Lecture 27: Acid Base Balance During Exercise Flashcards
Define an ion.
An atom with one extra electron
Therefore has an electrical charge
Define an acid.
Something that can liberate hydrogen
Causes increased hydrogen in a solution
Define a base.
Something that accepts hydrogen molecules
What is pH?
The concentration of hydrogen ions
What is the survival range for pH?
6.8 –> 7.8
What are the pathological effects of a pH that is too low?
Low pH (acidosis): coma due to decreased CNS activity
What are the pathological effects of a pH that is too high?
High pH (alkalosis) spasm of respiratory muscles
What value is given for normal pH?
7.4
Why are there fewer bases with lower pH?
Because increased H+ concentration due to increased acid content (acidosis) causes more bases to combine with hydrogen
What are the three types of acid in the body? Give examples of each type and how they are produced.
Volatile Acids
CO2 + H20 –> H2CO3 –> H + HCO3 (Carbon dioxide liberates pH when combined with water)
Fixed Acids
Produced from amino acid metabolism
Sulfuric acid and Phosphoric acid
Organic Acids
Metabolism of fats and carbohydrates
Lactate
In sport, when are people most at risk of acidosis?
Sport lasting under 45 seconds
100% effort
Sprint finish
How can increased H+ (acidosis) inhibit skeletal muscle and aerobic/anaerobic performance?
H+ binds to troponin (vs. calcium) Inhibits enzymes (involved in aerobic/anaerobic pathways)
What is more acidic at maximum intensity exercise, the muscle or the arteries?
The muscle
Why does muscle pH decline more than in the arteries?
Inferior buffering capacity
What are the 3 exercising factors that determine pH production?
Duration
Intensity
Muscle mass
What is the first line of defence in regulating pH during exercise?
Cellular buffers:
Bicarbonate
Proteins
Phosphate
Blood buffers:
Bicarbonate
Proteins
Haemoglobin
What is the second line of defence against acidosis during exercise?
Increased ventilation
Give one or two constituents (e.g. carbonic acid) that act as buffers for each system.
Bicarbonate & Phosphate system:
Sodium Bicarbonate & Sodium Phosphate (strong acid –> weak acid)
Carbonic acid (weak acid –> strong acid)
Protein system:
NH3 & COO (accept H+)
What is the major buffering system in the muscle?
Proteins
What is the major buffering system in the blood?
Bicarbonate
At what exercise intensity does bicarbonate begin to decrease and lactic acid begin to increase?
Between 50% - 75%
Define a buffer.
A chemical that either liberates hydrogen during alkalosis, or removes hydrogen during acidosis
Neautral pH
What have studies shown as the effects of sodium buffers on performance?
Can increase time to fatigue at high exercise intensities
What are the drawbacks of using sodium buffers?
Can cause nausea, vomiting and alkalosis
What is the effect of increased pulmonary ventilation on pH?
Activates carbonic anylase
Converts carboxylic acid back into CO2 and water
There is a lower concentration of CO2 in the alveoli due to increased ventilation, therefore CO2 can enter lungs and be exhaled
What receptors input to the respiratory control centre?
Central chemoreceptors (medulla; PCO2 & H+; in cerebrospinal fluid) Peripheral chemoreceptors (aortic and carotid bodies; PCO2, PO2, K+, H+; in blood)
How can physiological adaptations reduce acid build up during exercise?
Delayed pH drop
Delayed ventilatory threshold
Increased buffering capacity
Which organ is the major long-term acid-base balance regulator?
The renal system
How does the renal system respond to increased acidosis?
Increases bicarbonate secretion
