General characteristics and classification
Maintaining a stable pH in the body's fluid media is ensured by a set of interrelated buffer systems. They are located in the blood (plasma and erythrocytes), as well as in the intercellular spaces and cells of various tissues.
Functionally, all these mechanisms are divided into two large groups:
- Bicarbonate (hydrogencarbonate) system;
- Non-bicarbonate system, uniting the hemoglobin, protein, and phosphate buffers.
Every day, a huge volume of acidic products is generated in the body, equivalent to several liters of concentrated hydrochloric acid. However, thanks to the coordinated action of the buffers, blood acidity is kept within strict physiological limits.
Distribution of buffers in blood
The components of the buffer systems are unevenly distributed between the liquid part of the blood and formed elements—erythrocytes:
| Blood environment | Predominant buffer systems |
|---|---|
| Blood plasma | Hydrogencarbonate, protein, phosphate (the role of the latter is negligible) |
| Erythrocytes | Hemoglobin, hydrogencarbonate, as well as traces of organic phosphates |
This division allows for the efficient redistribution of ions and the neutralization of metabolites both during the passage of blood through tissues and in the lungs.
Hemoglobin buffer system
This mechanism constitutes one-third of the total blood capacity and is second in potency after the hydrogencarbonate buffer. The buffer capacity for acid here is higher than for alkali.
System composition:
- Weak acids: hemoglobin (H-Hb) and oxyhemoglobin (HHbO₂);
- Potassium salts of these acids (K-Hb and K-HbO₂).
Interestingly, oxyhemoglobin behaves as a stronger acid compared to regular hemoglobin. Hemoglobin molecules actively capture excess hydrogen protons during medium acidification, returning pH values to normal. The system functions directly inside erythrocytes and plays a key role in respiration processes.
Balance disorders: acidosis and alkalosis
When buffer mechanisms are depleted or subjected to excessive load, a shift in blood pH occurs, leading to pathological conditions:
- Acidosis (shift toward the acidic side) develops against the background of starvation, diabetes mellitus, shock states, severe renal failure, pulmonary pathologies (including pneumonia and pulmonary edema), as well as with an overdose of certain medications.
- Alkalosis (shift toward the alkaline side) occurs during incessant vomiting, intestinal obstruction, and febrile conditions.
To correct severe acidosis, intravenous administration of sodium hydrogencarbonate is used, whereas for alkalosis, ascorbic acid solutions are used.
Mnemonic: Main Heads Form Buffers (Hydrogencarbonate, Hemoglobin, Phosphate, Protein).
Class and exam questions
Which buffer systems predominate in blood plasma?
In blood plasma, the hydrogencarbonate and protein buffers play the main role. The phosphate buffer is present in plasma, but its role is negligible.
Which buffer system is the second most potent in the blood?
The second most potent buffer after the hydrogencarbonate buffer is the hemoglobin system, which accounts for about one-third of the total blood buffer capacity.
How do the causes of acidosis and alkalosis differ?
Acidosis is triggered by diabetes mellitus, starvation, shock, renal failure, and lung diseases. Alkalosis is more commonly associated with vomiting, intestinal obstruction, and fever.
What else to study on this topic
- Mechanisms of action of the hydrogencarbonate buffer in plasma
- The role of plasma proteins in maintaining acid-base balance
- The significance of the phosphate buffer system in cells and urine
- The relationship between the respiratory system and blood buffer mechanisms
- Dissociation constants of hemoglobin and oxyhemoglobin (pKₐ)
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