The state of equilibrium between proton donors and proton acceptors in the buffering system of the blood that is maintained at approximately pH 7.35 to 7.45 under normal conditions in arterial blood.

1. ACID-BASE BALANCE
BY S.M GHARIB NAWAZ JAN

2. INTRODUCTION
ACID
Any compound which forms H⁺ ions in a solution.
A proton donor.
E. g: Carbonic acid releases H⁺ ions
Strong acid: Ionizes freely, gives up most of its hydrogen ions, and can markedly
lower the pH of a solution, such as hydrochloric acid (HCl).
Weak acid: ionizes only slightly and keeps most hydrogen in a chemically bound
form that does not affect pH, such as carbonic acid (H2CO3).

3. BASE
Any compound which combines with H⁺ ions in a solution.
A proton acceptor.
E. g: Bicarbonate(HCO3⁻) accepts H+ ions.
Strong base: such as the hydroxyl ion (OH) has a strong tendency to bind H and
raise the pH. E. g Sodium hydroxide (NaOH).
Weak base: such as the bicarbonate ion (HCO3) binds less of the available H
and has less effect on pH. E. g Ammonia (NH3).

4. ACID- BASE BALANCE
The state of equilibrium between proton donors and proton acceptors in the
buffering system of the blood that is maintained at approximately pH 7.35 to 7.45
under normal conditions in arterial blood.
BUFFER:
It is any mechanism that resists changes in pH by converting a strong acid or
base to a weak one.

5. Relative
concentration
[H+]
[OH–]
Acidic Alkaline (basic)
Neutral
(a) In chemistry
pH
0 7.0 14
6.8 8.0
Venous blood Arterial blood
Death Acidosis Alkalosis
Normal
Average
pH range compatible with life
(b) In the body
7.5 7.9
6.9 7. 7.3
8.0
6.8
6.8 8.0
7.0 7.1 7.2 7.4 7.6 7.7 7.8
Death

6. ACIDOSIS AND ALKALOSIS IN THE BODY
The pH of arterial blood is normally 7.45 and the pH of venous blood is 7.35, for an
average blood pH of 7.4. The pH of venous blood is slightly lower (more acidic) than
that of arterial blood because H1 is generated by the formation of H2CO3 from CO2
picked up at the tissue capillaries.
Acidosis exists whenever blood pH falls below 7.35, whereas alkalosis occurs when
blood pH is above 7.45.

7. THREE LINES OF DEFENSE AGAINST
CHANGES IN [H+]
There are three primary systems that regulate the H+ concentration in the body fluids
to prevent acidosis or alkalosis.
1. The chemical buffer systems.
2. The respiratory mechanism.
3. The renal mechanism.

8. The Chemical Acid-Base
Buffer Systems
The body fluids, which immediately combine with acid or base to prevent
excessive changes in H+ concentration. Buffer systems do not eliminate H+ from
or add them to the body but only keep them tied up until balance can be
reestablished. The body has four buffer systems.
1. The Carbonic acid–bicarbonate (H2CO3:HCO3) buffer pair system.
2. The Phosphate buffer system.
3. The Protein buffer system.
4. The Hemoglobin buffer system.

9. The Carbonic Acid-Bicarbonate
Buffer System
The carbonic acid-bicarbonate buffer system is a solution of carbonic acid and
bicarbonate ions.
Carbonic acid (H2CO3) forms by the hydration of carbon dioxide and then
dissociates into bicarbonate (HCO3) and H+.
This is a reversible reaction. When it proceeds to the right, carbonic acid acts
as a weak acid by releasing H and lowering pH. When the reaction proceeds to the
left, bicarbonate acts as a weak base by binding H, removing the ions from
solution, and raising pH.

10. The carbonic acid–bicarbonate (H2CO3:HCO3)
buffer pair system

11. The Phosphate Buffer System
◦ The phosphate buffer system is a solution which consists of an acid phosphate salt (NaH2PO4) and a basic
phosphate salt (Na2HPO4).
◦ The following reaction can proceed to the right to liberate H and lower pH, or it can proceed to the left to
bind H and raise pH. Basically, this buffer pair can alternately switch a H+ for a Na+ as demanded by the
[H+]
Na2HPO4 + H+ ⇆ NaH2PO4 + Na+
◦ The phosphate buffer system has a stronger buffering effect than an equal amount of bicarbonate buffer.
◦ However, phosphates are much less concentrated in the ECF than bicarbonate, so they are less important in
buffering the ECF.

12. The Protein Buffer System
◦ Proteins are excellent buffers because they contain both acidic and basic groups and are
abundant in ICF.
◦ The protein buffer system accounts for about three-quarters of all chemical buffering ability
of the body fluids.
◦ Some have carboxyl (–COOH) side groups, which release H when pH begins to rise and thus
lower pH:
◦ Others have amino (–NH2) side groups, which bind H when pH falls too low, thus raising pH
toward normal:

13. The Hemoglobin Buffer System
Hemoglobin (Hb) buffers the H+ generated from metabolically produced CO2 in transit
between the tissues and the lungs. At the systemic capillary level, CO2 continuously diffuses
into the blood from the tissue cells where it is being produced.
Most H+ generated from CO2 at the tissue level becomes bound to reduced Hb.
The venous blood is only slightly more acidic than arterial blood despite the large volume of
H+ generating CO2 carried in venous blood. At the lungs, the reactions are reversed and the
resulting CO2 is exhaled.

14. The Respiratory Mechanism
◦ Respiratory systems regulate [H+] through adjustments in pulmonary
ventilation.
◦ When arterial [H+] increases in air breathers, the respiratory center is stimulated
to increase pulmonary ventilation.
With increased CO2 excretion, less H2CO3 is added to body fluids and H+
decreases
◦ When arterial [H+] decreases, ventilation is reduced and breathing is also slow.
Metabolically produced CO2 is added to the blood to increase acid
production

15. The Renal Mechanism
Excretory system is the third line of defense of acid-base balance.
◦ Both [H+] and [HCO3
–] are regulated
◦ Require hours to days to compensate

16. Hydrogen Ion Excretion
Filtration rate of H+ is very low.
H+ is secreted by primary active transport and by secondary Na+/H+ anti porters
in the proximal tubule.
Type A intercalated cells in the distal and collecting tubules are H+-
secreting, HCO3
–-reabsorbing, K+-reabsorbing cells.
◦ Active at normal pH and during acidosis.
Type B intercalated cells are HCO3
–-secreting, H+- reabsorbing, K+-
secreting cells.
◦ More active during alkalosis.

17. Renal Mechanism

18. Disorders in Acid-Base Balance
Acid-base imbalances fall into two categories.
1. Respiratory (When CO2 is increased or decreased)
Acidosis
Alkalosis
2. Metabolic (When HCO3 is increased or decreased)
Acidosis
Alkalosis

19. NORMALVALUES
PaCO2 = (35-45mmHg)
PH = (7.35-7.45)
HCO3 = (22-24mEq)

20. Respiratory Acidosis
When pH becomes lower than 7.35 and CO2 increases more than 45 mmHg it
result in respiratory acidosis.
It occurs when the rate of alveolar ventilation decreases.
Carbon dioxide accumulates in the ECF and lowers its pH.

21. Respiratory Alkalosis
When pH becomes greater than 7.35 and CO2 decreases less than 35 mmHg it
result in respiratory alkalosis.
Respiratory alkalosis results from hyperventilation, in which CO2 is eliminated
faster than it is produced.

22. Metabolic Acidosis
When pH becomes less than 7.35 and HCO3 decreases less than 22 mEq it
result in Metabolic acidosis.
It can result from increased production of organic acids, such as lactic acid in
anaerobic fermentation and ketone bodies in alcoholism and diabetes mellitus.
It can also result from the ingestion of acidic drugs such as aspirin or from the
loss of base due to chronic diarrhea.

23. Metabolic Alkalosis
When pH becomes greater than 7.45 and HCO3 increases more than 24 mEq it
result in Metabolic alkalosis.
It is rare but can result from overuse of bicarbonates (such as oral antacids and
intravenous bicarbonate solutions).
From the loss of stomach acid by chronic vomiting.

24. Renal response to acidosis:
◦ When [H+] is elevated, proximal tubular cells and Type A intercalated cells secrete more H+
◦ Filtration of HCO3
– decreases; new HCO3
– enters the plasma to buffer excess H+
Renal response to alkalosis:
◦ When [H+] is low, Type B intercalated cells increase H+ reabsorption
◦ More HCO3
– is filtered; Type B intercalated cells secrete HCO3
– into the urine

25. ANY QUESTIONS ???

26. THANK YOU
From
S.M GHARIB NAWAZ