Topic 2 The Respiratory System: Bohr Effect

Question 1

• Refers to the shift in oxygen dissociation curve caused by changes in concentration of CO2 or pH
• Hemoglobin O2 binding affinity decreases under conditions of low pH (results from high CO2 and H+)
• Decreased binding affinity leads to oxygen being released by hemoglobin
• The corollary is true – a decrease in CO2 or increase in pH results in hemoglobin binding more O2
• Oxygen diffuses from alveolar air into the blood, while CO2 diffuses from blood into lungs

Answer 1

Bohr Effect

Question 2

• High concentration of CO2, it diffuses into blood and red blood cells where carbonic anhydrase converts it into H2CO3
• H2CO3 becomes HCO3- and H+
• This build up of H+ explains why high CO2 = low pH
• Hemoglobin comes into play as it interacts with H+ to form a reduced form of hemoglobin that has a lower affinity for O2 and greater for CO2 causing O2 to be released

Answer 2

1. High CO2

Question 3

• High CO2 and low pH are related
• Low pH means greater presence of H+ ions
• Hemoglobin structure is altered to the reduced form that will release its oxygen

Answer 3

2. Low pH

Question 4

• At higher blood temps, hemoglobin becomes less likely to bind to oxygen and releases oxygen to tissues

Answer 4

3. High Temperature

Question 5

• Aka 2,3-BRG
• Produced from intermediate compound in glycolysis and decreases the affinity of hemoglobin for oxygen
• At low O2 levels, an enzyme catalyzes the synthesis of 2,3-DPG, hence, high 2,3-DPG = low affinity of hemoglobin for O2
• Helpful for unloading oxygen during anemia or at high altitudes
• At high O2 levels, oxyhemoglobin inhibits the enzyme that synthesizes 2,3-DPG leading to low concentrations of the compound
• Use the mnemonic “CADET, face right!” to remember the factors (CO2, Acid, 2,3-DPG, Exercise, and Temperature) that shift the oxygen dissociation curve to the right. A right shift involves physiological states where tissues need more oxygen. For example, during exercise, muscles have a higher metabolic rate, and we need more oxygen. So, the CO2 and lactic acid, and the temperature rises. As a result, oxygen is released easily

Answer 5

4. High 2,3-DPG

Question 6

• When tissues are high in CO2 and H+ the tissues are not getting a lot of O2 and we want to oxygenate them
• Then when hemoglobin is near the tissues is exposed to the higher CO2 and H+ levels and changes its structure to the reduced form
• Reduced form releases O2 to the deoxygenated tissues and binds to CO2

Answer 6

Bohr Effect

Question 7

• CO2 wants out and is released
• H+ concentration is lower due to bicarbonate being converted back into CO2 for release
• Hemoglobin changes back to non-reduced state that binds to oxygen
• Bohr effect relates to how CO2 and H+ affect hemoglobin’s affinity for O2

Answer 7

Bohr Effect at Lungs

Question 8

• The left shift on the oxygen dissociation curve results in oxygen being held more tightly by hemoglobin
• This occurs when the factors from the right shift are reversed in their direction meaning:
  1. Low CO2
  2. High pH
  3. Low temp
  4. Low 2,3-DPG

Answer 8

Bohr Effect