pH and Buffers

Question 1

What difference is in Ka for strong bases and acids?

Answer 1

if Ka is less than one then the acid is “weak”

is the Ka is greater that 10, it is “strong”

Question 2

Examples of physiological bases.

Answer 2

HCO3- , HPO4 2- , H2PO4- and
proteins-

Question 3

Characteristic of a physiological base.

Answer 3

comparatively strong bases because they have a relatively strong affinity for H+ ions forming weak acids (relatively slight dissociation)

Question 4

Ampholytes?

Answer 4

Substances which can function both as acids and bases are called ampholytes.

Question 5

pH formula?

Answer 5

pH = -log [H+]

Question 6

What is the normal plasma pH?

Answer 6

7.35 - 7.45

Question 7

What effect do pH imbalances have on the nervous system?

Answer 7

H+ imbalances cause K+ imbalances because transporter proteins in kidneys move H+ and K+ in an antiport fashion

In acidosis: neurons become less excitable and CNS depression can result

In alkalosis: hyperexcitable

Question 8

Definition of a buffer?

Answer 8

Solutions that resist change in pH upon the addition of small volumes of acid or base
Buffers are the mixtures of weak acids and their salts of strong bases (and vice versa)

Question 9

What does the Henderson-Hasselbalch equation describe?

Answer 9

The quantitative relationship between
– pH,
– the buffering action of a weak acid and its conjugate base and
– the pKa value of weak acid is given by the

Question 10

What are the applications of the Henderson- Haselbalch equation?

Answer 10

1. Calculation of concentrations of constituents of buffers
2. Determination of the proportions of conjugate pairs that exist at a given pH
3. Determination of pH of buffers
4. Calculation of the effective concentration of the permeable form of the drug at its site of absorption
5. Predicting about renal clearance of a drug

Question 11

Calculation of the pI for more complex amino acids?

Answer 11

the pI is the average of the pKa values that represent the boundaries of the zwitterionic form of the molecule.

If additional acidic or basic groups are present as side-chain functions, the pI is the average of the pKa s of the two most similar acids.

Question 12

Calculation of the pI for more complex amino acids?

Answer 12

the pI is the average of the pKa values that represent the boundaries of the zwitterionic form of the molecule.

If additional acidic or basic groups are present as side-chain functions, the pI is the average of the pKa s of the two most similar acids.

Question 13

What is a “Physiological buffer”?
Examples?

Answer 13

A system that controls the output of acids, bases or CO2
* urinary system buffers the greatest quantity, which takes several hours
* respiratory system buffers within minutes, limited quantity

Question 14

What are “Chemical Buffer systems”?

Answer 14

– restore normal pH in fractions of a second
– bicarbonate, phosphate and protein systems bind H+ and transport H+ to an exit (kidney/lung)

Question 15

What are the two types of Buffer systems?

Answer 15

1. Physiological buffer
2. Chemical Buffer system.

Question 16

What is a “Buffering Capacity”?

Answer 16

The efficiency of a buffer in maintaining a constant pH on the addition of small amounts of acid or base is called as its buffering capacity.

Question 17

What is Buffering Capacity determined by?

Answer 17

– the pH of the solution; Buffers work best within 1 pH unit of their pKa (± 1).
– the concentration of the buffer, the stronger the buffer, the greater its buffering capacity.
– Ratio of acid to conjugate base.

Question 18

What are the three most important buffers in the body?

Answer 18

1. Urine
2. Blood
3. ICF

Question 19

What does a urine buffer involve?

Answer 19

Phosphate and Ammonia Buffers

Question 20

What do the blood buffers involve?

Answer 20

Bicarbonate, Protein and
Haemoglobin (in RBC) buffers

Question 21

What are the pH buffers in the ICF?

Answer 21

Proteins and Phosphates

Question 22

What are the three types of physiological buffers in the body? and how fast do they act?

Answer 22

1) Chemical Buffers
* React very rapidly (less than a second) 2) Respiratory Regulation
* Reacts rapidly (seconds to minutes)
3) Renal Regulation
* Reacts slowly (minutes to hours)

Question 23

What are the 3 Major Buffer Systems in the blood?

Answer 23

1. Protein Buffer systems.
2. Carbonic acid-bicarbonate buffer system.
3. Phosphate buffer system.

Question 24

In which space of the body does the carbonic acid-bicarbonate buffer system act?

Answer 24

ECF

Question 25

Where does the phosphate buffer system act?

Answer 25

ICF and urine

Question 26

Explain protein buffer systems.

Answer 26

• Protein buffer systems are made up of amino acids, which have both acidic and basic groups.
• Amino acids can accept or release H+ ions to maintain pH balance in response to changes in the environment.
• Protein buffer systems are more concentrated than other buffer systems and are important for maintaining the pH balance of bodily fluids and tissues.

Question 27

What is the basis of the Histidine R group buffer system?

Answer 27

R group (side-chain) of histidine has an imidazole functional group that undergoes reversible protonation.

Question 28

How does the Histidine Buffer system work?

Answer 28

Because the pKa of the imidazole R group is 6.0, histidine residues in proteins help buffer the pH of the cell cytosol and extracellular fluids around neutrality.

Question 29

What are the 2 buffer systems for the cell cytosol?
What is Ka of these two buffer systems?

Answer 29

1. Histidine R group system - 6.0
2. Phosphate buffers - 6.86

Question 30

Describe the Haemoglobin Buffer System

Answer 30

• CO2 diffuses across RBC membrane: – no transport mechanism required
• As carbonic acid dissociates:
  – bicarbonate ions diffuse into plasma
  – in exchange for chloride ions (chloride shift)

Question 31

What is the significance of the Hemoglobbin buffer system?

Answer 31

• Hydrogen ions are buffered by haemoglobin molecules
• Is the only intracellular buffer system with an immediate effect on ECF pH
• Helps prevent major changes in pH when plasma PCO2 is rising or falling

Question 32

What does the “Bicarbonate Reserve” mean with respect to the Carbonic Acid- Bicarbonate Buffer system?

Answer 32

It has NaHCO3
NaHCO3 can break down to give HCO3-
OR
take up HCO3- using Na+

Question 33

Which two organs regulate the PCO2 and HCO3-?

Answer 33

lungs and kidneys

Question 34

Explain how the respiratory rate can change depending on the acid-base balance.

Answer 34

• Carbon dioxide in the blood is converted to bicarbonate ions and transported in the plasma
• Increases in hydrogen ion concentration produce more carbonic acid
• Excess hydrogen ions can be put out with the release of carbon dioxide from the lungs
• Respiratory rate can rise and fall depending on changing blood pH

Question 35

What is the phosphate buffer system?

Answer 35

H2PO4-  HPO42- + H+
reactions that proceed to the right release H+ and decrease the pH, and those to the left increase the pH

Question 36

Where are the phosphate buffers the most important?

Answer 36

Important in the ICF and renal tubules
– where phosphates are more concentrated and function closer to their optimum pH of 6.8.

Question 37

What is the importance of the phosphate buffer system?

Answer 37

constant production of metabolic acids creates pH values from 4.5 to 7.4 in the ICF, avg. 7.0

Question 38

What are the 4 methods of renal regulation?

Answer 38

1. Bicarbonate reabsorption
2. H+ secretion
3. Combination of H + in the tubular fluid with phosphate and ammonia
4. New bicarbonate generation

Question 39

Describe the NaHPO4 buffer system and ammonia buffer system

Answer 39

• H+ is taken up by Na2HPO4 and NaH2PO4 is formed and excreted
• NH3 takes up H+ and together with Cl-, forms NH4Cl which is excreted