Blood pH is normally maintained within a narrow range. When pH moves outside that range, the imbalance may be metabolic or respiratory, depending on whether the primary change involves bicarbonate or carbon dioxide. This lesson introduces the four major acid-base disorders and their common causes and effects.
Normal arterial blood pH is 7.35–7.45, with a typical value near 7.40. A pH below 7.35 is called physiological acidosis; blood is not chemically acidic in the strict sense until its pH falls below 7. A sustained pH below 7.0 can be fatal. A pH above 7.45 is called alkalosis, and a pH above 7.8 can be fatal.
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What are the normal arterial blood pH range and the approximate buffer ratio at pH 7.40?
Normal arterial pH is 7.35–7.45. At approximately pH 7.40, the bicarbonate-to-carbonic-acid buffer ratio is about 20:1.
What is metabolic acidosis?
It is a low-pH disorder caused primarily by too little bicarbonate relative to acid, or by accumulation of acids in the blood.
Name three possible causes of metabolic acidosis.
Examples include diarrhea with bicarbonate loss, diabetic ketoacidosis with excess ketone bodies, and uremia with retention of acids. Strenuous exercise and some toxic substances can also contribute.
What distinguishes respiratory acidosis from respiratory alkalosis?
Respiratory acidosis results from retaining too much CO2, which increases carbonic acid. Respiratory alkalosis results from losing too much CO2 through ventilation, which reduces carbonic acid.
Why may high altitude raise blood pH?
Reduced oxygen availability can increase ventilation. Exhaling more CO2 lowers carbonic acid in the blood and may produce respiratory alkalosis.
Quiz questions
How do the lungs begin compensating for metabolic acidosis?Answer: They increase ventilation to exhale more CO2.
Why is respiratory compensation for metabolic alkalosis limited?Answer: Breathing cannot be reduced without limit to retain more CO2.
Which renal response helps compensate for respiratory acidosis?Answer: The kidneys conserve more bicarbonate and secrete more H+.
Which blood-gas pattern is most consistent with primary respiratory alkalosis?Answer: High pH with low PCO2.
What does physiological compensation do to the underlying cause of an acid-base disorder?Answer: It can move pH toward normal without necessarily removing the cause.
Based on Anatomy and Physiology 2e by J. Gordon Betts, Kelly A. Young, James A. Wise, Eddie Johnson, Brandon Poe, Dean H. Kruse, Oksana Korol, Jody E. Johnson, Mark Womble, Peter DeSaix (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.