2. Major Concepts
what are acids
what are bases
what are buffers
Regulation of PH in the Blood
Abnormalities of PH
Acidosis
Alkalosis
3. • Acids
Any compound which forms H⁺ ions in
solution (proton donors)
eg: Carbonic acid releases H⁺ ions
• Bases
Any compound which combines with H⁺
ions in solution (proton acceptors)
eg:Bicarbonate(HCO3⁻) accepts H+ ions
5. Acids and bases can be:
–Strong – dissociate completely in solution
• H2SO4, HCl
– 100% ionized (completely dissociated) in water
–Weak – dissociate only partially in solution
• Lactic acid, carbonic acid
6.
7. Weak acids
• Weak acids and bases in solution do not
fully dissociate and, create equilibrium
between the acid and its conjugate base.
• This equilibrium can be calculated and is
termed the equilibrium constant = Ka.
• The acid dissociation constant (Ka) is the
measure of the strength of an acid in
solution.
• Ka value is expressed by using the pKa, which is
equal to −log10(Ka) . The larger the value of pKa,
the smaller the extent of dissociation. the smaller
the pKa value, the stronger the acid
8. • Equilibrium
• The state of a reaction in which the rates of
the forward and reverse reactions are
equal.
• Dissociation
• Referring to the process by which a compound
breaks into its constituent ions in solution.
9.
10. Net calculation / Net equation
• HA <-----> A- + H+
• Ka = [H+][A-]/[HA]
• pKa = -logKa
11. Why is this important?
• pKa = pH -log[A-]/[HA]
• By rearranging the above equation we
arrive at the Henderson-Hasselbalch
equation:
pH = pKa + log[A-]/[HA]
13. • SOURCES OF ACIDS AND BASES IN BODY
• 50 to 100 m mol of H ions produced daily in to
15 liters of ECF
• PHOSPHORIC ACIDS
• Dietary sources , casien Phosphoprotein
• From nucleoprotein.
15. • Lactic acids
• End product of Anaerobic glycolysis
• Produced in
• RBC
• SKELTAL MUSCLES during
(EXERCISE)
• CONVERTS TO GLUCOSE IN LIVER
(gluconeogenesis)
16. • CARBONIC ACIDS (Volatile acids)
• Weak acid
• 22 MOLES / 24 HOURS
• Formed from carbondioxide and water
• CO2 + H2O H2CO3 H + + HCO3
–
• Decomposed / Removed
gaseous form from LUNGS
17. • Organic Acids
• Acetoacetate
• Beta hydroxy butyric acids
• Acetone
• Called them ketone bodies
Ktone bodies derived from Fatty acid
oxidation
DIABETES MELLITUS
18. • Non volatile acids
• Can not be decomposed or removed
from body
• Sulphuric acids
• Phosphoric acids
19. The body produces more acids than
bases
• Acids take in with foods
• Acids produced by metabolism of
lipids and proteins
• Cellular metabolism produces CO2.
• CO2 + H20 ↔ H2CO3 ↔ H+ + HCO3
-
20. pH Value
• Defined as negative log of H+ ion
concentration
• pH = - log [H+]
• H+ is really a proton
• Range is from 0 - 14
• If [H+] is high, the solution is acidic; pH
< 7
• If [H+] is low, the solution is basic or
alkaline ; pH > 7
21. What is p of pH
• Different assumptions
• Like power of hydrogen ion
• potential of hydrogen ion
• Protonated hydrogen
22. The Body and pH
• Homeostasis of pH is tightly controlled
• Extracellular fluid = 7.4
• Blood = 7.35 – 7.45
• < 6.8 or > 8.0 death occurs
• Acidosis (acidemia) below 7.35
• Alkalosis (alkalemia) above 7.45
30. Hydrogen ion (H+) Homeostasis
H+ ions are essential for life:
1. Mitochondrial function
2. Charge & shape of proteins
3. Ionisation of Ca++ & Mg++
31. Effects of Hydrogen ions
The H+ ions is extremely reactive,
positively-charged particle (Proton)
having profound effects on the functioning
of biological systems.
32. Effects of Hydrogen ions on
Enzyme systems
• Most of the enzymes function optimally over
a narrow range of H+ ions conc., close to
physiological range of pH (7.4)
• When H+ ions Conc. increases or
decreases, the metabolic functions
deteriorate due to alterations in the
structure & function of enzymes systems.
33. Effects of Hydrogen ions on
Cellular proteins
The H+ ions combine with negatively-
charged cellular proteins & cause:
• Denaturation of proteins
• Disruption of their structures
• disturbed cellular metabolism
• Death
35. Maintenance of pH
• is important for proper physiological
functioning of cells and tissues.
• Any changes in pH can alter
• Enzyme activity,
• Cellular uptake,
• incorporation and use of minerals and
metabolites,
• Uptake and release of oxygen
• formation of biological structural
components.
36. • Hydrogen Ion Regulation
• Concentration of hydrogen ions is regulated
sequentially by:
– Chemical buffer systems –
– act within seconds Chemical Buffer Systems
~ 1st to respond
~ Take < 1 sec.
~ Temporarily “tie up” excess acids & bases
– The respiratory center in the brain stem – acts
within 1-3 minutes
– Renal mechanisms – require hours to days to
effect pH changes
38. BUFFER
A buffer solution is a solution which resists
changes in pH when a small amount of acid or
base is added.
Typically a mixture of a weak acid and a salt of
its conjugate base or weak base and a salt of its
conjugate acid.
39.
40. Types of Buffers
Two types :
ACIDIC BUFFERS –
Solution of a mixture of a weak acid with a strong base
and a salt of this weak acid (conjugate base).
E.g. CH3COOH + NaOH → CH3COONa + H2O
( weak acid ) (Salt)
BASIC BUFFERS –
Solution of a mixture of a weak base with a strong acid
and a salt of this weak base (conjugate acid).
e.g. NH4OH + HCl → NH4Cl + H2O
( Weak base) (Salt)
41. How buffers work
Equilibrium between acid and base.
Example: ACETATE BUFFER
–CH3COOH CH3COO- + H+
If more H+ is added to this solution, it simply
shifts the equilibrium to the left, absorbing
H+, so the [H+] remains unchanged.
If H+ is removed , then the equilibrium shifts
to the right, releasing H+ to keep the pH constant
43. ACIDS
• VOLATILE ACIDS:
Produced by oxidative metabolism of CHO,Fat,Protein
Average 15000-20000 mmol of CO₂ per day
Excreted through LUNGS as CO₂ gas
• FIXED ACIDS (1 mEq/kg/day)
Acids that do not leave solution ,once produced they
remain in body fluids Until eliminated by KIDNEYS
Eg: Sulfuric acid ,phosphoric acid , Organic acids
Are most important fixed acids in the body
Are generated during catabolism of:
amino acids(oxidation of sulfhydryl gps of cystine,methionine)
Phospholipids(hydrolysis)
nucleic acids
44. Chemical Buffer Systems
• One or two molecules that act to resist pH
changes when strong acid or base is added.
It may be useful to think of the buffer as being
like a sponge.
• Three major chemical buffer systems
–Bicarbonate buffer system
–Phosphate buffer system
–Protein buffer system
• Any drifts in pH are resisted by the entire
chemical buffering system
49. Carbonic Acid–Bicarbonate
Buffer System
Carbon Dioxide
Most body cells constantly generate carbon dioxide
Most carbon dioxide is converted to carbonic acid,
which dissociates into H+ and a bicarbonate ion
CO2 + H2O H2CO3 H + + HCO3
–
(H2CO3 is a ‘volatile’ acid as CO2 exhaled )
51. The carbonic acid hydrogen carbonate
buffer system
• The carbonic acid-hydrogen Bicarbonate ion buffer
is the most important buffer system.
• Carbonic acid, H2CO3, acts as the weak acid
• Hydrogen carbonate, HCO3
-, acts as the conjugate
base
• Increase in H+(aq) ions is removed by HCO3
-(aq)
• The equilibrium shifts to the left and most of the
H+(aq) ions are removed
57. Phosphate Buffer System
Consists of anion H2PO4
- (a weak acid)(pKa-
6.8)
Works like the carbonic acid–bicarbonate
buffer system
• important in buffering pH of ICF & urine
• Consists of two phosphate ions
– Monohydrogenphosphate ions act as a (weak
base) and combine with hydrogen ions to form
dihydrogenphosphate (Weak acids)
– Dihydrogenphosphate dissociates to release
hydrogen ions
64. 1-The Hemoglobin Buffer System
CO2 diffuses across RBC membrane
No transport mechanism required
As carbonic acid dissociates
Bicarbonate ions diffuse into plasma
In exchange for chloride ions (chloride shift)
Hydrogen ions are buffered by hemoglobin molecules
Is the only intracellular buffer system with an immediate
effect on ECF pH
Helps prevent major changes in pH when plasma PCO
2
is
rising or falling
65.
66. • Haemoglobin binds both CO2 and H+ and so is a
powerful buffer. Deoxygenated haemoglobin has
the strongest affinity for both CO2 and H+; thus,
its buffering effect is strongest in the tissues.
• CO2 produced by the tissues passes easily into the
Redcell down a concentration gradient. Carbon
dioxide then either combines directly with
haemoglobin or combines with water to form
carbonic acid. The CO2 that binds directly with
haemoglobin combines reversibly with terminal amine
groups on the haemoglobin molecule to form
carbaminohaemoglobin. In the lungs the CO2 is
released and passes down its concentration gradient
into the alveoli.
67. 2- Plasma protein buffer system
• Consists of Plasma Proteins (albumin)
• proteins are made of Amino Acids
• The exposed amine group of the AA (NH2)
accepts H+ ions when conditions are
acidic
• The exposed carboxyl group of AA can
release H+ ions when conditions are
basic Proteins can act as Acids or Bases
Slower than other chemical buffers
68. R
NH2 – C – COOH
H
Neutral pH
• Features of an amino acid (functional
groups)
69. • If pH (more basic) [OH- ] Amino acid
acts like an acid
• If pH (more acidic) [H+]
Amino acid acts like a base
R
NH2 – C – COO- + H+
H
R
NH3
+ – C – COOH
H
70. Key Concepts: Buffers
consist of
Weak acid and
its salt
Weak base and
its salt
or
and
resist changes in pH
to
Maintain pH balance
preventing
Acidosis and Alkalosis
72. 1- Respiratory Acid-Base Control
Mechanisms
When chemical buffers alone cannot prevent
changes in blood pH, the respiratory system is
the second line of defense against changes.
Eliminate or Retain CO₂
Change in pH are RAPID
Occuring within minutes
73. • The rate of respiration (or the rate of removal
• of CO2) is controlled by a respiratory centre,
• located in the medulla of the brain.
• Respiratory centre is highly sensitive to changes
in the pH of blood.
• Any decrease in blood pH causes
hyperventilation to blow off CO2, reducing the
H2CO3 concentration.
• Simultaneously the H+ ions are eliminated as H20.
74. • Respiratory centre is highly sensitive to
changes in the pH of blood.
• Any decrease in blood pH causes
hyperventilation to blow off CO2,
reducing the H2CO3 concentration.
• Simultaneously the H+ ions are eliminated as
H20.
75. 2- Renal Acid-Base Control
Mechanisms
• The kidneys are the third line of defence
against wide changes in body fluid pH.
• 1. Excretion of H+ ions
• 2. Reabsorption of bicarbonate
• 3. Excretion of titratable acid
• 4. Excretion of ammonium ions
Long term regulator of ACID – BASE balance
May take hours to days for correction
76. Renal regulation of acid base
balance
Excretion of H+ ions
•
• kidney only route for elimination of H ions
88. CAUSES OF METABOLIC ALKALOSIS
I. Exogenous HCO3 − loads
A. Acute alkali administratio
II. Gastrointestinal origin
1. Vomiting
2. Gastric aspiration
III. Renal origin
1. Diuretics
89. Compensation for Metabolic
Alkalosis
Respiratory compensation:
HYPOVENTILATION
↑PCO₂=0.6 mm pCO2 per 1.0 mEq/L ↑HCO3
-
Maximal compensation: PCO₂ 55 – 60 mmHg
Hypoventilation not always found due to
Hyperventilation
due to pain
due to pulmonary congestion
due to hypoxemia(PO₂ < 50mmHg)
92. Compensation in Respiratory Acidosis
Acute resp.acidosis:
Mainly due to intracellular buffering(Hb,Pr,PO₄)
HCO₃⁻ ↑ = 1mmol for every 10 mmHg ↑ PCO₂
Minimal increase in HCO₃⁻
pH change = 0.008 x (40 - PaCO₂)
Chronic resp.acidosis
Renal compensation (acidification of urine &
bicarbonate retention) comes into action
HCO₃⁻ ↑= 3.5 mmol for every 10 mm Hg ↑PCO₂
pH change = 0.003 x (40 - PaCO₂)
Maximal response : 3 - 4 days
96. The Major Body Buffer Systems
Site Buffer System Comment
ISF Bicarbonate For metabolic acids
Phosphate Not important because concentration too
low
Protein Not important because concentration too
low
Blood Bicarbonate Important for metabolic acids
Haemoglobin Important for carbon dioxide
Plasma protein Minor buffer
Phosphate Concentration too low
ICF Proteins Important buffer
Phosphates Important buffer
Urine Phosphate Responsible for most of 'Titratable
Acidity'
Ammonia Important - formation of NH4
+
97.
98. Some important indicators used in a Clinical
Biochemistry Laboratory are listed below:
sr,.
No.
INDICATOR Ph range Colour in
acidic ph
Colour in
basic ph
1 Phenophthalein 9.3-10.5 colourless pink
2 Methyl orange 3.1-4.6 red yellow
3 Bromophenol blue 3.0-4.6 yellow blue
4 Methyl red 4.4-6.2 Red yellow
5 Phenol red 6.8 – 8.4 yellow red
6 Litmus 4.5-8.3 red Blue
