Chapter 11: Acid-Base Balance During Exercise Flashcards
3 factors that H+ production depends on
1) exercise intensity
2) amount of muscle mass involved
3) duration of exercise
how does the decline in blood pH compare to the decline in muscle pH?
muscle pH declines more dramatically than blood pH
3 source of H+ ions during exercise
1) production of CO2
2) production of lactic acid
3) ATP breakdown
where does carbon dioxide come from?
end product of oxidative phosphorylation (bicarbonate buffering reaction contributes the H+ ions with an increase in CO2)
where does lactic acid come from?
glucose metabolism via glycolysis; lactic acid <—> lactate + H+
how does ATP production result in H+ increase?
ATP + H2O <—> ADP + HPO4- + H+
what types of sports/exercises promote acid-base disturbances in skeletal muscle?
higher intensity exercises lasting greater than 45 seconds (linked to effort/max effort)
2 ways increased [H+] impairs performance
1) inhibits enzymes in aerobic and anaerobic ATP production
2) [H+] can impair muscle contraction by competing with Ca2+ for binding sites on troponin
how is the acid-base balance maintained during exercise?
by buffers that releases H+ ions when pH is too high and accepts H+ ions when pH is too low
5 cellular buffer systems (first line of defense against pH changes)
1) bicarbonate *
2) phosphates *
3) proteins
4) carnosine
5) transport of hydrogen ions out of muscle
which have a higher buffering capacity: type I or type II?
type II muscle fibers have a higher buffering capacity
how does high intensity exercise training improve the muscle buffering capacity?
by increasing carnosine and hydrogen ion transporters in the trained muscle fibers
2 blood buffer systems (second line of defense against changes in pH)
1) respiratory compensation for metabolic acidosis
2) bicarbonate
given the bicarb buffering equation:
CO2 + H2O <—> H2CO3 <—> H+ + HCO3-
how does decreasing pH lead to CO2 removal by lungs?
decreased pH (increased H+ ions) —> reaction moves to the left —> CO2 is removed by the lungs —> eliminating H+ and increasing pH
what is ventilatory threshold caused by?
increasing blood PCO2 and H+ (increasing K+, increasing body temp, elevated blood catecholamines and neural influences may contribute as well)
what group proves that lactic acid production does not cause the ventilatory threshold?
McArdle’s patients (they can’t produce lactic acid but they still experience a ventilatory threshold)
how does arterial PO2 change during graded exercise in an untrained subject?
maintained within 10-12 mmHg of resting value; does not change much (not experiencing exercise-induced arterial hypoxemia)
how does arterial PCO2 change during graded exercise in an untrained subject?
arterial PCO2 slightly decreases with maximal exercise (because of hyperventilation)
how does arterial pH change during graded exercise in an untrained subject?
decreases with maximal exercise (increasing H+ production causes buffering systems to reach capacity)
how does ventilation change during graded exercise in an untrained subject?
linear increase up to 50-75% VO2 max, then exponential rise
are kidneys significant in maintaining the acid-base balance during exercise? why?
no, because there is decreased blood flow to the kidneys
how do kidneys contribute to the acid-base balance at rest?
by regulating the blood bicarbonate concentration:
decreased blood pH (increased H+ ions) —> bicarbonate excretion by kidneys is reduced
increased blood pH (decreased H+ ions) —> bicarbonate excretion by kidneys is increased
3 ways lactate can be removed following exercise
1) 70% of lactic acid is oxidized by heart and skeletal muscle to make energy
2) 20% converted to glucose via Cori cycle in the liver
3) 10% converted to amino acids
what helps lactic acid removal after strenuous exercise?
lactic acid is removed more rapidly with light exercise in recovery (optimal intensity of recovery exercise is 30-40% VO2 max)
