Summary
Buffers, lungs and kidneys maintain blood pH between 7.35 and 7.45.
In depth
Bicarbonate buffer: CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-. Lungs adjust CO2 within minutes; kidneys excrete H+ and regenerate bicarbonate over hours to days. Acidosis and alkalosis may be respiratory or metabolic.
Respiratory compensation is fast; renal compensation is slow. Arterial blood gas tests assess status.
Key idea: pH must stay within 7.35 to 7.45 for enzymes to work.
Normal arterial pH is 7.35 to 7.45, and normal PCO2 is 35 to 45 mmHg and HCO3- is 22 to 26 mmol/L. The Henderson-Hasselbalch equation relates pH to the ratio of bicarbonate to CO2. Buffers act within seconds (bicarbonate, proteins, phosphate, haemoglobin), the respiratory system within minutes, and the kidneys within hours to days. Disorders: respiratory acidosis (hypoventilation), respiratory alkalosis (hyperventilation, altitude), metabolic acidosis (diabetic ketoacidosis, kidney failure, diarrhoea) and metabolic alkalosis (vomiting).
Compensation moves the other component in the same direction: in metabolic acidosis, deep rapid breathing (Kussmaul) lowers CO2. Blood gas analysis diagnoses these. Severe acidosis impairs enzymes and heart function.
Key idea: the body defends pH tightly because proteins are sensitive to H+ concentration.
Frequently asked questions
What is Acid-Base Balance?
Buffers, lungs and kidneys maintain blood pH between 7.35 and 7.45.
Which area of biology covers Acid-Base Balance, and how advanced is it?
Acid-Base Balance is one of the 51 topics in Human Physiology. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Blood Pressure, Altitude Physiology, Renal Autoregulation.
Can you give an example of Acid-Base Balance?
Hyperventilation causes respiratory alkalosis.
What should I learn before Acid-Base Balance?
Work through the Beginner topics in Human Physiology first, such as Homeostasis, Tissues and Organs, Skeletal System, then return to Acid-Base Balance. Advanced topics assume the Intermediate vocabulary.
What topics are related to Acid-Base Balance?
The closest topics to Acid-Base Balance are Blood Pressure, Altitude Physiology, Renal Autoregulation, Exercise Physiology. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Acid-Base Balance?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Acid-Base Balance. To practise the whole of Human Physiology, use the Human Physiology quiz.
How is Acid-Base Balance different from Blood Pressure?
Acid-Base Balance: Buffers, lungs and kidneys maintain blood pH between 7.35 and 7.45. Blood Pressure: The force of blood against vessel walls, recorded as systolic over diastolic pressure. Read both side by side and note what each one explains.
How should I study Acid-Base Balance step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Blood Pressure and explain the difference aloud. Finally, take the Human Physiology quiz and come back to this page for any question you miss.