L11 Transport And Exchange Of Gases Flashcards
What is the main factor influencing the diffusion of gases between air, blood, and tissues?
Partial pressures
The direction of diffusion depends on the difference in partial pressures (P1 - P2) rather than concentration differences.
What is the relationship between partial pressures and diffusion direction?
Gases diffuse from regions of high partial pressure to regions of low partial pressure
Equilibrium occurs when partial pressures are equal, stopping diffusion.
What determines the total pressure of a gas mixture?
Total pressure = sum of all individual partial pressures
Partial pressure is denoted by an italic P; subscripts indicate measurement locations.
What is the partial pressure of O2 in atmospheric air at 101.3 kPa?
21.2 kPa
This is calculated as 101.3 kPa x 0.21.
What happens during diffusion in the lungs regarding O2 and CO2?
O2 diffuses into the alveolar fluid; CO2 diffuses from alveolar fluid into the air
Both diffusions occur simultaneously but independently.
What factors limit diffusion of gases?
- Thickness of the diffusion barrier (T)
- Surface area (A)
- Solubility of the gas
- Molecular weight (MW)
The rate of diffusion is influenced by these factors.
What is the rate of diffusion equation?
Rate of diffusion = (P1 - P2) x A x solubility x (1 / √Mol. Wt.)
This equation considers the partial pressure difference, area, solubility, and molecular weight.
What is the respiratory quotient (RQ) related to CO2 produced and O2 consumed?
0.8
This ratio indicates the relationship between the volume of CO2 produced and O2 consumed.
What percentage of O2 is carried by hemoglobin?
98.5%
Only 1.5% of O2 is dissolved in plasma.
What is the role of hemoglobin in O2 transport?
Enhances blood’s capacity to carry O2 by 67 times
Hemoglobin binds O2 through its ferrous Fe2+ at the center of each heme group.
What is the O2-Hb dissociation curve’s shape and why?
Sigmoidal shape due to ‘co-operative’ binding
Binding of one O2 increases the affinity of the remaining binding sites for O2.
What factors influence the binding of O2 to hemoglobin?
- Partial pressure of O2 (PO2)
- Partial pressure of CO2 (PCO2)
- pH
- Temperature
- 2,3 diphosphoglycerate (2,3 DPG)
These factors can shift the O2-Hb dissociation curve.
What occurs in the alveoli that affects pH and temperature?
Loss of CO2 raises pH; evaporation lowers temperature
These changes lead to a leftward shift in the O2-Hb dissociation curve.
What happens in tissues that affects O2 unloading from hemoglobin?
CO2 production lowers pH; metabolism raises temperature
These changes cause a rightward shift, aiding O2 unloading.
What is the significance of 2,3 DPG in O2 transport?
Accumulation during high O2 consumption
It influences hemoglobin’s affinity for O2.
What is the typical O2 content in arterial blood at rest?
20 ml O2/dl blood, 97% saturation
This reflects the O2-Hb binding capacity.
What is the typical O2 content in mixed venous blood at rest?
15 ml O2/dl blood, 75% saturation
This indicates the amount of O2 extracted by tissues.
What happens to O2 levels in the blood returning to the heart via the pulmonary vein?
P O2 drops from 13.3 to 12.5 kPa
This is due to mixing with deoxygenated blood from bronchial arteries.
What is the effect of anemia on O2 transport?
Reduced O2 carrying capacity due to decreased hemoglobin content
Alveolar PO2 may be normal, but tissue PO2 can be low.
What is the significance of P1 - P2 in gas diffusion?
It is the driving force for both diffusion and uptake by hemoglobin
PO2 is the main determinant of O2 content and saturation.
What is the main determinant of O2 content and % saturation of Hb with O2?
P O2
List the four important measures of O2 transport.
- Reduced O2 carrying capacity
- Reduced red blood cell count
- Alveolar P O2 normal, % sat. normal
- Mild tissue hypoxia (low tissue P O2)
What happens if there is not enough Hb?
Reduced O2 content and saturation
What is the Hb content in normal conditions?
100%
