55. Chemical control of respiration. Acidosis, alkalosis

Page created on November 9, 2019. Last updated on January 24, 2022 at 16:15


Chemoreceptors are sensitive to changes in the level of certain compounds. The most important chemoreceptors are those which sense changes in pCO2, pO2 and H+. There are chemoreceptors both centrally and peripherally in the body.

When the chemoreceptors are activated, they will stimulate the respiratory centre, which will stimulate ventilation.

Central chemoreceptors:

Central chemoreceptors are located in the medulla oblongata. They’re sensitive to changes in pH ([H+]) and in pCO2. The central chemoreceptors are activated if:

  • pH decreases (acidosis)
  • pCO2 increases (hypercapnia)

Peripheral chemoreceptors:

Peripheral chemoreceptors are located in the carotid and aortic bodies. They’re sensitive to changes in pO2. The peripheral chemoreceptors are activated if pO2 decreases below 60 mmHg (hypoxia).

Acid-base disorders

Acid-base disorders like acidosis and alkalosis were described in detail in topic 21.

Respiratory acidosis:

Respiratory acidosis occurs when there is hypoventilation, i.e. breathing is not sufficient to get rid of enough CO2. This causes pCO2 to accumulate, which causes acidosis. This can occur in diseases like:

  • Chronic obstructive pulmonary disease
  • Muscle weakness involving the diaphragm

The body will compensate for the respiratory acidosis by decreasing renal HCO3 excretion.

Respiratory alkalosis:

Respiratory alkalosis occurs when there is hyperventilation, i.e. breathing is excessive compared to the body’s needs. This causes pCO2 to decrease as more CO2 is exhaled. This causes alkalosis.

Respiratory alkalosis can occur when a person voluntarily hyperventilates, or if a person is in high altitude and is not acclimatized yet.

The body will compensate by increasing renal HCO3 excretion.

4 thoughts on “55. Chemical control of respiration. Acidosis, alkalosis”

  1. Hello! Greek! I have a question ! I understand in case of respiratory acidosis , we have a lot of CO2 thats why it cause acidosis then compensation should decrease CO2 then , should it decrease HCO3- ? Rather increase it?
    But i think these process just show the processes after Respiratory insufficiency am i right?

    1. When the CO2 increases, acidosis occurs because CO2 is acidic. To compensate, we should increase the amount of base in the body. The body accomplishes this by excreting less HCO3- through the kidneys, thereby increasing the amount of base (HCO3-) in the body. However, it takes 24 hours for the kidneys to begin compensating like this.

      Like you say, in theory, it would be ideal to compensate by decreasing the amount of CO2, thereby correcting the problem, but that’s impossible. The only way the body can decrease the amount of CO2 is by hyperventilating, but that’s impossible in this case because hypoventilation is what caused the respiratory acidosis in the first place. As such, the only thing the body can do to normalise the pH is to increase the level of bases.

      I’m not sure I understand your last sentence fully, but respiratory acidosis is a result of respiratory insufficiency, yes.

      Also, in the future, I prefer to be adressed by my name rather than “Greek”.

      1. thank you and sorry at the time nikolas!!! you literally make me open my eyes !!
        i got the point but again ,, what happen in the metabolic acidosis?
        i got the point that we can’t remove enough CO2 produced in our body thats why its again “metabolic acidosis”

        1. You don’t have to apologise 🙂

          Metabolic acidosis occurs when the body produces or ingests too much acid (H+) or loses too much base (HCO3–). Metabolic acidosis is not due to being unable to remove CO2, that is respiratory acidosis. You can read more about it in topic 21.

          (I just realised that it the topic referred to topic 11 for more information about acidosis, but it’s actually topic 21. I’ve corrected it now)

          Feel free to ask further questions.

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