Transcript Chapter 11
Scott K. Powers • Edward T. Howley
Theory and Application to Fitness and Performance
SEVENTH EDITION Chapter
Acid-Base Balance During Exercise
Presentation prepared by:
Brian B. Parr, Ph.D.
University of South Carolina Aiken
Copyright ©2009 The McGraw-Hill Companies, Inc. Permission required for reproduction or display outside of classroom use.
Chapter 11
Objectives
1.
Define the terms
acid
,
base
, and
pH
.
2.
Discuss the importance of acid-base regulation to exercise performance.
3.
List principal intracellular and extracellular buffers.
4.
Explain the role of respiration in the regulation of acid-base status during exercise.
5.
Outline acid-base regulation during exercise.
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Chapter 11
Outline
Acids, Bases, and pH Hydrogen Ion Production During Exercise Importance of Acid-Base Regulation During Exercise Acid-Base Buffer Systems
Intracellular Buffers Extracellular Buffers
Respiratory Influence on Acid Base Balance Regulation of Acid-Base Balance via the Kidneys Regulation of Acid-Base Balance During Exercise Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved.
Chapter 11
Acids and Bases
Acids, Bases, and pH
• Acid – Molecule that can liberate H + • Increases H + concentration in solution – Lactic acid is a strong acid • Base – Molecule that is capable of combining with H + – Bicarbonate (HCO 3 – ) is a strong base Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved.
Chapter 11 Acids, Bases, and pH
pH
• • Expression of H + solution in solution Negative logarithm of H + concentration
pH = –log 10 [H + ]
pH of pure water
pH (pure water) = –log 10 [H + ] = 7.0
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Chapter 11 Acids, Bases, and pH
pH of Blood
• • • Normal pH = 7.4
±0.05
• Acidosis pH < 7.4
Alkalosis pH > 7.4
Abnormal pH can disrupt normal body function and affect performance Survival range: 6.8
–7.8
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Chapter 11
The pH Scale
Acids, Bases, and pH
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Figure 11.1
Chapter 11 Acids, Bases, and pH
Acidosis and Alkalosis
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Figure 11.2
Chapter 11
Clinical Applications 11.1
Acids, Bases, and pH
Conditions and Diseases That
• •
Promote Metabolic Acidosis or Alkalosis
– Gain in the amount of acid in the body – Long-term starvation • Through production of ketoacids • From fat metabolism – Uncontrolled diabetes • Diabetic ketoacidosis Metabolic alkalosis – Loss of acids from the body – Severe vomiting – Kidney disease Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved.
Chapter 11 Acids, Bases, and pH
In Summary
Acids are defined as molecules that can liberate hydrogen ions, which increases the hydrogen ion concentration of an aqueous solution.
Bases are molecules that are capable of combining with hydrogen ions.
The concentration of hydrogen ions in a solution is quantified by pH units. The pH of a solution is defined as the concentration: pH = –log [H + ]
Chapter 11 Hydrogen Ion Production During Exercise
Sources of H
+
Ions During Exercise
• Volatile acids – Carbon dioxide • End product of carbohydrate, fat, and protein metabolism
H 2 CO 3
H + + HCO 3 –
• • Fixed acids – Sulfuric acid • From metabolism of certain amino acids – Phosphoric acid • From phospholipid and nucleic acid metabolism Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved.
Organic acids
Chapter 11 Hydrogen Ion Production During Exercise
Sources of Hydrogen Ions Due to Metabolic Processes
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Figure 11.3
Chapter 11 Hydrogen Ion Production During Exercise
Popular Sports and Acid-Base Balance
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Chapter 11
A Closer Look 11.1
Hydrogen Ion Production During Exercise
Sport and Exercise-Induced Disturbances in Muscle Acid-Base
•
Balance
significant amounts of H + • • In many sports, risk of acid-base balance is related to effort of the competitor – Playing at 100% increases risk – Sprint to finish in distance event increases risk Acid-base disturbances can limit performance – Contributes to fatigue
Chapter 11 Hydrogen Ion Production During Exercise
In Summary
Metabolic acids can be subdivided into three major groups: (1) volatile acids (e.g., carbon dioxide), (2) fixed acids (e.g., sulfuric acid, phosphoric acid), and (3) organic acids (e.g., lactic acid).
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Chapter 11 Importance of Acid-Base Regulation During Exercise
Importance of Acid-Base Regulation During Exercise
• • Heavy exercise results in production of lactic acid Increased [H + ] can impair performance – Inhibits enzymes in aerobic and anaerobic ATP production – Hinders muscle contractile process by competing with Ca +2 for binding sites on troponin Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved.
Chapter 11 Importance of Acid-Base Regulation During Exercise
In Summary
Failure to maintain acid-base balance may impair performance by inhibiting metabolic pathways for the production of ATP or by interfering with the contractile process in the working muscle.
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Chapter 11 Acid-Base Buffer Systems
Acid-Base Buffer Systems
• Acid-base balance maintained by buffers – Release H + ions when pH is high – Accept H + ions when pH is low • Intracellular buffers – Proteins – Phosphate groups – Bicarbonate • Extracellular buffers – Bicarbonate Blood proteins
Chapter 11 Acid-Base Buffer Systems
Bicarbonate Buffering System
• Bicarbonate buffering system
CO 2 + H 2 O
H 2 CO 3
H + + HCO 3 –
• Henderson-Hasselbalch equation – Describes ability of bicarbonate-carbonic acid to act as buffer system
10 3 – / H 2 CO 3 )
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Chapter 11 Acid-Base Buffer Systems
Acid-Base Buffer Systems
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Chapter 11
• • •
Ingestion of Sodium Buffers and Human Performance
Some studies show improved performance with ingestion of sodium buffers – Other studies show no improvement in performance Sodium Buffers – Sodium bicarbonate and sodium citrate – Can increase time to exhaustion during high intensity exercise (80 –120% VO 2 max) Considerations for use
Chapter 11
In Summary
Acid-Base Buffer Systems
The body maintains acid-base homeostasis by buffer-control systems. A buffer resists pH change by removing hydrogen ions when the pH declines and by releasing hydrogen ions when the pH increases.
The principal intracellular buffers are proteins, phosphate groups, and bicarbonate. Primary extracellular buffers are bicarbonate, hemoglobin,
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and blood proteins.
Chapter 11 Respiratory Influence on Acid-Base Balance
Respiratory Influence on Acid Base Balance
• Carbonic acid dissociation equation
CO 2 + H 2 O
H 2 CO 3
H + + HCO 3 –
• When pH decreases, [H + ] increases – Reaction moves to the left – CO 2 is “blown off” by the lungs, raising pH Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved.
Chapter 11 Respiratory Influence on Acid-Base Balance
In Summary
Respiratory control of acid-base balance involves the regulation on blood PCO 2 . An increase in blood PCO 2 lowers pH, whereas a decrease in blood PCO 2 increases pH.
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Chapter 11
•
Balance via the Kidneys
Important in long-term acid-base balance – Not significant in acid-base balance during exercise • Regulate blood bicarbonate concentration – When blood pH decreases • Reduced rate of bicarbonate excretion – When blood pH increases • Increased rate of bicarbonate excretion Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved.
Chapter 11 Regulation of Acid-Base Balance via the Kidneys
In Summary
Although the kidneys play an important role in the long-term regulation of acid base balance, the kidneys are not significant in the regulation of acid base balance during exercise.
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Chapter 11 Regulation of Acid-Base Balance During Exercise
Regulation of Acid-Base Balance During Exercise
• Lactic acid production depends on: – Exercise intensity – Amount of muscle mass involved – Duration of exercise • Blood pH – Declines with increasing intensity exercise • Muscle pH – Declines more dramatically than blood pH • Muscle has lower buffering capacity Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved.
Chapter 11 Regulation of Acid-Base Balance During Exercise
Changes in Arterial Blood and Muscle pH During Exercise
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Figure 11.4
Chapter 11
•
Balance During Exercise
Buffering of lactic acid in the muscle – 60% through intracellular proteins – 20–30% by muscle bicarbonate – 10–20% from intracellular phosphate groups • Buffering of lactic acid in the blood – Bicarbonate is major buffer • Increases in lactic acid accompanied by decreases in bicarbonate and blood pH – Hemoglobin and blood proteins play minor role Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved.
Chapter 11 Regulation of Acid-Base Balance During Exercise
Changes in Blood Lactic Acid, HCO
3 –
, and pH During Exercise
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Figure 11.5
Chapter 11
•
Balance During Exercise
First line – Cellular buffers • Proteins, bicarbonate, and phosphate groups – Blood buffers • Bicarbonate, hemoglobin, and proteins • Second line – Respiratory compensation • Increased ventilation in response to increased H + concentration Copyright ©2009 The McGraw-Hill Companies, Inc. All Rights Reserved.
Chapter 11
Lines of Defense Against pH Change During Intense Exercise
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Figure 11.6
Chapter 11 Regulation of Acid-Base Balance During Exercise
In Summary
Figure 11.6 outlines the process of buffering exercise-induced acidosis.
The first line of defense against exercise-produced hydrogen ions is the chemical buffer systems of the intracellular compartment and the blood. These buffer systems act rapidly to convert strong acids into weak acids.
Intracellular buffering occurs with the and phosphate groups.
Chapter 11 Regulation of Acid-Base Balance During Exercise
In Summary
Blood buffering of hydrogen ions occurs through bicarbonate, hemoglobin, and blood proteins, with bicarbonate playing the most important role.
The second line of defense against pH shift during exercise is respiratory compensation for metabolic acidosis.
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Chapter 11
Study Questions
1.
Define the terms
acid
,
base
,
buffer
,
acidosis
,
alkalosis
, and
pH
. 2.
Graph the pH scale. Label the pH values that represent normal arterial and intracellular pH.
3. List and briefly describe the major groups of acids formed by the body.
4. Why is the maintenance of acid-base homeostasis important to physical performance?
5. What are the principal intracellular and extracellular buffers?
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