Lesson 10: Gas Exchange Flashcards
how goes gas exchange at the lungs happen?
via diffusion (passive)
what are some things that can cause issues with diffusion of gases?
- if the space between the alveoli and the capillary is too big (thicker space)
the partial pressures of what are key for understanding gas exchange efficiency and gas transport?
oxygen and co2
the concentration of of O2 and CO2 is dependent on?
the pressure
what is the equation for calculating partial pressure?
total pressure x gas fraction
is pressure higher or lower as you get higher?
lower. less pressure pushing down on you
true or false: the concentration (gas fraction) of oxygen in the room is the same as the concentration of oxygen on the peak of Mount Everest?
true
why do people need oxygen tanks when they go climb mount everest to keep their oxygen and blood oxygen levels if the gas fraction is always the same?
they need to overcome the partial pressure drop
atmospheric air is composed of? (the air we inhale)
nitrogen oxygen and co2 predominantly.
- 79.04% nitrogen
- 20.93% oxygen
- 0.03% CO2
when the cabin pressure is lost in an airplane, they give you masks. what does the oxygen mask do?
its supplemental oxygen to help get our partial pressure up. its 80-100% oxygen. (atmospheric pressure stays low so we need to higher oxygen fraction)
what is our PO2 at sea level?
760 mmHg x 0.2093 = 159 mmHg
(much lower on Mount Everest)
what do you need to do if you want to increase the partial pressure of O2?
you need to increase the oxygen fraction (that is why people need oxygen tanks when they climb mount everest.)
expired air is composed of?
- 79.95% nitrogen
- 15.85% oxygen
- 4.2% CO2
what does it represent when you have exhaled less oxygen than what you have taken in?
represents that you have taken oxygen, deliver it, and consume some of it to create ATP for cellular function
what does it represent when you have exhaled more co2 than what you have taken in?
represents metabolic CO2 productive
- throughout the tissues you have internal cellular respiration
what does our expired airs composition depend on?
physiological state
- exercising, resting, etc.
Therefore, we cannot measure expired partial pressures unless given the gas fractions.
what is our window of regulated arterial PCO2 value?
36-40mmHg
what pressure difference in what is what helps to facilitate diffusion?
pressure differences in the alveoli and the capillaries
what is Henrys Law?
the volume of gas dissolved in a liquid is proportional to the partial pressure of the gas
what is the equation to solve for concentration of gas in a liquid (ml/dl)?
Pgas x k
what is ‘k’?
solubility coefficient of the gas in the liquid
why does O2 and CO2 have different solubility coefficients?
because their partial pressure gradients/concentration gradients in the capillaries and the alveoli are smaller than it is for oxygen
what would happen if CO2 and O2 had the exact same solubility coefficients?
we would have issues with dissolving and thus diffusion and transport of O2 and CO2
** Higher K (solubility coefficient of the gas in the liquid) means?
less pressure required to dissolved gas
what is PaO2?
the arterial partial pressure of O2
what is PAO2?
its the partial pressure in alveolar O2
what is PvO2?
the venous partial pressure of O2
*** what is the partial pressure of oxygen in the alveoli?
generally about 100mmHg
what is the PO2 in the venous circulation?
about 40, lower than the alveolar so diffusion happens because of the gradient
assuming that we have perfect levels of diffusion in the lungs, what is the arterial PO2?
the same as the alveolar PO2 in the setting of a normal lung
in what scenario will there be a difference in the alveolar and arterial PO2?
interstitial lung disease
- any disease that will affect the rate of diffusion
what PCO2 in the arterial blood is?
about 40mmHg
what is PCO2 in the venous blood?
about 46mmHg or higher
we can change PO2 and PCO2 a lot through?
ventilation
what is hyperventilation?
- over ventilation
- ventilation > CO2 production (causing a decrease in arterial PCO2, and increase your arterial PO2 because you are overbreathing)
- different than higher in respiration that occurs with exercise
how is hyperventilation different from over breathing during exercise?
because it is called hyperpnea during exercise
- ventilation is directly proportional to CO2 and O2 production so it does not affect homeostasis. Arterial blood gas values will stay the exact same.
what is hypoventilation?
- under ventilation
- ventilation < CO2 production
how does decreased PO2 in inspired air (altitude) affect PAO2 and PaO2?
decreases it
- it is going down because atmospheric pressure does down as altitude goes up
how does increasing alveolar ventilation and unchanged metabolism affect PAO2 and PACO2?
- increase PO2, decrease PCO2
how does increasing metabolism and unchanged ventilation affect PAO2 and PACO2?
decrease O2, increase CO2 (when you do not breathe, your CO2 accumulates)
how does increasing your metabolism and ventilation (VA) affect PAO2 and PACO2?
(you are exercising)
- there is no change, they both rise in perfect synchrony
- blood gas remains
where does blood need to go so that gas exchange can occur?
the capillaries to be perfused
what is ventilation perfusion matching?
the matching of the airway, the airflow to the alveoli and the blood flow to the capillary or to the tissue
what is perfusion?
blood flow to a tissue or an organ
its the relationship between what that allows us to have hopefully perfect gas exchange?
ventilation and perfusion
- disturbance in the relationship = alter gas exchange
how is ventilation:perfusion affected with a shunt (no air flow, but has blood flow)?
the blood does not get oxygenated, so V/Q = 0/1 and PaO2 is low
how is ventilation:perfusion affected with pure dead space (air flow, but has no blood flow)?
V/Q = 1/0. no blood to get oxygenated.
- increase alveolar and plus physiological dead space
- ventilation goes down to take place in gas exchange with the capillaries but there is no blood flow there available. so the ventilation/gas in there doesn’t take place in gas exchange. wasted
Why don’t we just breath more faster so we get more intake or oxygen?
Our oxygen levels are exactly where we need it to be. Breathing more will have 0 physiological benefit for us.
