chemical buffers 2
- A chemical buffer is a mixture of two chemicals that interact in such a way to resist pH changes when either an acid or a base is added to the system.
- In the human body, since pH needs to be maintained in a very narrow range, it would be correct to assume that the body contains buffer systems.
4 different buffers systems in the body
- the [H2CO4]:[HCO3] buffer system
- the protein buffer system
- the haemoglobin buffer system
- the phosphate buffer system
the H2CO3 : HCO3- Buffer Pair 4
- An example of a chemical buffer system is the carbonic acid/bicarbonate buffer pair which dissociates following this chemical equation: H2CO3 ↔ HCO3- + H+
- When a base is added to a solution with this buffer, the base will bind the free H+, which results in the reaction moving forward so more H+ dissociates.
- The opposite is true when an acid is added to the solution.
- The reaction will move in the backwards direction so less H+ dissociates.
what occurs when a strong acid is added to an unbuffered solution
When HCl is added to an unbuffered solution, all the added H+ remain free and contribute to the acidity of the solution.
what occurs when a strong acid is added to a buffered solution
When HCl is added to the buffered solution, bicarbonate ions, HCO3-, bind with some of the added H+, and remove them from solution so they do not contribute to the acidity of the solution
significance of the H2CO3:HCO3- buffer pair 2
- The H2CO3:HCO3- buffer pair is the most important buffer in the human body, as it is responsible for buffering pH changes arising from everything other than CO2-generated H2CO3.
- It cannot buffer against changes in H2CO3 or HCO 3- because a buffer system cannot buffer itself
the H2CO3:HCO3- buffer pair is highly effective for 2 reasons
- Both H2CO3 and HCO3- are present in high quantities in the extracellular fluid (ECF), meaning this system has a high capacity for buffering changes in pH.
- Both H2CO3 and HCO 3- are highly regulated in the body to keep their concentrations relatively stable. The kidneys regulate HCO3- while the respiratory system regulates H2CO3 by regulating CO2
describe how the H2CO3:HCO3- buffer pair operates to minimize changes in pH in intense exercise (3)
- As you know, intense exercise results in the formation of lactic acid.
- This lactic acid means a higher concentration of H+ in the body, which will bind to HCO3- and drive the reaction to the left.
- This effectively removes the H+ so that it cannot increase the acidity of the ECF.
describe how the H2CO3:HCO3- buffer pair operates to minimize changes in pH in vomiting
The opposite also happens when there is a decrease of H+, which occurs following vomiting, in which the H2CO3 dissociates to release a H+ and prevent the ECF from becoming too basic
henderson-hasselbach equation 4
- This equation defines the relationship between H+ and a buffer system pair.
- This equation allows you to calculate the pH around which the buffer pair works.
- pH= pKa + log[HCO 3- / H2CO3]
- In the body, the concentration of H2CO3 is essentially the concentration of CO2, so we rewrite the equation as:
pH= pKa + log[HCO 3-/ CO2]
Note: pKa is constant for a given acid
the protein buffer system 4
- Proteins are excellent buffers because they are composed of amino acids.
- Amino acids contain many acidic and basic groups that can give up or accept H+, respectively.
- This buffer system is very important for intracellular fluids as the insides of cells are very rich in protein.
- There are proteins in the plasma, but they do not play a significant role there when compared to the H2CO3 : HCO3- system.
protein buffer system: what happens if the pH of the intracellular fluid rises or falls 2
- If pH rises In alkaline medium, amino acids acts as acids and release H+
- If pH falls In acidic medium, amino acids acts as bases and absorb H+
the haemoglobin buffer system 3
- Recall from Module 03 that haemoglobin (Hb) is a protein found within red blood cells that plays an important role in gas transport.
- It is also an essential buffer of H+ generated from metabolically produced CO2.
- Without it, the venous blood would become too acidic.
how the haemoglobin buffer system operates to ensure venous blood doesn’t become too acidic 3
- CO2 in Plasma:
As CO2 leaves the tissues and enters the blood, most of it forms H2CO3 in the red blood cells with help from the enzyme carbonic anhydrase. - O2 in Plasma:
Most of this H+ will immediately bind to haemoglobin and no longer add to the acidity of the body fluids. This frees up the oxygen bound to haemoglobin so that it is released to the tissues. - HCO3- in Plasma:
Some of the H2CO3 will immediately dissociate into HCO3- and H+
the phosphate buffer system 7
- This buffer system uses an acid phosphate salt that can donate a H+ when [H+] falls or accept an H+ when [H+] increases as defined by this equation:
Na2HPO4 + H+ <-> Na H2PO4 + Na+ - Although this is a very good buffer system, the concentration of the acid phosphate salt is very low in ECF so it does not play a major role.
- Inside cells, however, this buffer system does play an important role because the concentrations of phosphates are higher
- The most important role for the phosphate buffer system is actually to buffer the pH of the urine.
- Our diet is generally rich in phosphates and the excess phosphate is filtered by the kidneys but not reabsorbed.
- It builds up in the tubular fluid where it buffers any excreted H+.
- It is the only buffer system present in the urine
chemical buffer systems are the first line of defense 5
- These chemical reactions occur in just fractions of a second to either add or remove H+ from the body fluids.
- Because of their speed, chemical buffers are considered the first line of defense against changes in H+.
- Even though chemical buffers are very quick at removing H+ from body fluids, there is a limited capacity for them to absorb H+.
- In other words, the buffer systems cannot face the constant addition of H+ to the body fluids without eventually becoming overwhelmed.
- The chemical buffer systems are only able to remain effective due to the eventual removal of H+ by the respiratory and renal systems. which eliminate H+ from the body (dont buffer it)
