Bicarbonate buffering system

The carbon dioxide -bicarbonate buffer system is the most important buffer for collecting blood of pH levels in the human blood stream. It is composed of the carbonic acid ( H2CO3 ) as acid, and the bicarbonate ion (also known as hydrogen carbonate ion, HCO3- ) as the base. If the blood is not acidic enough, a proton (H ) released from the carbonic acid, which is then the bicarbonate ion. If the blood contains too many protons, however, that is too acidic, the bicarbonate ion binds a proton and becomes carbonic acid. This decomposes into water (H2O) and carbon dioxide ( CO2). Through increased respiration carbon dioxide is then propagated exhaled. Conversely, the lung activity is throttled, if too little acid in the blood. Not only through respiration, and renal acid -base balance can be affected. Because they are targeted excrete able protons and bicarbonate ions or withhold in the body. Also, certain blood proteins are involved in the regulation of acid-base balance. They bind if necessary protons or release them.

Operation

The buffer system is based on the following chemical context:

Simplified, the carbonic acid ( H2CO3 ) are omitted, as their concentration in the blood by a factor of 400 less than that of carbon dioxide (CO2). It follows this equation:

For the buffer system the Henderson-Hasselbalch equation:

The pK a value for the equilibrium is 6.1 at 37 ° C.

The carbon dioxide partial pressure in the blood is approximately 40 mmHg (40 Torr), which corresponds to a concentration of 1.2 mM. At a concentration of bicarbonate ions of 24 mM, the pH value to 7.4 calculated.

Blood buffer is an open system. Here, carbon dioxide is discharged to the blood or. The partial pressure of carbon dioxide is under normal conditions at an approximately constant value held (respiratory regulation ). In addition, there is a metabolic regulation of the buffer system, so that the pH value is within about the same range. About an increased or decreased respiratory activity of the blood pH can be adjusted quickly. With an increased respiratory activity ( hyperventilation), the proportion of CO2 drops in the air, thus the partial pressure of CO2 in the lungs and in the proportion in the blood decreases. Since the law of mass action applies, CO2 is simulated from HCO3- and protons. The number of protons is reduced, characterized the pH value in the blood is increased, it becomes more basic (respiratory alkalosis). Conversely, a decreased respiratory activity ( hypoventilation ) to an increased partial pressure of CO2, then the reaction in each case run in the other direction decreases the blood pH value, it is acidic (respiratory acidosis).

However, the carbonic acid -bicarbonate system is not suitable for a permanent regulation, as with the formation of carbon dioxide and the bicarbonate ions disappear. The kidneys therefore are involved in the proton excretion and especially the recovery of hydrogen carbonate ions, however, can effectively respond to a sudden change in blood pH, after 3-4 days.