Lecture 18: Oxygen and Carbon dioxide exchange Flashcards
What is respiratory minute volume?
The amount of air breathed in a minute
How do you calculate respiratory minute volume?
Respiratory minute volume = tidal volume x Respiratory rate
What is tidal volume determined by?
Breathing strength
What is respiratory rate determined by?
Breathing speed
What is the unit for respiratory minute volume?
L/min
What is the unit for tidal volume?
L/breath
What is the unit for respiratory rate?
Breaths/min
What is dead space?
The air we breath in that doesn’t get to the alveoli so cannot go through gas exchange (air that can’t be used)
What is the approximate amount of dead space regardless of breath type?
150 mls
What is really important for breathing?
The amount of air that gets into the alveoli
What is Alveolar ventilation?
The amount of air that gets into the alveoli
How do you calculate alveolar ventilation?
(Tidal volume - Dead space) x Respiratory rate
Are tiny rapid breaths helpful?
No, because of dead space
What does gas diffusion depend on?
Partial pressures
What is daltons law?
In a gas mixture (air), each gas exerts its own individual pressure, called a partial pressure (P)
What does the pressure of a mixture of gases = ?
The sum total of the pressures of each individual gas
What is the goal of gas movement in respiration?
Move gas back and forth between the alveoli and the capillaries
Where do we want to transport inhaled air?
Into the capillaries
Where do we want to transport carbon dioxide?
Into the alveoli to be exhaled
What is Fick’s law of diffusion?
Gases move across the membranes between the alveoli and the capillaries by diffusion
What determines the rate of diffusion according to Fick’s law?
(3)
- Surface area of the membranes
- Thickness of the membranes
- Pressure difference between the two sides
What is Fick’s law equation?
F = (A/T) x d x (P1 - P2)
What does F stand for in Ficks law of diffusion equation?
Flux (amount flowing)
What does A stand for in Ficks law of diffusion equation?
Surface area
What does T stand for in Ficks law of diffusion equation?
Thickness
What does D stand for in Ficks law of diffusion equation?
Diffusion constant
What does P1 - P2 stand for in Ficks law of diffusion equation?
Pressure difference
What does the diffusion constant or coefficient for a substance depend on?
Gas solubility (S) and its molecular weight
On a per molecule rate how much faster does Carbon dioxide diffuse than Oxygen?
20x due to carbon dioxide’s higher solubility
What does the bulbous structure of alveoli and the high density of capillaries do?
Create lots of surface area for gas exchange
What is Emphysema?
A disease characterised by the dilation of the alveolar spaces and destruction of the alveolar walls
What does a reduction in surface area mean for oxygen exchange?
It is greatly reduced as there is less contact between the air and capillaries
What is the blood-air barrier mostly comprised of?
The alveolar and capillary walls
What’s is the distance between the alveolar air and the blood?
Small
What is a result of Pulmonary fibrosis?
Thickening and scarring of the alveolar membranes
What can cause Pulmonary fibrosis?
Chronic inflammation or exposure to industrial chemicals
What is the main factor for gas transfer?
Pressure difference
What does alveolar partial pressure of Oxygen depend on?
3
- Partial pressure of oxygen in inspired air
- Alveolar ventilation
- Oxygen consumption - Blood oxygen
What does alveolar partial pressure of carbon dioxide depend on?
(3)
- partial pressure of carbon dioxide in inspired air
- Alveolar ventilation
- Carbon dioxide production
Because Partial pressure of oxygen is usually constant, what is it the balance of that is most important in driving oxygen exchange?
Balance between oxygen consumption and alveolar ventilation
Alveolar partial pressure of carbon dioxide is usually determined by what because atmospheric partial pressure of carbon dioxide is negligible?
Balance between carbon dioxide production and alveolar ventilation
What do gasses diffuse down?
Their pressure gradients
