Acid Base Balance
Introduction :-
Acid Base Balance- Regulation of hydrogen ion balance (H+) is similar to the regulation of other ions in the body: for example, to achieve homeostasis, there must be a balance between the uptake Or the production of H+ and the net removal of H+ from the body. And as with other ions, the kidneys play a key role in controlling the removal of H+ from the body. However, precise control of H+ concentrations in extracellular fluids requires more than simple excretion of H+ by the kidneys. Several acid-base buffering mechanisms involving blood, cells, and lungs are also important for maintaining normal H+ concentrations in extracellular and intracellular fluids. Mechanisms regulating H+ concentrations, with particular emphasis on renal H+ secretion and renal reabsorption, production and excretion of bicarbonate ion (HCO3-), one of the key components of the acid-base control system in body fluids.
Acids and Bases :-
ACID: When a free proton is released from a hydrogen ion, it becomes hydrogen atom. Molecules that contain a hydrogen atom and can release a hydrogen ion in solution are called acids. An example is hydrochloric acid (HCl), which ionizes in water to form a hydrogen ion (H+) and a chloride ion (Cl-). Similarly, carbonic acid (H2CO3) ionizes in water to form H+ and a bicarbonate ion (HCO3-).
BASE- A base is an ion or molecule that can accept H+. HCO3−, for instance, is a base since it may mix with H+ to generate H2CO3. Similarly, HPO4= is a base because it can accept H+ to form H2PO4-. Proteins in the body also act as bases because some of the amino acids that make up proteins have a net negative charge that allows them to readily absorb H+. The protein hemoglobin in proteins that are present in red blood cells and other bodily cells. body are among the most important bases in the body.
Alkalis are molecules formed by the combination of one or more alkali metals, such as sodium, potassium, or lithium, with a strongly basic ion, such as the hydroxyl ion (OH-). These molecules are typical bases because the base portion reacts rapidly with H+, removing it from solution. For similar reasons, the term alkalosis refers to the excessive removal of H+ from body fluids, as opposed to the addition of excess H+, called acidosis.
Strong and weak acid and base :-
Strong acids that dissociate quickly, such as HCl, release a significant amount of H+ into solution. Weak acids, such as H2CO3, release H+ more gently because they dissociate fewer ions. A base is considered strong if it interacts with H+ fast and vigorously, eliminating H+ from solution fast. The reaction of OH- with H+ to form water (H2O) is a common example. HCO3- is a typical weak base since it has a far weaker binding to H+ than OH-. Weak acids and bases make up the majority of the extracellular fluid acids and bases involved in regular acid-base regulation. The HCO3-base and carbonic acid (H2CO3) are the two most significant ones that will be covered.
Regulation of acid base balance- Buffer Systems :-
Buffering systems are important for maintaining the body’s acid-base balance and preventing significant pH changes in bodily fluids. These systems work by neutralizing excess acid or base, keeping the pH value stable. A weak acid (a protonated material) and a base, the salt (an unprotonated substance), combine to form an acid-base buffer system. The buffer system is the one that prevents pH fluctuations right away.
There are three types of buffer systems in body fluids that function under different conditions:
1. Bicarbonate buffer system
2. Phosphate buffer system
3. Protein buffer system.
1. Bicarbonate buffer system :-
The bicarbonate buffer system is present in the extracellular fluid (ECF) (blood plasma). It is made up of the weak acid of carbon dioxide (H2CO3), which is protonated, and the weak base HCO3–, which is unprotonated., which is a weak base. HCO3– exists in the form of a salt As sodium bicarbonate (NaHCO3).
Mechanism of action: The bicarbonate buffer system prevents the pH of a liquid from decreasing when a strong acid such as hydrochloric acid (HCl) is added. Typically, when HCl is mixed with a liquid, the pH value drops rapidly from as the strong HCl dissociates into H+ and Cl-. However, when the bicarbonate buffer system “NaHCO3” is added to a liquid along with HCl, the pH does not change significantly. This is because the H+ dissociated from the HCl combines with the HCO3- from the NaHCO3 to form weak H2CO3, which in turn dissociates into CO2 and H2O.
Normally, adding a base (NaOH) to a liquid will raise the pH. This is prevented by adding H2CO3, which dissociates into H+ and HCO3–. The hydroxyl group (OH) of NaOH combines with the H+ to form H2O, and Na+ combines with the HCO3- to form NaHCO3. NaHCO3 is a weak base and prevents the stronger NaOH from raising the pH.
Importance of the Bicarbonate Buffer System – The bicarbonate buffer system is not as powerful as other buffer systems because it is between the pH value of the extracellular fluid (7.4) and the pK value (6.1) of the bicarbonate buffer system, which are much different.But when it comes to preserving the pH of bodily fluids, one buffer system is more crucial than others. This is because the concentrations of the two components of this buffer system (HCO3- and CO2) are controlled separately by two different mechanisms. The concentration of HCO3– is regulated by the kidneys, and the concentration of CO2 is regulated by the respiratory system. These two regulatory mechanisms always work simultaneously, making this system more effective.
2. Phosphate buffer system :-
Although the phosphate buffer system is not the primary extracellular fluid buffer, it plays an important role in buffering tubular and intracellular fluids.
The potassium phosphate buffer system consists mostly of H2PO4- and HPO4-2. A combination of these two compounds reacts with a strong acid, such HCl, by accepting the hydrogen and converting it to H2PO4-.
An increased quantity of the weak acid replaces the strong acid, HCl, as a result of this interaction.
NaH2PO4, minimizing the decrease in pH.When a strong base such as NaOH is added to a buffer system, the OH- is buffered by the H2PO4-, forming an additional amount of HPO4-2 + H2O.
In this case, the strong base NaOH is exchanged for the weak base Na2HPO4, resulting in a small increase in pH.
The pK of the phosphate buffer system is 6.8, which is not far from the normal pH of body fluids, 7.4, allowing the system to operate close to its maximum buffering capacity. However, its concentration in extracellular fluids is low, only about 8% of that of the bicarbonate buffer. Thus, the overall buffering capacity of the phosphate system in extracellular fluids is much lower than that of the bicarbonate buffer system. Phosphate buffers play a crucial function in renal tubular fluids, despite their relatively small significance as an extracellular buffer. This is because they are essential for two reasons:
(1) phosphate is normally highly concentrated in the renal tubules, thereby enhancing the buffering capacity of the phosphate system.
(2) Tubular fluid typically has a significantly lower pH than extracellular fluid, bringing the
working range of the buffer closer to the pK of the system (6.8). The phosphate buffer system is also important for buffering intracellular fluid because the phosphate concentration in intracellular fluid is many times higher than in extracellular fluid. Furthermore, the pH of the intracellular fluid is normally comparable to the pK of the phosphate buffer system since it is lower than the acidic pH of the extracellular fluid. as compared to the extracellular fluid.
3. Protein buffer system.
Proteins are one of the most abundant buffers in the body, especially because they are highly concentrated in cells. Although the pH of cells is somewhat lower than that of the extracellular liquid, it varies in a manner that is approximately proportionate to variations in the extracellular fluid’s pH. There is a small amount of diffusion of H+ and HCO3- across cell membranes, but with the exception of the rapid equilibration that occurs in red blood cells, these It takes several hours for the ions and extracellular fluid to come into balance. Nevertheless, CO2 permeates all cell membranes quickly. This diffusion of elements of the bicarbonate buffer system causes the pH of the intracellular fluid to change as the extracellular pH changes. For this reason, although the buffering system within cells helps prevent changes in the pH of extracellular fluids, it may take several hours for to reach its maximum effectiveness.
Approximately 60-70% of the total chemical buffering of body fluids occurs intracellularly, and most of this buffering is produced by intracellular proteins. However, with the exception of red blood cells, the slow rate at which H+ and HCO3- pass across the cell membrane often delays the maximum ability of intracellular proteins to buffer extracellular acid-base abnormalities by several hours. In addition to the high intracellular protein concentration, another factor contributing to the buffering capacity of cells is the fact that the pKa of many of these protein systems is very close to the intracellular pH.
Regulation of acid base balance- Respiratory Mechanism :-
The lungs play a vital role in maintaining acid-base balance by removing CO2, which is produced during various metabolic activities in the body. This When this CO2 and water mix, carbonic acid is created, which is unstable and breaks down into H+ and HCO3-.
When CO2 enters the lungs, the entire reaction is reversed. diffuses from the blood into the alveoli, and ventilation expels the CO2. Increased metabolic activity produces more CO2 in the tissues, increasing the concentration of H+. The increased H+ concentration increases pulmonary ventilation (hyperventilation) by acting through chemoreceptors. Hyperventilation removes excess CO2 from the body.
Regulation of acid base balance- Renal System :-
The kidneys regulate the levels of bicarbonate ions in the blood. They affect acid-base balance by reabsorbing bicarbonate from the urine and by excreting hydrogen ions in the urine.
In response to acidosis, the kidneys may increase bicarbonate reabsorption and H+ excretion.
The kidneys may retain more H3 and reduce bicarbonate reabsorption in reaction to alkalosis.