1. Acid-base Regulation in human body
Dr. Noor-ul-ain Waheed
Assistant Professor Biochemistry
KEMU

2. Learning objectives By the end of this session you should be able to:
Descibe briefly pH of blood
Enumerate body buffer systems
Explain role of bicarbonate buffer system in human body
Discuss Four disorders of acid –base disturbance

3. 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

4. Small Changes In pH can Produce Major Disturbances
Most enzymes function only with narrow pH ranges
Acid-base balance can also affect electrolytes (Na+, K+, Cl-)

5. Major Sources of H+ in the body
Aerobic respiration of glucose
Production of CO2
Anaerobic respiration of glucose:
Production of Lactate
Fatty Acid Oxidation:
Production of ketone bodies
Sulfur containing amino acid
Production of H2SO4
Hydrolysis of phosphoproteins
Production of H3PO4

6. A Buffer system consists of
Buffer pair
(weak acid/conjugate base or salt)
When Strong acid is added
Conjugate base + Strong acid →
Salt+ Weak acid
When Strong base is added
Conjugate Acid + Strong base →
Salt + water

7. BUFFERING CAPACITY When an acid is exactly half-neutralized,
[A−] =[HA].
Under these conditions,
at half-neutralization, pH = pKa.
Equal amount of acid or conjugate base is available for neutralization
Therefore buffering capacity depends upon the pKa i.e. nearer to pH

8. DISTRIBUTION OF BUFFERS
Extra-cellular (Bicarbonate, Proteins)
Blood Buffers (Bicarbonate, Plasma Proteins, Hemoglobin, Phosphate)
Intra-cellular (Phosphate, Proteins, Bicarbonate)
Renal (Phosphate, Ammonia, Bicarbonate)

9. The Most Important Buffer System
Bicarbonate buffer system
Carbonic Anhydrase
CO2 + H2O H2CO3 H+ + HCO3-
Sites:
RBC, lung epithelium, stomach, renal tissue, intestinal tissue

10. WORKING IN STOMACH

11. Bicarbonate buffers maintains alkalinity of blood

12. Transport of carbon dioxide working with hemoglobin

13. WORKING WITH RENAL BUFFERS

17. Chemical Buffer Systems
Combination of weak acid and weak base
Binds to H+ as H+ concentration rises
Releases H+ as H+ concentration falls
Can restore normal pH almost immediately
Buffering accomplished by converting:
Strong acid  Weak acid
Strong base  Weak base

18. Bicarbonate Buffer System
The most powerful extracellular buffer in the body
Weak acid - Carbonic acid (H2CO3)
Weak base - Bicarbonate ion (HCO3-)
CO2 + H20  H2CO3  H+ + HCO3-
Works along with respiratory and urinary system (these systems remove CO2 or reabsorb HCO3- )

19. pH Derangements

21. Respiratory Acidosis
Carbonic acid excess caused by blood levels of CO2 above 45 mm Hg.
Hypercapnia – high levels of CO2 in blood
Chronic conditions:
Depression of respiratory center in brain that controls breathing rate – drugs or head trauma
Paralysis of respiratory or chest muscles
Emphysema

22. Respiratory Acidosis Acute conditons:
Adult Respiratory Distress Syndrome
Pulmonary edema
Pneumothorax

23. Compensation for Respiratory Acidosis
Kidneys eliminate hydrogen ion and retain bicarbonate ion

25. Respiratory Alkalosis
Carbonic acid deficit
pCO2 less than 35 mm Hg (hypocapnea)
Most common acid-base imbalance
Primary cause is hyperventilation

26. Respiratory Alkalosis
Conditions that stimulate respiratory center:
Oxygen deficiency at high altitudes
Pulmonary disease and Congestive heart failure – caused by hypoxia
Acute anxiety
Fever, anemia
Early salicylate intoxication

27. Compensation of Respiratory Alkalosis
Kidneys conserve hydrogen ion
Excrete bicarbonate ion

28. Metabolic Acidosis
Bicarbonate deficit - blood concentrations of bicarb drop below 22mEq/L
Causes:
Loss of bicarbonate through diarrhea or renal dysfunction
Accumulation of acids (lactic acid or ketones)
Failure of kidneys to excrete H+

29. Compensation for Metabolic Acidosis
Increased ventilation
Renal excretion of hydrogen ions if possible
K+ exchanges with excess H+ in ECF
( H+ into cells, K+ out of cells)

30. Metabolic Alkalosis
Bicarbonate excess - concentration in blood is greater than 26 mEq/L
Causes:
Excess vomiting = loss of stomach acid
Excessive use of alkaline drugs
Certain diuretics(volume contraction alkalosis)
Endocrine disorders(hyperaldosteronism)
Heavy ingestion of antacids
Severe dehydration

31. Compensation for Metabolic Alkalosis
Respiratory compensation– hypoventilation

32. Diagnosing Acid Base Disorders

33. Diagnosis of Acid-Base Imbalances
Note whether the pH is low (acidosis) or high (alkalosis)
Decide which value, pCO2 or HCO3- , is outside the normal range and could be the cause of the problem.
If the cause is a change in pCO2 the problem is respiratory.
If the cause is HCO3- the problem is metabolic.

34. THANKS