This presentation is clarifying how blood changes its medium from normal or neutral to either acidic or to alkaline medium depending on variable metabolic or respiratory circumstances.

1. ACID-BASE HOMEOSTASIS

2. A. Relative constancy of the
body’s pH is essential,
because metabolism requires
enzymes that operate at an
optimal pH.

3. B. Hydrogen ion
concentration is measured as
pH.

4. C. An acid can donate a
hydrogen ion, and a base can
accept a hydrogen ion.

5. D. Buffers are combinations
of salts and weak acids that
prevent major changes in pH.

7. E. Hemoglobin and
bicarbonate are the most
important blood buffers.

9. F. Intracellular buffering is
provided by proteins and
organic phosphates.

10. ACID-BASE DISTURBANCES

11. G. The first defense against a
change in blood pH is provided
by the blood buffers, but it is
the lungs and the kidneys that
must ultimately correct the
hydrogen load.

12. H. Changes in ventilation
can rapidly change PCO2 and
therefore alter pH.

14. I. Metabolic production of
fixed acids requires that the
kidneys eliminate hydrogen
ions and conserve HCO3.

15. J. Acid-base abnormalities
accompany many diseases,
and the restoration of normal
blood pH should be a
consideration in the
treatment of any disease.

16. K. Respiratory acidosis is
caused by the accumulation
of carbon dioxide, which
decreases blood pH.

17. Respiratory Acidosis
(hypoventilation)
• Head trauma which damages the
respiratory control centers
• Drugs which depress the respiratory
control centers
• Fractured ribs
• Airway obstruction

18. Respiratory Acidosis
H+ + HCO3-  H2CO3  H2O + CO2

H+ + Hb-  HHb

19. 24

20. L. Respiratory alkalosis
is caused by the loss of
carbon dioxide, which
increases blood pH.

21. Respiratory Alkalosis
(hyperventilation)
• Stimulation of the chemoreceptors by
hypoxia
• Stimulation of the intrapulmonary
receptors by lung injury or inflammation
• Excessive use of a ventilator while
anesthetized
• Psychogenic causes (pain, fear)

22. Respiratory
Alkalosis
H+ + HCO3-  H2CO3  H2O +
CO2

H+ + Hb-  HHb

23. 24

24. M. Metabolic
acidosis is caused by
the accumulation of
fixed acids or the loss
of buffer base, which
decreases blood pH.

25. Metabolic Acidosis
(Fixed Acids Increased)
• Anaerobic metabolism and lactic
acidosis
• Grain overload and increased acid
production in the rumen
• Exogenous toxins such as ethylene
glycol
• Ketone production in diabetes mellitus

26. Metabolic Acidosis
(Increased Loss of Buffer)
• Choke in cows with loss of saliva
(HCO3-)
• Diarrhea with excessive loss of HCO3-
in feces

27. Metabolic Acidosis
H+ + HCO3-  H2CO3  H2O + CO2

28. 24

29. N. Metabolic alkalosis is
caused by the excessive
elimination of hydrogen ions
or by the intake of base,
such as HCO-, which
3
increases blood pH.

30. Metabolic Alkalosis
• Excessive accumulation of HCO3-
– Iatrogenic HCO3- administration
• Excessive loss of H+
– Vomiting
– Abomasal Torsion
– Hypokalemia

31. Metabolic Alkalosis
H+ + HCO3-  H2CO3  H2O +
CO2

32. 24

33. O. Respiratory
compensations for acid-base
abnormalities occur rapidly;
renal compensations occur
over several hours.

34. NAE = net acid
excretion

35. P. Hydrogen and potassium
ions are interrelated in acid-base
homeostasis.

36. H+ and K+ Ion Inter-relationships
• 1. Hypokalemia can cause metabolic alkalosis.
• 2. More commonly, metabolic alkalosis causes
hypokalemia.
• 3. Acute changes in pH influence K+ secretion
by the DT and CD.
• 4. Metabolic acidosis also affects K+ ion
movement because H+ ions move into cells to
be buffered.

39. blood pH and Pfrom
CO2 which HCO-
3
concentration and total
buffer base are
calculated.

41. R. Over the years, a large
number of terms have been
used to explain acid-base
balance.

42. Acid-Base Derangements
Constant Pco2/Hco3 ratio
Acid/Base
Disorder
Primary
change
Compensatory
change
Respiratory
acidosis
Increase pco2 Increase Hco3
Respiratory
alkalosis
Decrease
pco2
Decrease Hco3
Metabolic acidosis DecreaseHco3 Decrease pco2
Metabolic
alkalosis
Increase
Hco3
Increase pco2

43. Basic Concepts
H+ conc. in ECF is determined
by balance between Pco2 partial pr.
and HCO3 conc. in the fluid.

44. • H+ in n eq/L =24 × Pco2/Hco3 .
• Using arterial pco2 of 40mmHg and HCO3 conc. of
24meq/L, the normal H+ in the arterial blood is
24 × (40/24) = 40neq/L
• Since nano-equivalent is a cumbersome term H+ is
routinely expressed as pH units .
• A normal H+= of 40neq/L corresponds to a pH of 7.4