1. Unit Five: The Body Fluids and Kidneys
Chapter 30: Acid-Base Regulation
Guyton and Hall, Textbook of Medical Physiology, 12th edition

2. Acid-Base Regulation
Hydrogen Ion Concentration is Precisely Regulated
Acid- molecules that release H+ in solution
Base- ion or molecule that can accept an H+
Alkali- formed by the combination of one or more
of the alkali metals (i.e. Na) with a highly basic
ion (i.e. OH); the base portion reacts quickly
with hydrogen ions and remove them from
solution---therefore they act as bases

3. Acid-Base Regulation
Strong Acid- one that rapidly dissociates and
releases large amounts of H+ in solution
Strong Base- one that reacts rapidly and strongly
with H+ and quickly removes them from
solution

4. Acid-Base Regulation
The normal H+ concentration is 40nEq/L
( ); therefore, the normal pH is

5. Acid-Base Regulation H+ Concentration pH ECF Arterial Blood 4.0 x 10-5
Table pH and Hydrogen Ion Concentration of Body Fluids
H+ Concentration pH
ECF
Arterial Blood
4.0 x 10-5
7.40
Venous blood
4.5 x 10-5
7.35
Interstitial Fluid
Intracellular Fluid
1 x to 4 x 10-5
Urine
3 x 10-2 to 1 x 10-5
Gastric HCl
160
0.8

6. Defending Against Changes in H+
Three primary systems regulate H+ concentration
to prevent acidosis or alkalosis
Chemical acid-base buffer systems of body fluids
(1st line of defense)
The respiratory center which regulates the
removal of CO2 and therefore H2CO3 (2nd line
of defense)
The kidneys which can excrete either acid or
alkaline urine

7. Bicarbonate Buffer System
Consists of (1) a weak acid and (2) a bicarbonate salt

8. Bicarbonate Buffer System
Fig Titration curve for bicarbonate buffer system

9. Phosphate Buffer System
Addition of a Strong Acid
Addition of a Strong Base

10. Phosphate Buffer System
Role of Phosphate Buffer
Relatively insignificant as an extracellular buffer
Important in the tubular fluids of the kidney
Phosphate becomes greatly concentrated in
the tubules
Tubular fluid usually has a considerably
lower pH than extracellular fluid
Important in intracellular fluid because of the
phosphate concentration

11. Proteins As Important Intracellular Buffers
Proteins are the most plentiful buffer due to high
concentrations inside cells
In the rbc, hemoglobin is an important buffer
Approximately 60-70% of the total chemical
buffering of body fluids is inside the cells,
and most of this comes from intracellular
proteins

12. Respiratory Regulation of Acid-Base Balance
Pulmonary Expiration of CO2 Balances Metabolic
Formation of CO2
Increasing Alveolar Ventilation Decreases
Extracellular Fluid H+ Concentration and
Raises pH

13. Fig. 30.2 Change in ECF pH caused by increased or decreased rate of alveolar
ventilation, expressed as times normal

14. Respiratory Regulation (cont.)
Increased H+ Concentration Stimulates
Alveolar Ventilation
Fig Effect of blood pH on the rate of alveolar ventilation

15. Respiratory Regulation (cont.)
Feedback Control of H+ Concentration By the
Respiratory System (Negative Feedback)
Increased H+ concentration stimulates respiration
Increased alveolar ventilation decreases H+
concentration
Efficiency of Respiratory Control of H+ Concentration- cannot return the concentration
back to normal when a disturbance outside
the respiratory system has altered the pH

16. Respiratory Regulation (cont.)
Buffering Power of the Respiratory System
a. Acts as a physiologic type of buffering system
Impairment of Lung Function Can Cause
Respiratory Acidosis

17. Renal Control of Acid-Base Balance
Secretion of H+ and Reabsorption of HCO3- By
the Renal Tubules
Reabsorption of bicarbonate in different
segments of the renal tubule

18. Renal Control of Acid-Base Balance
H+ is Secreted by Secondary Active Transport in
the Early Tubular Segments
Cellular mechanisms for (1)active secretion
of hydrogen ions into the renal tubule, (2)
tubular reabsorption of bicarbonate by
formation of carbonic acid, and (3) sodium
ion reabsorption in exchange for hydrogen
ion secretion

19. Renal Control of Acid-Base Balance
Filtered HCO3 is Reabsorbed by Interaction with
H+ in the Tubules
Each time an hydrogen ion is formed in the
tubular epithelium, an HCO3 is also formed
and released back into the blood
b. HCO3 is “titrated” against H+ in the tubules

20. Renal Control of Acid-Base Balance
Primary Active Secretion of H+ in the Intercalated
Cells of Late Distal and Collecting Tubules
Fig Primary active secretion of H ion
through the membrane of the
intercalated cells

21. Renal Control of Acid-Base Balance
Phosphate Buffer System Carries Excess H+ into
the Urine and Generates New HCO3
Fig. 30.7

22. Renal Control of Acid-Base Balance
Excretion of Excess H+ and Generation of New
HCO3 by the Ammonia Buffer System
Fig Production and secretion of
ammonium ion by the proximal
tubular cells
Fig Buffering of the hydrogen ion secretion
by ammonia in the collecting tubules

23. Quantifying Renal Acid-Base Excretion
Bicarbonate excretion is calculate as the urine
flow rate multiplied by urinary HCO3 concentration
The amount of new HCO3 contributed to the blood
at any given time is equal to the amount of H+
secreted that ends up in the tubular lumen
The rest of the non-bicarbonate, non-ammmonia
buffer excreted is measured by determining a
value known as titratable acid

24. Quantifying Renal Acid-Base Excretion
Regulation of Renal Tubular H+ Secretion
Increase H+ Secretion and
HCO3 Reabsorption
Decrease H+ Secretion and
Increase PCO2
Decrease PCO2
Increase H Decrease HCO3
Decrease H Increase HCO3
Decrease ECF volume
Increase ECF volume
Increase Angiotensin II
Decrease Angiotensin II
Increase Aldosterone
Decrease Aldosterone
Hypokalemia
Hyperkalemia

25. Renal Correction of Acidosis
Acidosis Decreases the ration of HCO3/H+
in Renal Tubular Fluid
In metabolic acidosis, an excess of H+ over
HCO3 occurs in the tubular fluid primarily
because of decreased filtration of HCO3
There is also a decrease in pH and a rise in
ECF H+ concentration

26. Renal Correction of Alkalosis
Alkalosis Increases the Ratio of HCO3/H+ in
Renal Tubular Fluid
Table Characteristics of Primary Acid-Base Disturbance pH H+
PCO2
HCO3
Normal
7.4
40 mEq/L
40 mm Hg
24 mEq/L
Respiratory
Acidosis
Alkalosis
Metabolic
The primary event is indicated by the double arrows. Respiratory acid-base disorders are initiated
By an increase or decrease in PCO2; metabolic disorders are initiated by an increase or decrease in HCO3