blood pH

See also: pH of urine; vaginal pH.

The pH of the blood, and of any other fluid, reflects the concentration of the hydrogen ions (H +) dissolved in it. A pH value of 7 is neutral; lower and upper values, on the other hand, are acid and basic.

Under normal conditions the blood is slightly alkaline, with a pH that varies within rather narrow limits, between 7.35 and 7.45. Numerous factors can influence this parameter, but the gap is still rather limited. Oscillations greater than ± 0.4 points are accompanied by severe organic impairment, and in the absence of treatment can be lethal. For this reason, the mechanisms that govern the regulation of blood pH are particularly accurate. The respiratory system, the urinary tract and the solutes of the blood buffer systems participate in this control (the first to intervene in case of "anomalies"; always present, they constitute the first line of defense).

By increasing ventilation, ie the respiratory rate and / or the depth of the breath, the body increases the amount of carbon dioxide excreted, raising the blood's pH. Vice versa in the opposite case (following blood alkalosis there is hypoventilation).

On the renal level there is another very important compensatory mechanism of blood pH, although much slower to get going. The nephrons cells can in fact respond to the acidosis by reabsorbing greater quantities of bicarbonates, secreting greater quantities of hydrogenions, reabsorbing more buffers (HCO3-) and promoting the genesis of ammonia (which has the ability to react with free H + ions forming the ion ammonium: NH3 + H + <→ NH4 +).

• THE HOMEOSTASIS OF THE EMATIC pH DEPENDS ON THE BUFFER SYSTEMS, THE LUNG AND THE KIDNEY

Acidosis and alkalosis may have a respiratory or metabolic origin. In the first case they are due to an excess or defect of carbon dioxide, while in the second they are associated with a deficit or surplus of non-volatile metabolic substances, which cannot be eliminated with the breath.

Note: carbon dioxide itself is not acidic, because it does not contain any hydrogen atom. However, in the blood environment it combines with water to form carbonic acid, which dissociates into H + and HCO3-; for the law of mass action, if the concentration of carbon dioxide increases (see figure in red), the blood environment becomes acidified. In the opposite condition (green color), the position is reversed.

Common causes of acidosis (decrease in blood pH)

Common causes of alkalosis (increase in blood pH)

Lactic acidosis (due to hypoxia or hypoperfusion, common in exercise); Ketoacidosis (massive production of ketone bodies typical of diabetes), ketosis (important production of ketone bodies typical of particularly prolonged fasting or severe malnutrition); Kidney failure; intoxication; Severe diarrhea; Hypoventilation (caused by drugs, drugs, particularly serious diseases, COPD and mildly typical even in severely obese subjects).

He retched; Excessive consumption of alkalizing agents or drugs (such as sodium bicarbonate); Hyperventilation (including that induced by drugs or artificial respirators or drugs).