Respiratory Regulation of Acid-Base Balance - Podcast Version 0:00 / 0:00 1x 0.25x 0.5x 0.75x 1x 1.25x 1.5x 1.75x 2x The acid-base balance is vital for normal bodily functions. Disruption of this equilibrium can lead to severe complications such as arrhythmias and seizures. Therefore, this balance is tightly regulated. In this article, we will look at the buffering system, responses of the respiratory system and relevant clinical conditions. Pro Feature - 3D Model You've Discovered a Pro Feature Access our 3D Model Library Explore, cut, dissect, annotate and manipulate our 3D models to visualise anatomy in a dynamic, interactive way. Learn More Buffering System Blood has the ability to be resistant to small changes in pH, a characteristic known as “buffering”. This is due to the basal levels of bicarbonate and hydrogen ions in blood. The chemical reaction is given by: By TeachMeSeries Ltd (2026) Fig 1An equation to demonstrate the buffering system. This reaction can be used to control pH. For example, in metabolically active tissues, there is an increase in hydrogen ions. These can react with bicarbonate in the red blood cells to form carbon dioxide which can then be exhaled by the lungs. The compensatory systems of the body rely on this equation. This will be discussed in more detail later. Henderson-Hasselbalch Equation The Henderson-Hasselbalch equation relates the pH to the ratio between the concentration of bicarbonate and the partial pressure of carbon dioxide. It is given by: By TeachMeSeries Ltd (2026) Fig 2The Henderson-Hassalbalch equation. This shows that the ratio between bicarbonate production and partial pressure of carbon dioxide drive the pH levels of the blood. By increasing bicarbonate levels, the pH will rise and turn more alkaline. By increasing the partial pressure of carbon dioxide, the pH of blood will fall and turn acidic. The usual range of blood pH is from 7.35 to 7.45. When pH levels drop below 7.35, it is said to be acidotic, and when pH levels rise above 7.45 it is said to be alkalotic. How is Balance Restored? When blood pH deviates from the normal range, there are two body systems which are activated to restore equilibrium. The respiratory system alters the respiratory rate, to change the concentration of carbon dioxide in the blood, whilst the urinary system changes the reabsorption or production of bicarbonate or hydrogen ions. This is known as “compensation”. Information on the response of the urinary system can be found here. Respiratory Responses There is a complex regulatory mechanism for changing the respiratory rate. Chemoreceptors detect the levels of certain molecules in the blood, and alter the respiratory rate accordingly. Peripheral chemoreceptors, in the carotid sinus and aortic arch, signal to the brain stem via cranial nerves to alter the respiratory rate. Central chemoreceptors function via a different method. When there is a rise in carbon dioxide in the blood, it can diffuse into the cerebrospinal fluid (CSF) as it is a small molecule. An enzyme called Carbonic Anhydrase can then turn carbon dioxide and water into bicarbonate and hydrogen ions. Hydrogen ions are then sensed by chemical chemoreceptors which alter the respiratory rate directly. Further information on the role of chemoreceptors can be found here. Clinical Relevance Respiratory Acidosis Respiratory acidosis is where there is an increase of carbon dioxide in the blood, the cause of which is due to a disorder in the respiratory system. Common causes include respiratory depression by opiates, disorders of the respiratory muscles such as in polio and airway obstructions such as in sleep apnoea. This overwhelms the buffering systems and causes a drop in pH. Therefore, the kidneys have to excrete more hydrogen ions (via the methods discussed previously) in addition to increasing bicarbonate reabsorption. Respiratory Alkalosis Respiratory alkalosis is associated with hyperventilation, which can occur due to hypoxaemia (eg. from high altitudes) or a pulmonary embolism. The compensatory methods for respiratory alkalosis is the opposite of respiratory acidosis. Due to the high levels of bicarbonate, hydrogen ions are reabsorbed to attempt to bring the pH down by decreasing hydrogen excretion and decreasing bicarbonate reabsorption and production. Do you think you’re ready? Take the quiz below Pro Feature - Quiz Respiratory Regulation of Acid-Base Balance Question 1 of 3 Submitting... Skip Next Rate question: You scored 0% Skipped: 0/3 More Questions Available Upgrade to TeachMePhysiology Pro Challenge yourself with over 2100 multiple-choice questions to reinforce learning Learn More Frequent questions What is the role of the buffering system in acid-base balance? The buffering system in the blood helps maintain pH stability by resisting changes in acidity or alkalinity. It primarily involves bicarbonate and hydrogen ions, which can react to regulate pH levels effectively. How does the Henderson-Hasselbalch equation relate to blood pH? The Henderson-Hasselbalch equation connects blood pH to the ratio of bicarbonate concentration and carbon dioxide partial pressure. An increase in bicarbonate raises pH, making it more alkaline, while an increase in carbon dioxide lowers pH, resulting in acidity. How does the respiratory system compensate for acid-base imbalances? The respiratory system compensates for acid-base imbalances by adjusting the respiratory rate to modify carbon dioxide levels in the blood. This response is mediated by chemoreceptors that detect changes in blood chemistry and signal the brain to alter breathing patterns. What causes respiratory acidosis and how is it managed? Respiratory acidosis occurs due to elevated carbon dioxide levels, often from respiratory disorders like sleep apnoea or respiratory muscle weakness. Management involves the kidneys excreting more hydrogen ions and increasing bicarbonate reabsorption to restore pH balance. What are the effects of hyperventilation on acid-base balance? Hyperventilation leads to respiratory alkalosis, characterised by decreased carbon dioxide levels in the blood. The body compensates by reabsorbing hydrogen ions and reducing bicarbonate production to lower pH and restore balance. Rate This Article