O2 and CO2 exchange Flashcards
What is the equation for respiratory minute volume (how much air we breathe in and out)?
Respiratory minute volume = Tidal volume (breathing strength) X Respiratory rate (breathing speed)
What is dead space?
The portion of every breath that gets stuck in the conducting portion of the respiratory system (doesn’t make it to the alveoli for gas exchange)
How much air can we get to the alveoli and why are rapid breaths not helpful?
Alveolar ventilation = (Tidal volume - dead space) X respiratory rate
Rapid breaths are not helpful because all you are doing is reducing tidal volume to basically nothing and then once you minus dead space that means that no air is getting to alveoli for gas exchange
What is Dalton’s law?
The pressure of a mixture of gasses is the sum total of the pressure of each individual gas.
So because in each different portion of air (inhaled air, alveolar air and exhaled air) there is a different proportion of each of the gasses, at each diff space the pressure is still the same overall because the different proportions of gasses add up to the same number in each different location
What determines the rate of diffusion?
- Surface area of the membranes (constant)
- Thickness of the membranes (constant)
- Pressure difference between the two sides (variable)
How does the surface area of membranes affect rate of diffusion
- Bulbous structure of alveoli and high density o capillaries creates lots of surface area for gas exchange.
- The larger the surface area, the more space there is for molecules to diffuse across it, so more molecules get across per unit time
What is emphysema
A disease characterised by dilation of the alveolar spaces and destruction of the alveolar walls
Reduction in surface area means less contact between the air and capillaries, so oxygen exchange is greatly reduced
How does the thickness of the membrane affect the rate of diffusion?
The blood air barrier is mostly comprised of the alveolar and capillary walls. So the distance between the alveolar air and the blood is very small.
This means the gas takes a shorter time to get through (so fast rate of diffusion)
How does the pressure difference affect the rate of diffusion?
If there is low oxygen in the blood and high oxygen in the alveoli then the rate of diffusion will be very high (eg. during excersise).
So the greater the concentration gradient, the faster diffusion occurs
How does excersise affect blood oxygen
Low activity:
- reduced oxygen consumption
- higher levels of oxygen in the blood
- movement of oxygen into the blood is low but that’s fine because ist not getting used up
High activity:
- increased oxygen consumption
- lower levels oxygen in the venous blood
- diffusion happens very fast to try and deoxygenate blood
Describe how gas diffuses down its pressure gradient
There is a thin barrier, and the surface area is maximised as the capillary wraps around the alveoli.
- So when there is a big difference between blood O2 ad alveoli O2 it will move in very fast, but by the end of the contact, it should be similar levels and then it doesn’t matter if O2 is crossing the barrier or not because they have the same amount of O2
Is everything the same but the opposite for CO2?
Yes
