Module 5 Section 2

Question 1

chemical buffers

Answer 1

• 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

Question 2

4 buffer systems of the body

Answer 2

1. the [H2CO4]:[HCO3] buffer system
2. the protein buffer system
3. the haemoglobin buffer system
4. the phosphate buffer system
   each of them serve a specific purpose

Question 3

the H2CO3:HCO3- buffer pair

Answer 3

• carbonci acid/bicarbonate buffer pair which dissociates following the chemical equation shown
• 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 backwards so less H+ dissociates

Question 4

unbuffered solution

Answer 4

when HCl is added to an unbuffered solution, all the added H+ remain free and contribute to the aciditiy of the solution

Question 5

buffered solution

Answer 5

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

Question 6

significance of the H2CO3:HCO3- buffer pair

Answer 6

• the most important buffer in the human body, as it is responsible for buffering pH changes arising from everythig other than CO2-generated H2CO3
• it cannot buffer against changes in H2CO3 or HCO3- because a buffer system cannot buffer itself

Question 7

2 reasons H2CO3:HCO3- buffer system is so effective

Answer 7

1. both H2CO3 and HCO3- are present in high quantities int he ECF, meaning this system has a high capacity for buffering changes in pH
2. both H2CO3 and HCO3- 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

Question 8

how does the H2CO3:HCO3- buffer paur operate to minimize changes in pH during exercise and vomiting

Answer 8

exercise
- exercise results in the formation of lactic acid meaning a higher conc of H+ in the body
- this will bind to HCO3- and drive the reaction to the left
- this effectively removes the H+ so that it cannot increase the aciditiy of the ECF

vomiting
- there is a decrease of H+, whihc occurs following vomiting
- the H2CO3 dissociates to release H+ and prevent the ECF from becoming too basic

Question 9

henderson-hasselbalch equation

Answer 9

• 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

Question 10

protein buffer system

Answer 10

• proteins are excellent buffers because they are composed of aa
• aa contain many acidic and basic groups that can give up or accept H+
• 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

Question 11

haemoglobin buffer system

Answer 11

• 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

Question 12

CO2 in plasma

Answer 12

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

Question 13

HCO3- in plasma

Answer 13

some of the H2CO3 will immediately dissociate into HCO3- and H+

Question 14

O2 in plasma

Answer 14

• 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

Question 15

phosphate buffer system

Answer 15

• uses an acid phosphate salt that can donate a H+ when [H+] falls or accept an H+ when [H+] increases
• although this is a very good buffer system, the conc of the acid phosphate salt is very low in ECF so it does not play a major role
• inside cells, this buffer system does play an important role because the concentrations of phosphates are higher

Question 16

most important role of phosphate buffer system

Answer 16

• 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

Question 17

chemical buffer systems are the first line of defense

Answer 17

• these chemical reactions occur in just fractions of a second to either add or remove H+ form the body fluids
• because of their speed, chemical buffers are considered the first line of defense against changes in H+
• even though they are very quick at removing H+ from body fluids, there is a limited capacity for them to absorb H+
• the buffer systems cannot face the constant addition of H+ to the body fluids without eventually becoming overhwelemed
• the chemical buffer systems are only able to remain effective due to the eventual removal of H+ by the respiratory and renal systems
• the respiratory and renal systems contribute to pH control by the elimination of H+ from the body, not from buffering it