Gas Exchange Flashcards
External Respiration
Pulmonary ventilation (Breathing) Pulmonary Gas Exchange
Components of Respiration
External Respiration
Internal Respiration
Transport of Gases through blood
Internal Respiration
Systemic tissue gas exchange
Cellular Respiration
Respiratory Cycle-Inspiration
During inspiration, the diaphragm contracts, increasing the volume of the thoracic cavity. This increase in volume results in a decrease in pressure, which causes air to rush into the lungs.
Respiratory Cycle-Expiration
During expiration, the diaphragm returns to an upward position, reducing the volume in the thoracic cavity. Air pressure thus increases, forcing air out of the lungs.
Partial Pressure of Gases
Partial Pressure of gases is the pressure exerted by a gas in a mixture of gases or liquids
Law of Partial Pressure
Dalton’s Law
The partial pressure of a gas in a mixture will equal the total pressure if that gas
Arterial Blood
PO2 and PCO2 equal alveolar PO2 and PCO2
Due to continuous ventilation PO2 and PCO2 should remain relatively constant
Factors that Determine Diffuse of O2 into blood
1) O2 pressure gradient between alveolar air and blood
2) Total functional surface are
3) Respiratory minute ventilation
4) Alveolar ventilation versus deadspace ventilation
Structural Factors that Facilitate Oxygen Diffusion from the Alveolar Air to the Blood
The walls of the alveoli and capillaries form only a very thin barrier for gases to cross. As little as half a micron.
The alveolar and capillary surfaces are large
The blood is distributed through the capillaries in a thin layer so that each red blood cell comes close to alveolar air.
Bohr Effect
Increased PCO2 at the tissue level will decrease the affinity between oxygen and Hb (dumping of O2 at the tissue level)
Haldane Effect
Increased CO2 loading caused by a decrease in PO2 (increase loading of CO2) at the tissue level
Rate of Diffusion
〖Diffusion 〗_gas= [(A x Cs)/T ] x ∆P According to Fick’s Law the membrane diffusion rate is affected by Surface Area (A) Solubility of Gas (Cs) Membrane Thickness (T) Partial Pressure (∆P)
Diffusion Rate and Surface Area
As surface area increases there will be a greater diffusion rate
Diffusion Rate and solubility coefficient
As solubility coefficient increased there will be an increase in diffusion rate
Diffusion Rate and Partial Pressure Gradient
As the partial pressure gradient increases there is an increase in diffusion rate
CO2 Diffusion versus O2
CO2 will diffuse 20 times faster than O2 due to the fact that it has a higher solubility (heavier molecule)
Graham’s Law
Gas diffusion rate is inversely proportional to the square root of the gram molecular weight (density)
the lighter the gas the faster the diffusion rate
Henry’s Law
Gas diffusion is directly proportional to the partial pressure
Basis of O2 therapy
Greater pressure=greater diffusion
Capillary Blood Transit
Capillary Transit Time=0.75 sec
Alveolar-Capillary Equilibrium-Within the first 0.25
Perfusion and Diffusion Limitations to O2 transfers
Decreased or increased blood flow
Thickened alveolar blood flow
CO Diffusion
Limited diffusion due to a strong affinity to Hgb
PP doesn’t rise easily
N2O Perfusion
Perfusion is limited
Equilibrium pressure is reached quickly, therefore more blood is needed to accept more N2O
Oxygen Diffusion Path Length
From alveolar gas to red blood cells
The path is less than 1/2 micron
