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
- 1 Hb binds 4 O2
- 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
- P50 / half-saturation
- 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
- HCO3- (majority)
- Hamburg shift
- RBC membrane imermable for K+
- Electrochemical gradient
- HCO3- leaves
- Cl- transported by capnophrine transporter
- RBC membrane imermable for K+
- Hydrogen acceptor
- Buffer base of blood
- Deprotonated hemoglobin
- HCO3- in plasma
- Buffer base of blood
- 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
- Anion exchange with HCO3-
- IC Cl- concentration ↑
- Haldane effect
- High O2 tension in lungs stimulates release of CO2 towards alveoli
2
Q
Topics to include in the essay
A
- What the respiratory gas exchange is determined by
- gas transport
- Oxygen transport
- Factors affecting the the hemoglobin-O2 affinity
- The oxygen saturation curve
- Myoglobin
- CO affinity to the curve
- CO2 transport
- Transport
- Hamburg shift
- CO2 dissociation curve
- Haldane effect
3
Q
What is the respiratory gas exchange determined by?
A
- Partial pressure
- Diffusion conditions
- Surface size (for the exchange)
- Metabolic activity ( O2 consumption /CO2 production)
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
-
1 Hb binds to 4 O2
- 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
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
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:
- Generation of carbamino compounds
- HCO3- and H+ decreases the pH
- Affects the curve i 2 ways:
-
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
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%)
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
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