A very good morning friends. Today we will discuss about an important topic for university examination and also important topic for entrance preparation that is acid-base balance. Today we will discuss about important aspects of acid-base balance or general concept of acid-base regulation.
There are some terminologies for acid-base balance. The first one is the pH. pH it is defined as it is negative logarithm of hydrogen ion concentration. That means if the hydrogen ion concentration increases pH decreases that leads to the acidosis.
The normal value is 7.35 to 7.45. If it is less than 7.35, it is acidosis. If it is more than 7.45, it is alkalosis. The pH, it is inversely related with the hydrogen ion concentration. Then next terminology that is acid.
Example is hydrochloric acid. Carbonic acid. These are the acids.
This HCl is known as strong acid while carbonic acid is known as weak acid because HCl donates proton. That's why it is known as acid and it ionizes completely. So it ionizes into H positive ion and chloride ions.
While H2CO3 it is known as weak acid because it ionizes incompletely. It dissociates into H positive and bicarbonate ions. Because of incomplete dissociation it is known as weak acid. Base.
This acid they donates protons base they accept protons. The examples are bicarbonate. and ammonia. These are the bases. They accept protons.
It is converted into carbonic acid and ammonium ions. So that's why they are known as bases. Then buffers.
Solution which resist the change in pH. Resist the change in pH. These are the solution of weak acid and its strong base. Or weak base and a strong acid. They resist the change in pH. The gram of acid or alkali required. To change the pH of one unit of one liter buffer solution is known as buffering capacity of that buffer solution.
The gram of acid or alkali which is required to change a pH of one unit of one liter buffer solution is known as buffering capacity of that solution. So pH, acid, base, buffer then alkali reserve alkali reserve means it is a bicarbonate concentration that is 24 millimole per per liter, alkali reserve. It is a bicarbonate concentration that is 24 millimole per liter.
To overcome the acids which are synthesized in our body is known as Alkali Reserve. It is 20 times higher than the acid. That's why it is known as Alkali Reserve of the body. That is bicarbonate concentration.
The normal value is 22 to 26 millimole per liter. Then pKa value, pKa value means it is a pH at which acid is half ionized. It is known as pKa value. The salts to acid ratio is 1 as to 1. It is known as the pKa.
pKa value and pKa value it is if it is nearer to the body pH that is 7.4 is the body pH if pKa value is nearer to the body pH it is most effective. So these are the some terminologies. Now coming to the Henderson-Hasselbalch equation.
This Henderson-Hasselbalch equation, they describe the relationship between pH, pKa value and concentration of base and acid. So coming to the Henderson-Hasselbalch equation. It is pH is equal to pK plus log of base divided by acid.
It describes the relationship between pH, pKa concentration of base and acid. Base it is bicarbonate HCO3. Acid or denominator it is H2CO3.
This component that is numerator it is under the control of, it is under metabolic regulation. While this carbonic acid it is under the respiratory regulation. So this numerator under metabolic regulation and denominator it is under respiratory regulation. In case of bicarbonate buffer.
The pKa of carbonic acid is 6.1 plus log of concentration of base that is 24 divided by concentration of acid that is 1.2 mmol per liter. It corresponds with the 6.1 plus log of 20. So it is 6.13. it is 7.4 so pH is pH of the body is 7.4 so this is Henderson Hasselbalch equation now coming to the Regulation of pH in the extracellular fluid or acid-base balance.
It is under the control of three important systems. The first line of defense. The first line of defense are the system which acts immediately. It is a blood buffer.
There is second line of defense but it is not a permanent mechanism in the acid-base balance. That is respiratory system. And third line of defense but it is a permanent mechanism. It is a renal mechanism.
renal mechanism. So first line of defense or the system which acts immediately after acid-base imbalance is the blood buffer. It is mainly by the bicarbonate buffer followed by the phosphate buffer followed by the protein.
Then respiratory mechanism, the two mechanism. First one is the hypoventilation and hyperventilation and second one is the hemoglobin and renal it is by the four mechanism. So we'll discuss one by one.
Coming to the blood buffer system. the blood buffer system or pH regulation via the blood buffers. The first one is the bicarbonate buffer. Second one is the phosphate buffer.
And third one is the protein buffer. These are the buffer system. In the bicarbonate buffer, it is mainly by the ratio of bicarbonate and carbonic acid, which is in the 20 is to 1. Phosphate buffer, it is mainly by the disodium acid phosphate.
and sodium dihydrogen phosphate is in the ratio of 4 is to 1 and protein it is mainly by the albumin and hemoglobin these are the important blood buffers in the extracellular fluid The pKa value of bicarbonate buffer it is 6.1 which is closer to the body pH that is 7.4. So it dissociates completely and corrects the acid base balance. The phosphate buffer it is 6.8 and protein buffer it is 6.1. It is a most important buffer in the extracellular fluid that is bicarbonate buffer because of two main reasons. The first one is because of the quantity it is present that is alkali reserve quantity and second main reason it is under physiological control.
The numerator in the Henderson-Hasselbalch equation, the numerator under metabolic regulation, while the denominator that is H2CO3 under the respiratory regulation. So it is under physiological. control.
So because of its quantity, it is most important buffer system in the extracellular fluid that is bicarbonate buffer. Then phosphate buffer, it is active at a wide range because it has three pKa value first it has three pKa value that's why it is active then the pKa value of 6.8 of this buffer system it is more closer to the physiological pH of the blood that is 7.4 that's why it is most potent buffer system in the intracellular environment that is the phosphate buffer. is MCQ in extracellular fluid most important is the bifarborate buffer in the Intracellularly, the phosphate buffer is the most important. Then in protein buffer, it is mainly due to the histidine imidazole group.
It is active. The pKa value is 6.1. So these are the three important blood buffer system which is responsible for maintenance of pH in the extracellular fluid. Now coming to the respiratory regulation which acts immediately but it is not a permanent mechanism to correct the acid-base balance that is respiratory mechanism the first respiratory mechanism There are two ways by which respiratory system acts. The first one is the hypo and hyperventilation.
And second through the hemoglobin. These are the two mechanism. If there is acidosis means if the pH is below 7.35 means acidosis.
The lungs will blow out CO2. So lungs will blow out CO2. Due to the exhalation of CO2, there is decrease in partial pressure of CO2. Which represents the dissolved carbonic acid. That is decrease in the carbonic acid.
So that corrects acidosis. Due to the hyperventilation and blowout of CO2. If pH is more than 7.45.
That is alkalosis. Means there is decrease in partial pressure of CO2. In that case, body or lung will retain CO2.
Retain CO2. That will increases the partial pressure of CO2. That means there is increase in...
in the dissolved carbonic acid level. So that will correct the alkalosis. This is the first by hypoventilation and hyperventilation.
Then through the hemoglobin, at the tissue level what happens, there is... generation of carbon dioxide at the tissue level. So suppose this is the tissue level. At tissue level what happens there is generation of CO2 which combines with the water to form carbonic acid. in presence of carbonic anhydrase.
This H2CO3 is dissociates into H positive ion and bicarbonate ion. So there is generation of bicarbonate. Then this acid which is generated here, it is neutralized by the hemoglobin.
So hemoglobin combines with the H ion to form H hemoglobin. This is at the tissue level. But at the lungs where the oxygen saturation is much more, this hemoglobin Thanks.
Combines with O2 to form hemoglobin O2 and H positive ion. Then this H positive ion combines with bicarbonate to form H2CO3. This H2CO3 dissociates into CO2 plus water molecule. So this is the two mechanism by which respiratory regulation acts or respiratory system acts by the hypo or hyperventilation and second through the hemoglobin.
Now third and permanent mechanism. or third line of defense in the acid-base balance that is the kidney or renal system or renal regulation. It is active by four mechanisms.
So renal mechanism, it is active by four. The first one is the excretion of H positive ion. Second, reclamation or recovery or reabsorption of bicarbonate. Third excretion of titrabil acids and fourth one is the Excretion of ammonium ions.
So these are the four mechanism by which kidney act. It is a third line of defense and it is a permanent mechanism for acid base regulation. The first one is the excretion of H positive ions.
So this is mainly in the proximal convoluted tubule. This is the proximal convoluted tubule. It is cell, renal tubular cell. It is tubular lumine and this is blood or extracellular fluid. Now what happens in the proximal convoluted tube with tubules that is there is formation of CO2 With the help of carbonic anhydrase there is formation of carbonic acid which dissociates into H-positive ions and bicarbonate.
So these H-positive ions exchange with the sodium ions. and this H positive ion excreted into the urine. So first mechanism is the excretion of H positive ion.
Simultaneously this sodium along with the bicarbonate absorbed into the blood. So there is Formation of bicarbonate and excretion of H positive ion means excretion of acid, conservation of bicarbonate. So this is the first mechanism by which renal system act, that is excretion of H positive ion. Now coming to the recovery or reabsorption of bicarbonate.
That is bicarbonate reabsorption or recovery. In this what happens there is this bicarbonate get filtered directly to the gromerulus into the tubular domain. domain. Ok.
This bicarbonate combines with the H positive ion to give carbonic acid which dissociates into CO2 and H2O and it gets reabsorb according to the concentration gradient. So there is no net excretion of H positive ion in the reabsorption of bicarbonate. So there is this glomerular filtrate which is into the tubular lumen in the proximal convoluted tubule.
This bicarbonate combines with the H-positive ion, lead to the generation of carbonic acid, dissociates into CO2 and H2O. And on the basis of concentration gradient, this CO2 diffuses into the proximal convoluted tubular cell, which lead to the formation of carbonic acid and bicarbonate and H-positive ion. and it into the blood. It comes into the blood with the sodium ion.
So this is the second reabsorption of bicarbonate. Now third that is titrabil acid. Excretion of titrabil acid. In this mechanism, remember for this all four mechanism, this side of diagram is same.
Only this side will change. Okay. Now, for the last two, it is in the digital convoluted two-wheel or collecting duct. What happens in the digital convoluted two-wheel?
This. directly into the lumen there is disodium acid phosphate. Now this disodium acid phosphate it is broken down and sodium hydrogen phosphate. This sodium hydrogen phosphate condenses with this H positive ion to give sodium dihydrogen phosphate and it gets excreted into a urine that is known as excretion of titanium This is the third mechanism and in the fourth mechanism that is excretion of ammonium iron in the distal converted tubule or the collecting duct, what happens?
There is synthesis of NH3 in the tubular cells that is glutamine, it is converted into glutamate. plus NH3 via glutaminase. Now this NH3 it comes into the tubular lumen combines with the H positive ion.
There is formation of ammonium ion and it get excreted in urine. So these are the four different mechanism by which renal system acts. The first one is the excretion of H ions.
Second, recovery or reabsorption of bicarbonate. Third one is the excretion of titrabil acid and fourth one is the excretion of ammonium ions. Now coming to the in short discussion of acid-based disorders.
There are three main parameters in the acid-base disorders the first is the pH. The normal range of pH is 7.35 to 7.45. If it is below 7.35 it is acidosis. If it is above 7.45 it is alkalosis.
Now second best parameter in the blood gas analysis is bicarbonate level. The normal concentration of bicarbonate is 22 to 26 millimole per liter. If there is decrease in the bicarbonate, it is metabolic acidosis. If there is increase in the bicarbonate level it is metabolic alkalosis. Then third parameter is partial pressure of CO2 which measures the dissolved carbonic acid concentration.
The normal range is 35 to 45 mmHg. If acid increases, it is acidosis. If partial pressure of CO2 or carbonic acid increases, that indicates respiratory acidosis. If carbonic acid decreases, it indicates respiratory acidosis. So these are the three parameters pH, bicarbonate and partial pressure of CO2.
Now look the parameter which corresponds with the pH is the primary defect. means if there is decrease in the bicarbonate level means acidosis and decrease in the pH means acidosis. If pH is decreased and bicarbonate level decrease, it means it is a case of metabolic acidosis.
acidosis. Those who correspond with the pH is the primary defect. Similarly, if there is increase in the partial pressure of CO2 and decrease in the pH, that means it is a primary defect respiratory acidosis.
Those who correspond with the pH is the primary defect and remaining one is the compensatory mechanism. So if there is increase in the the pH more than than 7.45 it is alkalosis. If it is corresponds with the increase in the bicarbonate that means it is metabolic alkalosis or if it is corresponds with the decrease in the partial pressure of CO2 it means it is respiratory alkalosis and remaining is the metabolic compensation. In the next video lecture we will discuss about the different disorders of acid-base balance in that we will discuss thoroughly with the metabolic acidosis, alkalosis, respiratory acidosis This is all about the general concept of acid-base regulation.
Thank you. Keep watching.