The blood pH is a measure of the acidity of the blood. It stands for "power of hydrogen" and represents the concentration of hydrogen ions, which make the blood acidic. Acidic or alkaline blood can interfere with processes in the body and be both a result of disease and a cause of further problems. Several factors are known to commonly cause acid and base disturbances in the body.
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Normal blood pH is 7.4. Lower than pH 7.4, the blood is acidic, and higher than 7.4 the blood is basic, or alkaline. Large changes in blood acidity results in small changes in the pH. In other words, even if the pH moves only a little, that small amount can represent a significant change for the amount of excess or lost acid in the blood. pH measures hydrogen by factors of ten. A pH change of 1 unit, from 7.4 to 6.4 represents a ten-times increased hydrogen ion concentration, and from 7.4 to 5.4 represents a hundred times increased concentration.
The lungs play a very important role in acid-base balance. When foods are metabolized by some biochemical pathways they are converted into the gas carbon dioxide. Carbon dioxide combines with water in the blood to make carbonic acid. When it reaches the lungs, the carbonic acid is converted back into water and carbon dioxide, and the carbon dioxide is expelled with respiration. Processes that decrease the number or volume of breaths increase carbonic acid, the acidity of the blood, and so decrease the pH. Likewise, processes that increase breathing relative to the carbonic acid production will make the blood more alkaline. Receptors in the lungs, blood vessels and brain coordinate breathing to keep the pH in an appropriate range.
Not all of the acid in the body is produced by carbon dioxide. Some acids cannot be excreted from the lungs, such as sulfuric and phosphoric acids, frequently produced by the breakdown of protein and other compounds. The kidneys are able to rid the body of these acids. They can also conserve more or less bicarbonate, which is a base. Kidney regulation of the pH can take hours to days, however, compared to seconds to minutes for respiration.
The most immediate way that pH is regulated is through buffers. A buffer solution, such as blood, resists the change of pH by essentially absorbing the acid or base that is added to it. If a small amount of acid is added to the blood, the blood will be able to neutralize the acid. Likewise, if some acid is taken away to make the blood alkaline, the blood can add a small amount of acid to counteract the effect.
High and low pH concentrations interfere with numerous body processes. Proteins perform work and chemical reactions occur in the body at normal pH. High or low pH changes the hydrogen ion concentration and interferes with these processes by changing chemical structures in cells. Symptoms depend on the cause, but may include breathing problems, malaise, distorted thinking or decreased levels of consciousness, fatigue and heart problems.
- “Physiology”; Linda S.Costanzo; 4th Ed 2008
- “Harrison’s Principles of Internal Medicine”; Anthony S Fauci et al.; 17th Ed 2008
- “Miller's Anesthesia”; Ronald D. Miller MD, Lars I. Eriksson, Lee A. Fleisher MD, and Jeanine P. Wiener-Kronish M.D.; 7th Ed 2009