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Breathing Rate

Human Biology (Year 12) - Maintaining Gas Balance

Ben Whitten

What is breathing rate?

Breathing rate is varied by the body in order to  maintain a constant level of carbon dioxide and oxygen in the bloodstream.

Oxygen is required by cells for cellular respiration. If oxygen levels get too low, cellular respiration slows which as a consequence reduces the amount of energy available to the cells.

Carbon dioxide is a metabolic waste product of cellular respiration, and if allowed to get too high, cellular respiration slows reducing the amount of energy available to cells. 

(High levels of carbon dioxide decrease the body fluids pH denaturing enzymes.)

How is breathing rate controlled?

The concentration of carbon dioxide in the blood is the main stimulus for breathing rate.

High carbon dioxide concentration in the blood produces carbonic acid, which in turn breaks down into hydrogen ions and bicarbonate ions. As a result, this makes body fluids slightly acidic which therefore decreases the pH level in the body.

If blood carbon dioxide levels are high (aka, high hydrogen ion concentration, decreasing in pH levels), breathing rate increases. This occurs when exercising.

If blood carbon dioxide levels are low (aka, low hydrogen ion concentration, increasing the pH levels) breathing rate decreases. This occurs when resting.

Large variations in oxygen levels can alter breathing rates but it is not the main stimulus. Very high levels lower breathing rates, very lower levels increase breathing rates.

How do receptors help assist breathing rate?

What are the other factors affecting breathing rate?
  • Cortex area of the brain (conscious control)

  • Sudden pain or cold (increases rate)

  • Oxygen levels (must be large variations) 

  • High oxygen lowers breathing rate

  • Low oxygen increases breathing rate

  • Moving of joints and muscles (more movement means an increased breathing rate)

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