Topic 37 - The transport of oxygen, and carbon dioxide Flashcards

1
Q

Words to include

A
  • 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
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2
Q

Topics to include in the essay

A
  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
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3
Q

What is the respiratory gas exchange determined by?

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

Oxygen transport

General

A
  • 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
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5
Q

Oxygen transport

Factors affecting the Hb-O2 affinity

A
  • Normally:
    • 37˚C body temperature
    • 40 mmHg partial pressure of CO2
    • Average 2,3-DPG concentration
    • pH 7.4
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6
Q

Oxygen transport

Oxygen saturation curve

A
  • 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

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7
Q

CO2 transport

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

A
  • Dissolved in plasa (10%)
  • Converted to HCO3- (70%)
  • Carmamin Hb (20%)
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8
Q

CO2 transport

Hamburger shift

A
  • 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
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9
Q

CO2 transport

CO2 dissociation curve

A
  • 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

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