1. Blood Buffers

2. Objectives Definition of acid, base and buffer Maintenance of H+
Buffer Systems for regulation of H+
The Henderson –Hassel Balch Equation
Acid- Base disorders : Acidosis and Alkalosis

3. Back to Basics:
An acid is a substance that increases H+ concentration, thus reducing pH.
A base is a proton acceptor ., bases decrease H+ concentrations and raise the pH.

4. Acids are produced continuously during normal metabolism, although the blood concentration of free hydrogen ion ( H+) vary between narrow limits.
The acids handled by the body daily are about 20,000 mmol of volatile and mmol of non-volatile acids.

5. Relatively constant H+ concentrations are important physiologically, as small changes in pH affect enzyme activity and thus metabolism.
The immediate defense against changing H+ concentrations is provided buffers, while excretion is regulated by adaptive responses in the lungs and kidney.

6. The changes in ECF (H+) conc. or (pH) are regulated by :
Buffers: v. rapid
temporarily
traps acids or bases
Respiratory response: rapid
gets rid of or retains
CO2
Renal response: slow
excretes of fixed acids
& retains or excretes HCO3-

7. Acid Production in the Body

8. Daily Production (mmol)
Acid
Source
Normal Fate
Daily Production (mmol)
Carbon Dioxide
(carbonic acid)
Cellular respiration
Excretion by lungs
20 000
Organic acids
Lactic acid
Ketone bodies
Anaerobic glycolysis
Fatty acid oxidation
Gluconeogenesis
Tissue oxidation
1000
Mineral acids
Sulphuric acid
Phosphoric acid
Sulphur-containing amino
acids
Organic phosphorus- containing compounds
Renal excretion 70

9. Volatile Acids:
CO2: The product of oxidation of substrate for utilization, mainly CHO and fat, is carbon dioxide.
Although CO2 is not an acid, it dissolves in H2O to form H2CO3 ,so accumulation of CO2 may lower body pH .
As CO2 is excreted through lungs it can be viewed as being volatile acid

10. CO2
H+ + HCO3- ↔ H2CO3 ↔ CO2 + H2O
Removed by lungs

11. These are of 2 types: organic and inorganic
Non Volatile Acids:
These are of 2 types:
organic and
inorganic

12. Organic acids : mainly lactic acid and ketone bodies.
Lactate is produced continuously from the anaerobic metabolism of glucose, particularly in erythrocytes( no mitochondria) and skeletal muscle (strenuous exercising)
These are converted to glucose in the liver
Ketone bodies production increases with prolonged fasting and also in diabetic ketoacidosis

13. Ketone bodies are formed of fatty acids metabolism in the liver
As organic acids are almost fully metabolized , under normal circumstances they contribute little to net acid excretion

14. Inorganic Acids:
They are two main sources, sulphur-containing amino acids and phosphorus –containing organic compounds.

15. Oxidation of sulphyhydryl groups in cysteine and methionine results in the synthesis of sulphuric acid
while hydrolysis of phosphesters produces phosphoric acid.
Inorganic acidic anion must be excreted from the body by kidney

16. Buffers
Buffers are solutions of weak acids or bases which contain both dissociated and undissociated forms.

17. Buffers
Buffers limit the change of pH that would be caused by addition of strong acid or base
Buffers act effectively at pH = pK ( also its concentration determine its efficiency

18. The conc. of H+ in blood is usually of ECF expressed as the negative logarithm10 (pH) = - log H
The pH of the ECF is
It is molar concentration is nmol/L

19. Buffers in Blood and Intracellular Fluid
The main extracelluler buffers:
Carbonic – bicarbonate system
Hb (hemoglobin)
The main intracellular buffers
Proteins (Ptn)
Phosphate buffer system

20. Buffer → H Buffer
(base) (acid)
H+ + HCO3- → H2CO3 → CO2 + H2O
H+ + HPO24 → H2 PO-4
H+ + Hb- → H.Hb
H+ + Prot- → H.Prot

21. Hemoglobin:
Plays an important role more than other proteins as a buffer due to :
Relatively high concentration
Relatively rich histidine (pk=7.0)
Role in transport of blood gases

22. Tissues CO2 O2 Erythrocyte ECF CO2 O2 + HHb CO2 + H2O + HbO2 HCO3- +H+
Carbonic anhydrase
HCO3-
HCO3- +H+
Cl -
Cl -
O2 + HHb

23. Carbonic Acid-Bicarbonate system:
High concentration
Ratio rapidly corrected by respiration
Components easily measured.

24. All the blood buffers are in equilibrium and changes in (H+) that affects one system produce corresponding changes in the others.
H2CO3/ HCO3- proved the most appropriate to be used to investigate the acid –base status

25. Back to Basics:
K: The relative strength of weak acids are expressed quantitatively as dissociation constants, that express the tendency to ionize.
pK= is the pH at which equal quantities of acid and its conjugate base exit.

26. Back to Basics:
HA ↔ H+ + A-
K =[ H+][A- ]
[HA]

27. [ H+]= K [HA]
[A-]

28. Take the log of both sides:
Log [ H+]= log K [HA]
[A-]
Multiply through by -1
-Log [ H+]= - log K -log [HA]

29. pH = pK + log [A-]
[HA]

30. The Henderson- Hasselbalch eq.
pH = pK + log [A-]
[HA]
Note: we can replace H2CO3 for 0.03 xPCO2
Where 0.03 is the solubility coefficient of CO2 and PCO2 is the partial pressure of CO2( since H2CO3 is in equilibrium with the dissolved co2

31. IF A- = HA
pH = pK + log 1 1

32. pH = pK + 0
so pK is the pH at which 50% of the acid is dissociated or it is a pH at which equal amounts of the acid and its conjugate base exist.

33. For Carbonic Acid-Bicarbonate system:
7.4 = log [HCO3-]
[H2CO3]

34. For Carbonic Acid-Bicarbonate system:
= log [HCO3-]
[H2CO3]
= log [HCO3-]

35. For Carbonic Acid-Bicarbonate system:
[HCO3-] = 20/1
[H2CO3]

36. Collection and transport of specimens:
Arterial blood specimens are the most appropriate.
Arterialized capillary blood could also be used.
It is essential for the capillary blood to flow freely with no vasoconstriction or sluggish blood
Patients must be relaxed
Blood is collected into containers that contain sufficient heparin as an anticoagulant
Specimens transferred to lab immediately better chilled on ice to avoid glycolysis

37. Disturbance of the Acid-Base Status
Acidosis :
pH < 7.4
HCO < 20/1
H2CO3-
↓ HCO3- = metabolic
↑ H2CO3- = respiratory
Alkalosis:
pH > 7.4
HCO > 20/1
H2CO3-
↑ HCO3- = metabolic
↓ H2CO3- = respiratory