells )

• 4.Titrable acidity ↑


• 1. pH acidic

• 2.Excretion OF NH₄Cl ↑

• 3. Excretion OF NaH₂PO₄↑(renal tubular cells )

• 4.Titrable acidity↑

Metabolic alkalosis

• 1. pH alkaline

• 2.Excretion OF NH₄Cl ↓

• 3. Excretion OF NaH₂PO₄↓ (renal tubular cells )

• 4.Titrable acidity ↓


• 1. pH alkaline

• 2.Excretion OF NH₄Cl ↓

• 3. Excretion of NaH₂PO₄↓(renal tubular cells )

• 4.Titrable acidity ↓

Compensatory phase of acid base imbalance-Urinary findings `

Comparison between different types of acidosis & alkalosis-Clinical conditions

Metabolic acidosis

•1. Diabetes Mellitus

•2. Starvation

•3. Lactic acidosis

•4. Violent /Heavy exercises

•5. Ingestion of acidifying salts

•6. Renal insufficiency retention of acids

•7. Loss of HC0₃⁻ ( as diarrhea , fistula )


•1. Damage of CNS

•2.Brain damage

•3. Drug poisoning 4.anesthesia excess

•5. Obstruction to escape of CO₂

•6. IMPAIRED DIFFUSION-

•a.Pneumonia

•b.Pulmonary edema

•c.Fibrosis

•d.Emphysema

•e.Reduction of respiratory surface

•7. Blood flow ↓congenital heart diseases

•8.Loss of ventilation function( as thorasic pressure ↑-cyst ,pulmnory cancer )

Metabolic alkalosis

•1.Excess loss of HCL

•2.Pyrolic obstruction

•3..intestinal obstruction

•4 pylori spasm

•5.Alkali ingestion

•X-ray irradiation

•K⁺ loss K ⁺deficiency


•1. Stimulation of respiratory center

•2.CNS diseases –Meningitis ,Salicylates

•3.. Hysteria

•4.High altitude

•5.Unjudious use of respirator

•6.Hepatic coma

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Health & Medicine

Biochemical mechanismsof acid base balance and acid base disorders