The pH characterizes aqueous solutions in terms of their acid or base content. It depends on the hydrogen ion concentration in the solution. In the medical field, the pH of blood mainly plays a role in the diagnosis of certain diseases.
What is the pH value?
By definition, pH represents the negative decatic logarithm of the hydrogen ion concentration. It is a dimensionless value that characterizes the aqueous solution as an acid or base. The pH value varies within the numerical range from 0 to 14. At a value of 7, the solution is neutral. Values below 7 define an acid. The lower the numerical value, the more acidic the solution. Values above 7 indicate a basic solution. The determination of the pH value only makes sense for aqueous solutions because hydrogen ions (protons) or hydronium ions (proton bound to a water molecule) only occur here. Since all chemical reactions in living systems take place in aqueous solution, the pH value plays an important role in biology. Individual organs and body areas each have an individual pH value.
Structure
The organs and humors in the human body have different pH values. For example, the pH in the blood normally ranges within the narrow limits of 7.35 to 7.45, so this is a slightly alkaline range. A buffer system ensures that the values can be kept very constant. Deviation upwards or downwards indicate pathological processes in the body. Urine is generally slightly acidic, but can also be alkaline depending on the diet. Its pH value ranges from 4.5 to 7.9. The stomach produces hydrochloric acid to digest food. Therefore, it represents the most acidic organ with a pH of 1-4. The alkaline enzymes of the pancreas, which serve the enzymatic breakdown of nutrients, neutralize the food pulp again. The skin contains a so-called acid mantle with a pH value of 5.5. Sweat is also slightly acidic with a value of 4.5 in order to have an antibacterial effect. In saliva, the pH ranges from a slightly acidic value starting at 5.5 to a slightly basic value of 7.8, depending on the diet.
Function and tasks
All metabolic processes in the human body are closely linked to the pH value. Among other things, it plays a major role in sugar metabolism (glycolysis), vascular resistance, excitation conduction, muscle activity, and oxygen binding to hemoglobin. Thus, oxygen binding to hemoglobin is better at higher pH values than at lower values. The pH in blood is determined by the concentration of carbonic acid. Thus, when there is a lot of carbon dioxide (dissolved as carbonic acid) in the blood, oxygen binding decreases due to the lower pH. Breathing off the carbon dioxide also increases the basicity of the blood again. This again leads to better oxygen uptake. This mechanism already represents a simple buffer system. Thus, if the cardiovascular and respiratory activity functions normally, the pH of the blood moves within the narrow limits indicated. The uptake of oxygen and the release of carbon dioxide are subject to a regulatory mechanism. However, if the lungs are no longer able to sufficiently exhale carbon dioxide, the blood becomes more acidic and oxygen uptake is reduced. This is why pH measurements are used to diagnose certain diseases. The organism always strives to keep the pH value stable. In addition to the respiratory buffer (through breathing), the body also has chemical buffers for blood and urine. If the body fluids become too acidic, proteins are formed that intercept excess hydrogen ions. The kidneys are also involved in maintaining pH. If the body becomes too acidic, the kidneys excrete more hydrogen ions through the urine. If the body is too alkaline, more hydrogen carbonate or bicarbonate is excreted in the urine. So if the pH is supposed to rise, the urine is acidic. If the pH is supposed to decrease, the urine will appear alkaline accordingly.
Diseases
Many diseases are associated with a deviation in pH. Therefore, pH measurements are an important part of diagnosis. As already mentioned, the pH value of the blood moves within the narrow limits between 7.35 and 7.45. Even a small deviation up or down can already lead to life-threatening disturbances of the metabolism.Below a value of 7.35 we speak of acidosis and above a value of 7.45 we speak of alkalosis. Acidosis represents an overacidification of the body. There are two causes of acute acidosis. In respiratory acidosis, lung disease, rib fractures, or other causes lead to respiratory paralysis, which causes the blood to become acidic. In the less common metabolic acidosis, the acidosis is due to metabolism. Consequences of acute acidosis include low blood pressure, cardiac arrhythmias, and coma. Acute alkalosis also has a respiratory and a metabolic form. Respiratory alkalosis results from increased exhalation of carbon dioxide during hyperventilation. On the other hand, metabolic alkalosis may be caused by severe vomiting, diuretic therapy, ingestion of highly alkaline substances, or renal dysfunction. Alkalosis manifests itself in severe cardiac arrhythmias. A pH above 7.7 is fatal. The treatment of acidosis or alkalosis depends on the respective causes. Chronic diseases can also cause long-term deviation of pH.
