Body’s maintenance of acid – base balance

The body’s maintenance of the correct acid – base balance


Acids are electrolytes that ionise in water and release hydrogen ions. Electrolytes that combine with hydrogen ions are called bases.

Hydrogen ions are in the body mainly due to aerobic and anaerobic respiration. It is also formed because of the: incomplete oxidation of fatty acids, oxidation of amino acids containing sulfur and the breakdown of phosphoproteins and nucleic acids.

The amount of hydrogen ions present in the body is regulated in a number of ways:

Acid base buffer systems are found in body fluids and are chemical buffer systems such as the phosphate buffer system and the protein buffer systems.

The respiratory centre in the brain stem controls the rate and the depth of breathing – therefore helping to regulate hydrogen ion concentration. An example of this is during exercise, when the levels of carbonic acid in the blood increases. In response to this increase, the respiratory centre increases the rate and the depth of breathing, so that the lungs are able to excrete a greater amount of carbon dioxide.

In order to survive, the body requires acid – base balance. This means a ‘stable concentration of hydrogen ions in body fluids. The degree of acidity or alkalinity of a solution is commonly expressed as pH, which refers to the concentration of hydrogen ions in a solution’ (1), in this case the body fluids.

The body maintains it’s acid– base balance within a narrow range by using buffer systems. It also uses the lungs and the kidneys which help to neutralize and eliminate acids as rapidly as they are formed.

The Lungs control the balance by the amount of carbon dioxide that is exhaled during respiration. Carbon dioxide is acidic and is a by-product of the metabolism of oxygen in the blood. The brain controls the amount and the speed of carbon dioxide release. This is done through regulating the number of breaths taken during inhalation and exhalation. For example, if a person is breathing faster, it means that there is an excess of acid that has built up in the blood.

The brain also controls the amount of acid that is secreted by the kidneys. The difference between the lungs and kidneys is that the brain can make rapid changes in the acid level in the blood to control the acid-base balance, while the kidneys often take days to make changes in the amount of acid or base excreted from the body. ‘Minimization of changes in blood chemistry, acid-base balance, is accomplished by the body’s natural buffering system controlled by the brain. This system uses carbonic acid and bicarbonate ions to regulate the amount of acids and bases in the blood. Carbonic acid is created by carbon dioxide in the body’s blood. Bicarbonate ions are a weak base formed as a by-product of carbonic acid.’ (2)

So the main body systems that maintain the correct acid- base balance in the body are:

  • The bodies buffer systems

Extracellular buffers, such as the bicarbonate carbonic acid system, phosphates and plasma proteins.

Example of how balance is maintained, Phosphates:

The concentration of phosphate ions in the body is regulated by a hormone called the parathyroid hormone. This increases the concentrations of phosphate ions in extracellular fluids.

However, the most important extracellular buffer system is the plasma bicarbonate carbonic acid buffer system. The carbonic acid is regulated by the lungs and the bicarbonate (base component) is regulated by the kidneys.

Intracellular buffers include heamoglobin and organic phosphates

  • Respiratory system
  • The kidneys

They contribute to the maintenance of acid- base balance in a number of ways: they reabsorb the filtered bicarbonate, secrete hydrogen ions in the form of titratable acids and excrete ammonium ions.

The maintenance of acids and bases also depends on the excretion of acids from the lungs; Carbonic acid.



  1. Anatomy and Physiology 2009, by: Lippincot Williams and Wilkins, ED: Gale Thompson, chapter 16: fluids, electrolytes, acids and bases, page: 211
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