Gas Diffusion Flashcards
Gas exchange in respiration steps
1.Deoxygenated blood from pulmonary artery reaches alveoli (low O2 and high CO2)
2. CO2 diffuses into alveoli and O2 diffuses into capillary
3. Gas in systemic/tissue capillary travels to tissue where O2 diffuses into the cell and CO2 diffuses into capillary
Gas pressure changes during exercise
-during exercise, tissue O2 pressure levels drop and CO2 pressure levels increase
-the increase in the pressure difference (P1-P2) will result in enhanced gas exchange
Pulmonary gas flow in conducting zone
Different gas moves together through the conducting airway
- bulk flow, high velocity, turbulent or laminar
Pulmonary gas flow in alveoli
Once gases reach the alveoli, there is a decrease in diameter and an increase in surface area. This results in flow decreasing its velocity
-At a slow velocity, gas movement occurs individually through diffusion based on properties of each gas
-Gases diffuse from high partial pressure to low partial pressure
Goals of pulmonary gas diffusion
1.to diffuse O2 from alveoli into blood
2. to diffuse CO2 from blood to alveoli
Pulmonary gas diffusion layers
-must diffuse through tissues and liquid phase
Layers:
1.pulmonary fluid and surfactant
2.alveolar epithelium and basement membrane
3.interstitial space (fluid can build up here making gas movement more difficult)
4.capillary basement membrane and endothelium
5.plasma
6.RBC
What laws impact rate of diffusion of gases?
-Henry’s Law
-Fick’s Law
Henry’s Law equation
Concentration dissolved gas in liquid (C)= gas constant (K) X partial pressure of gas (P)
Henry’s Law
-the amount of dissolved gas in a solution is proportional to its partial pressure above the liquid
Bidirectional
Henry’s law in alveoli
-O2 must move from gas to liquid phase, and CO2 moves from liquid to gas phase
*if you double the partial pressure, then you double the concentration of O2 dissolved in liquid
Why is 100% oxygen used for animals in respiratory distress?
-because of Henry’s Law
-higher partial pressure results in an increase in dissolved oxygen in the blood
Fick’s Law Equation
Rate of gas exchange= surface area (A) x diffusion coefficient (D) X ((Pressure difference Phigh-Plow)/Barrier thickness (T))
Fick’s Law
-the rate of gas diffusion across a permeable barrier is dependent on surface area, diffusion coefficient, pressure difference, and barrier thickness
What happens to rate of gas diffusion when surface area increased?
-An increase in diffusion
*Reason why compliant lung is good and atelectasis is bad**
What happens when pressure difference has increased?
Increase in diffusion
Reason why 100% O2 is good
What happens when barrier thickness is increased?
-diffusion is decreased
Reason why inflammation/edema is bad
Diffusion coefficient of CO2 compared with O2
CO2 is 20x more soluble than O2
Pressure gradients for O2 compared with CO2
-O2: higher pressure inside alveoli, lower pressure outside
-CO2: higher pressure outside alveoli, lower pressure inside
**CO2 has smaller gradient than O2 gradient
Diffusion rate of CO2 compared with O2
CO2 has a slightly higher diffusion rate than O2 overall
-Even though CO2 has a smaller pressure difference
CO2 being higher allows for effective diffusion but is also regulated over a narrower range (because tighter control needed due to its effect on blood pH)
Factors that impair diffusion
-increased barrier thickness
-decreased surface area
-decreased O2 pressure in the alveoli
What occurs when O2 coming in is affected?
-hypoxemia
What occurs when CO2 going out is affected?
-hypercapnia
What can cause increased barrier thickness?
-fibrosis
-inflammation/pneumonia
-edema (interstitial space)
What can cause decreased surface area?
-fibrosis
-low surfactant (high surface tension)
-bronchus obstruction (mucous)
What can cause decreased O2 pressure inside the alveoli?
-altitude/elevation
-pollution
-re-breathing (anesthesia)
Effect of altitude
-decrease O2 partial pressure with altitude
-low alveolar O2 pressure results in decreased pressure difference and therefore a reduced diffusion rate
What determines O2 alveolar pressure?
1.rate of O2 entry into lung (increase O2 alveolar pressure)
2.Rate of O2 absorption into blood (decrease CO2 alveolar pressure)
Max alveolar O2 pressure
-it cannot exceed 150 mm Hg (in moist tracheal air)
Alveolar O2 pressure and Gas ventilation at rest
-Avg alveolar O2 pressure= 104 mm Hg
-achieved with gas ventilation rate of 5 L/min and O2 consumption of 250 ml O2/min
Alveolar O2 pressure and gas ventilation during exercise
-during exercise, there is an increase in O2 demand and therefore an increase in rate of O2 absorption into blood which decreases alveolar O2 pressure
-ventilation rate must increase 4-fold to 20L/min to achieve O2 consumption of 1000ml O2/min
What determines CO2 alveolar pressure?
1.rate of CO2 entering the lung (increase CO2 alveolar pressure)
2.rate of CO2 leaving the lung (decrease CO2 alveolar pressure)
Average alveolar CO2 pressure
40 mm Hg
Alveolar CO2 pressure and gas ventilation at rest
-Avg alveolar CO2 pressure= 40 mm Hg
-CO2 excretion rate at 200ml CO2/min
Alveolar CO2 pressure and gas ventilation during exercise
-during exercise, an increase in CO2 production occurs (Kreb’s cycle) resulting in an increased rate of CO2 entering the lung/alveolar CO2 pressure
-ventilation rate increases 4x to reach CO2 excretion rate at 800 ml/min in order to maintain average 40mm Hg
Proportionality of alveolar pressure for CO2 and O2
-Alveolar pressure of O2 is proportional to ventilation
-Alveolar pressure of CO2 is inversely proportional to ventilation
