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1.3.2.1. Functions of salts in solution

Buffer function. Regulate the pH

Salt solutions that have this function are called buffers or buffers. They are responsible for reducing the variations in pH where biochemical reactions take place, both intracellular and extracellular. 

Most of the vital functions of living beings require pH values ​​close to neutrality. Substances dissolved in water alter the pH, which must be kept close to 7 to be compatible with life, since a small variation can affect the activity of enzymes in metabolic reactions, since adverse effects could occur, such as protein denaturation, inhibition or alteration of reactions, etc.

In organisms, to prevent the pH of their fluids from changing abruptly, so - called buffer systems or pH buffers are present .

buffer solution is one that is formed by the dissolution of a weak acid and its corresponding conjugate base. The addition of small amounts of H+ or OH to these buffer systems does not produce pH changes in the buffer's own range, which makes it possible to buffer possible pH changes in the medium.

These systems are based on the properties of weak acids, that is, acids that do not completely dissociate, so that at a given pH range they act as acids or bases, proton donors or acceptors with little change in the pH of the half.

When there is an excess of H3O+ in the solution, the buffer acts as a base and accepts protons. When there is excess OH- , it acts as an acid and releases protons.

Among the most common buffers in living beings, we can mention the bicarbonate buffer and the phosphate buffer.

The bicarbonate buffer is common in the intercellular fluids such as blood plasma. They maintain the pH at values ​​close to 7.4 thanks to the balance between the bicarbonate ion and carbonic acid, which in turn dissociates into carbon dioxide  and water:

HCO3- + H+ ↔ H2CO3 ↔ CO2 + H2O

If the concentration of hydrogen ions in the medium increases by any chemical process, the equilibrium shifts to the right, and the excess carbon dioxide produced is removed from the body. If, on the other hand, the concentration of hydrogen ions in the environment decreases, the equilibrium shifts to the left, for which carbon dioxide is taken from the external environment.

The phosphate buffer is in the intracellular liquid, and maintains the pH around 6.86:

HPO42- + H+ ↔ H2PO4-

Regulate enzyme activity

The presence of certain ions (Fe 2+, Mn 2+, Cu 2+, Mg 2+, Zn2+ , ...), act as cofactors, activating or inhibiting biochemical reactions, associating with the reactant or enzymes.

For example, the Fe2+ ion is part of the heme group of hemoglobin and myoglobin, and the Mg2+ ion of chlorophyll.

Regulate osmotic pressure and cell volume. Maintenance of homeostasis

All biological liquid media, from the cell cytoplasm to the blood or sap, passing through the interstitial plasma, are saline solutions in which osmotic or osmosis phenomena occur, which have a great impact on cell stability.

Generate electrical potentials

Dissolved salts generate electrical potentials, so that on both sides of the membranes there is a difference in electrical charges. A membrane potential is produced that exerts a force on any electrically charged molecule.

The ions found inside the cells are not the same as those in the external environment, so there are different electrical charges on both sides of the membrane. This irregular distribution of ions causes the existence of a membrane potential that exerts a force on any molecule with an electrical charge.

Physiological and biochemical functions

The intervention of certain ions is necessary to carry out many biological processes. Some of the most important are the following:

Ion

Processes in which they intervene

Na +

Maintenance of ionic and aqueous balance in the extracellular environment, transmission of nerve current .

+

Muscle contraction, regulation of cardiac activity, transmission of nerve current.

Ca +2

Blood clotting, mineralization of skeletal structures, muscle contraction, regulation of cardiac activity, synaptic transmission, activator and cofactor of some enzymes.

Mg +2

Regulator of muscle contraction and nerve current transmission, constituent of functional ribosomes , activator and cofactor of some enzymes.

Ions perform essential biological functions for life. That is why it is necessary that the ionic concentrations and the ratio between the cations are kept in a constant equilibrium. Any variation of this balance, either by default or by excess, can cause important alterations.

Thus, for an adequate nerve transmission and for correct cardiac functioning, there must be a balance between the concentrations of K+ and Ca2+ , since the excess or the defect of any of these ions prevents the performance of these physiological processes.