2- Alveolar Gas Exchange Flashcards
(42 cards)
The point of the lungs is to bring ________ and ________ together. The purpose of the _________ is what brings these two things together.
Ventilation (air)
Perfusion (blood)
Alveolus
What are the airways not designed to participate in gas exchange?
Anatomic Dead Space
What’s happening physiologically in the conducting airways?
Air Flow
When air flows through a tube, the airway _________ makes airflow more difficult.
Resistance
***This is the control of bronchiole diameter
If airway resistance is (HIGH/LOW), airflow slows down and takes more muscle effort to produce. If airway resistance is (HIGH/LOW), airflow is fast and easy.
High
Low
What controls the airway resistance? Think of the equation for resistance.
R = 8nL/rˆ4
n = viscosity (for air, this won't change much) L = length of tube r = radius of tube ***Main factor
The control of the bronchiole diameter (airway resistance) is courtesy of the ________ ________ in the airway walls.
Smooth Muscle
Why do we want to change the airway resistance?
– I want to send the air in my lungs to the ‘right’ places. For right now, that means alveoli that have a good blood supply.
This is the volume of air reaching the alveoli.
Alveolar Ventilation
***The amount of air reaching the alveoli every minute is the Minute Alveolar Ventilation
What is the equation for Minute Alveolar Ventilation?
VA(dot) = VA x F
***4 L/min is average value!
Perfusion (Q) is from the _______ _______ and is 5 L blood/min.
Right Ventricle
***Won’t have to calculate this!
What is the equation for the diffusion rate in ml/min of a gas?
J = [ (S.A.) x D x (P1-P2) ] / Distance
J = diffusion rate in ml/min D = diffusion coefficient for each gas (P1-P2) = pressure gradient across alveolar membrane S.A. = surface area available for diffusion Distance = diffusion distance (thickness of alveolar barrier)
***This equation is solved for each gas individually! DO NOT HAVE TO SOLVE!
So how much gas is exchanged every minute? Meaning, what is J (diffusion rate in ml/min)? These values under normal resting conditions are…
250 mL O2 are exchanged every minute.
200 mL CO2 are exchanged every minute.
The diffusion of each gas (O2 and CO2) is __________ of one another.
Independent
What factors in the diffusion rate equation (J) depend directly on the structure of the alveolus?
S.A.
Distance
S.A. in the diffusion rate equation (J) is the surface area available for diffusion. It corresponds to the number of ________ in the lungs.
Alveoli
As surface area increases, J will (INCREASE/DECREASE) and vice versa.
Increase
***This is why patients with emphysema (COPD) have a hard time getting sufficient oxygen into their system. They lost alveoli so their surface area is reduced, thus reducing their diffusion rate.
Distance in the equation refers to the diffusion distance (thickness of alveolar barrier). What all is included as part of the distance?
- Fluid layer
- Alveolar epithelium
- Interstitial space
- Blood vessel wall
As distance increases, J will (INCREASE/DECREASE) and vice versa.
Decrease
The deposition of collagen within the interstitial spaces increases the diffusion distance, which results in a (INCREASE/DECREASE) of the diffusion of the gases across the barrier.
Decrease
***This occurs in people with Interstitial Lung Disease
D is the diffusion coefficient for each gas. D depends on what?
- The solubility of the gas in water (in your body)
- **O2 less soluble in water than CO2
- The molecular weight of the gas.
- **CO2 weighs more than O2
The solubility of CO2 more than counters the difference in molecular weight, so DCO2 is _______ the DO2.
20x
***Means CO2 is way more soluble than O2, so CO2 will cross even if O2 is having a hard time!
If the numbers are positive or negative for the pressure gradient, what does that mean?
Positive = moving in Negative = moving out
An RBC spends about _______ seconds in a pulmonary capillary (under resting conditions).
0.75
