Topic 37 - The transport of oxygen, and carbon dioxide

Question 1

Words to include

Answer 1

• Respiratory gas exchange
  
  • Partial pressure
  • Diffusion conditions
  • Surface size
  • Metabolic activity
    
    • O₂ consumption
    • CO₂ production
• Gas transport
  
  • Inhaled air
  • Exhaled air
  • Blood entering alveolar capillaries
  • Blood leaving alveolar capillaries
  • Blood leaving tissue capillaries
  • Blood entering tissue capillaries
  • Alveolar space
  • Tissue cells

The transport of oxygen

• Hemoglobin
  
  • 1 Hb binds 4 O₂
    
    • _​Saturation
    • Reversible binding
• Lungs → cells

Factors affecting the hemoglobin-O₂ affinity

• 37˚C body temperature
• 40 mmHg partial prssue of CO₂
• Average 2,3-DPG concentration
• pH 7.4
• Oxygen saturation curve
  
  • Sigmoidal
  • Half-saturation
    
    • 30 mmHg O₂
• pCO₂
  
  • P50 / half-saturation
    
    • Shift of curve
    • 30 mmHg
  • Shift to right
    
    • Hb O₂ affinity ↓
    • Tissues
  • Shift to left
    
    • Hb O₂ affinity ↑
    • Lungs
• pH
  
  • Higher H⁺ concentration = lower affinity for O₂
  • Bhor effect
  • Lactic acid
• Partial pressure of CO₂
  
  • Carbamino compounds
  • HCO₃^- & H⁺ decreases pH
• Temperatre
  
  • ↑ temperature denaturates the bond between O₂ and Hb
• 2,3-DPG - organic phosphate
  
  • Binding of 2,3-DPG to Hb → tense state → decreases affinity for O₂
• pH
  
  • ↓: right shift
  • ↑: left shift
• CO₂, temperature, 2,3-DPG
  
  • ↓: left shift
  • ↑: right shift

Myoglobin

• High affinity of oxygen
• Saturated at lower oxygen levels
• Hb: oxygen transport
• Myoglobin: oxygen storage

CO affinity to the curve

• High affinity of Hb (higher than O₂)
• Carboxyhemoglobin
• Deadly

CO₂ transport

• Intravasal space
  
  • Capillary
• High diffusability
  
  • Red blood cells
• Transport:
  
  • HCO₃^- (majority)
    
    • With help of carbonic anhydrase
    • Enters plasma
  • Physically dissolved in plasma
  • Protein bound in plasma
    
    • Carbamino-hemoglobin
• Hamburg shift
  
  • RBC membrane imermable for K⁺
    
    • Electrochemical gradient
    • HCO₃^- leaves
    • Cl^- transported by capnophrine transporter
• Hydrogen acceptor
  
  • Buffer base of blood
    
    • Deprotonated hemoglobin
    • HCO₃^- in plasma
• Carbamino compounds (20% of CO₂ transport)
  
  • CO₂ + NH₂ part of protein
  • Deoxyhemoglobin (binds easy)
• HCO₃^- (70% of CO₂ transport)
  
  • Carbonic anhydrase converts

CO₂ dissociation curve

• Quantity of CO₂ transported in bloods as a function of partial pressure of CO₂
• Venous blood
  
  • pO₂: 40 mmHg
  • pCO₂: 46 mmHg
• Arterial blood
  
  • pO₂: 95 mmHg
  • pCO₂: 40 mmHg
• Haldane effect
  
  • High oxygen tension of lungs stimulates relase of CO₂

Summary figure - CO₂ transport

• CO₂
  
  • 10% to plasma
  • 70% to HCO₃^-
  • 20% to carbamino Hb
• Deoxyhemoglobin + H⁺
• Hamburg shift + H₂O migration
  
  • IC Cl^- concentration ↑
    
    • Anion exchange with HCO₃^-
      
      • Through capnophorine transporter
• Haldane effect
  
  • High O₂ tension in lungs stimulates release of CO₂ towards alveoli

Question 2

Topics to include in the essay

Answer 2

1. What the respiratory gas exchange is determined by
2. gas transport
3. Oxygen transport
   
   1. Factors affecting the the hemoglobin-O₂ affinity
   2. The oxygen saturation curve
   3. Myoglobin
   4. CO affinity to the curve
4. CO₂ transport
   
   1. Transport
   2. Hamburg shift
   3. CO₂ dissociation curve
      
      1. Haldane effect

Question 3

What is the respiratory gas exchange determined by?

Answer 3

1. Partial pressure
2. Diffusion conditions
3. Surface size (for the exchange)
4. Metabolic activity ( O₂ consumption /CO₂ production)

Question 4

Oxygen transport

General

Answer 4

• Oxygen are bound chemically and physically in blood
  
  • Bunsen’s coefficient (significantly more O₂ and CO₂ found in the blood than expected)
• Main actor: hemoglobin (Hb)
  
  • 1 Hb binds to 4 O₂
    
    • Saturation ​is fast
    • Binds reversible
• Under nromal conditions average oxygen consumption is 300 ml oxygen/minute/100 kg bodyweight
  
  • This oxygen must be forwarded from the lung to the cells

Question 5

Oxygen transport

Factors affecting the Hb-O₂ affinity

Answer 5

• Normally:
  
  • 37˚C body temperature
  • 40 mmHg partial pressure of CO₂
  • Average 2,3-DPG concentration
  • pH 7.4

Question 6

Oxygen transport

Oxygen saturation curve

Answer 6

• The oxygen saturation curve is sigmoidal
  
  • ​Half saturation occurs at 30 mmHg
• ​pCO₂
  
  • ​Half saturation reflects the shift of the curve - 30 mmHg
  • Shift to right
    
    • Hb-O₂ affinity ↓
    • Occurs in tissues
  • Shift to left
    
    • Hb-O₂ affinity ↑
    • Occurs in lungs
• pH
  
  • ​Higher H⁺ concentration = lower affinity for O₂
  • Bohr effect
    
    • ​O₂ affinity and change in pH or CO₂
    • Carbonic acid
  • Metabolic byproducts: lactic acid
• Partial pressure of CO₂
  
  • Affects the curve i 2 ways:
    
    1. Generation of carbamino compounds
    2. HCO₃^- and H⁺ decreases the pH
• Temperature
  
  • ​Increased temperature denaturates the bond between oxygen and Hb
• 2,3 DPG
  
  • Binding of 2,3 DPG to Hb causes it to go into a tense state​ = affinity for oxygen ↓
• CO
  
  • ​COhave a higher affinity toHbthanO₂
  • CO + Hb → CarboxyHb
  • CO binding of Hb is irreversible
  • Deadly
• Myoglobin
  
  • ​Found in skeletal muscle tissue
  • 1 hem group binds to 1 O₂
  • Higher affinity for oxygen than Hb, and becomes saturated at lower oxygen levels
  • Hemoglobin: transport oxygen
  • Myoglobin: store oxygen
• pH
  
  • ↓: right shift
  • ↑: left shift
• CO2, temperature, 2,3-DPG
  
  • ↓: left shift
  • ↑: right shift

​

Question 7

CO₂ transport

What happens with the CO₂ when it gets into the red blood cells?

Answer 7

• Dissolved in plasa (10%)
• Converted to HCO₃^- (70%)
• Carmamin Hb (20%)

Question 8

CO₂ transport

Hamburger shift

Answer 8

• The RBC memebrane is impermable for K⁺, so it can not leave the cell to establish electroneutrality
• Instead of this, the increased HCO₃^- concentrantion stimulates the activity of the plasma membrane anion exchanger
• This transporter (capnophorine sensitive) exchanges HCO₃^- to Cl^-
• This process ensures electroneurality
• IC Cl^- concentration increases significantly
• The Hamburger shift occurs

Question 9

CO₂ transport

CO₂ dissociation curve

Answer 9

• Linear in shape (compared to O₂ dissociation curve)
• When increasing ventilation, the CO₂ excretion is increased in lung regions of high and low V/Q ratios. In contrast, increasing ventilation preferentially increases O₂ content of blood in low V/Q ratio areas of lung
• The CO₂ content of the venous and arerial blood can be calculated based on the Henry-Dalton Law
  
  • ​Venous blood: 24.4 mmol/l
  • Arterial blood: 22.1 mmol/l
• Haldane-effect:
  
  • ​Deoxygenation of the blood increases its ability to carry CO₂, and vice versa
  • High O₂ tension in the lung increaingly stimulates the release of CO₂

Figure: CO₂ dissociation curve