The Role of Hydrogen Ions in the Body
Hydrogen ion concentration is not just a laboratory marker, but a key factor in maintaining homeostasis (or homeokinesis) in cells and biological fluids. The correct functioning of the entire organism depends on how stable this parameter is. Hydrogen ions directly interfere with the kinetics of enzymatic reactions, accelerating or slowing them down. They determine the physicochemical and structural state of cell membranes, and also influence macromolecule conformation, which is critical for protein structures.
In addition, the proton level regulates the oxygen affinity of hemoglobin, determining the efficiency of tissue respiration. It also controls the intensity of processes involving reactive oxygen species and lipid peroxidation. Finally, excitability and conductivity of neural structures depend on the hydrogen index. Any deviations from the norm inevitably lead to metabolic disorders, severe dysfunction, and ultimately the death of cells, tissues, and the entire organism.
Clinical Significance of pH Shifts
In clinical practice, the acid-base balance is always assessed by the pH value. The human body has an extremely narrow range of permissible values for this parameter, and going beyond it is accompanied by a predictable and very severe clinical picture.
- Shift by ±0.1: triggers initial pathological processes manifested by respiratory and circulatory disorders.
- Shift by ±0.3: makes the patient's condition critical. Loss of consciousness occurs, and deep hemodynamic and pulmonary ventilation disorders develop.
- Shift by ±0.4 and more: is considered fatal. Such changes are incompatible with the normal course of biochemical reactions and lead to the death of the organism.
Main ABB Parameters
For accurate diagnosis of disorders in clinical practice, a set of main parameters is used. They allow the physician to assess the degree of compensation and the nature of the shift. Normal values depend on the type of blood tested and the selected units of measurement.
| Parameter | Definition | Norm (SI) | Traditional units |
|---|---|---|---|
| Arterial blood pH | Hydrogen index | 7,37–7,45 | — |
| Venous blood pH | Hydrogen index | 7,34–7,43 | — |
| Capillary blood pH | Hydrogen index | 7,35–7,45 | — |
| pCO₂ | Partial pressure of carbon dioxide | 4.3–6.0 kPa | 33–46 mmHg |
| SB | Standard Bicarbonate | 22–26 mmol/L | — |
| BB | Buffer Base (capillary blood buffer bases) | 44–53 mmol/L | — |
| BE | Base Excess (capillary blood base excess) | –3.4...2.5 mmol/L | — |
These parameters form the baseline profile relied upon by the physician when making a diagnosis. The evaluation is carried out strictly taking into account the normal range of each of the listed markers.
Additional Parameters
In addition to the baseline profile, there are additional parameters. Their main clinical task is to help determine the specific cause and detailed mechanism of development of non-respiratory forms of acid-base balance disorders. To this end, two types of biological fluids are examined: blood and 24-hour urine.
Blood test: The concentration of specific metabolites is determined in the blood. The level of ketone bodies (KB) should normally range from 0.5 to 2.5 mg% (in traditional units). The lactic acid (LA) content in a healthy organism is maintained within the range of 6–16 mg%.
24-hour urine test: Renal compensation is assessed by two key parameters. The first is titratable acidity (TA), the normal value of which in the SI system is 20–40 mmol/L. The second important marker is ammonia. Its excretion is normally 10–107 mmol/day, which translates to a concentration of 20–50 mmol/L.
Briefly: answers to topical questions
What types of non-respiratory acidosis exist?
Non-respiratory acid-base balance disorders, according to their causes and mechanisms of development, include the following types:
- Metabolic;
- Excretory — renal, gastric, intestinal;
- Exogenous acidoses — associated with the introduction of substances with acidic properties into the body;
- Mixed — combined forms of disorders.
What are the mechanisms of renal compensation in acid-base balance disorders?
Renal mechanisms of compensation belong to long-term mechanisms of acid-base balance correction. The main mechanisms for reducing or eliminating ABB shifts in nephrons include:
- Acidogenesis — energy-dependent secretion of hydrogen ions into the tubular lumen in exchange for reabsorbed sodium;
- Ammoniogenesis — formation of NH4+ and proton excretion; in renal excretory acidosis, this mechanism is ineffective due to parenchymal damage;
- Phosphate secretion — increased secretion of titratable acids in the form of NaH2PO4;
- K+, Na+-exchange mechanism — increased Na+ reabsorption coupled with H+ and K+ secretion.
In metabolic alkalosis, renal compensation also includes enhanced excretion of excess HCO3-.
Which blood buffer systems are involved in maintaining pH?
Chemical blood buffer systems represent the first mobile and effective compensation system. The following buffers function in the blood:
- Bicarbonate — consists of carbonic acid and bicarbonates, is the main plasma system;
- Hemoglobin — provides 75% of the blood buffer capacity, located only in erythrocytes (includes reduced and oxidized hemoglobin);
- Protein — located predominantly in plasma, its action is based on the amphoteric nature of proteins;
- Phosphate — includes salts of mono- and disubstituted phosphates, plays a minor role directly in the blood.
It is easy to remember the capillary blood pH norm: it is the range of 7.35–7.45. Note that the partial pressure of carbon dioxide (pCO₂) in traditional units has very similar figures — 33–46 mmHg, which visually echoes the tenths and hundredths of the hydrogen index.
Class and exam questions
What is the main parameter used to assess acid-base balance?
The fundamental criterion for assessing acid-base balance is the pH value, which reflects the concentration of hydrogen ions in biological fluids.
Which parameters are considered primary in acid-base analysis?
In clinical practice, evaluation is based on pH, partial pressure of carbon dioxide (pCO₂), standard plasma bicarbonate (SB), as well as buffer base (BB) and base excess (BE) of capillary blood.
Why are additional acid-base parameters necessary?
The levels of ketone bodies and lactic acid in the blood, as well as ammonia and titratable acidity of urine, are necessary to determine the causes and pathogenetic mechanisms of non-respiratory forms of balance disorders.
What happens when blood pH shifts by 0.3?
Such a deviation causes loss of consciousness and leads to pronounced hemodynamic and pulmonary ventilation disorders.
What else to study on this topic
- Effect of hydrogen ion concentration on macromolecular conformation
- Relationship between acid-base balance and lipid peroxidation processes
- Mechanisms of hemoglobin-oxygen affinity changes during pH shifts
- Pathogenesis of non-respiratory forms of acid-base balance disorders
- Role of the kidneys in the regulation of ammonia levels and titratable acidity
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