Alveolar Capillary Membrane Surface Area Flashcards
How much surface area of the pulmonary capillaries is available for gas exchange?
70 meters squared
How much alveolar surface is available for gas exchange?
80 meters squared
Can you maintain adequate gas exchange if you lose a large quantity of surface area due to disease processes?
No; must compensate by increasing RR and tidal volume
Can you think of any medical problems acute or chronic that would cause a loss of surface area?
Emphysema, pulmonary edema, atelectasis, pneumonia, pneumothorax and pleural effusion
Would you expect hypoxemia to occur and CO2 retention to occur if surface area was decreased?
Yes
What is the purpose of alveolar type II cells?
Produce surfactant
What is the function of the pores of Kohn?
They are the communication between local alveoli and aid in gas exchange. They are a channel that allows gas to move from one alveoli to another
How can smoking and macrophages together result in the development of emphysema?
Macrophages are debris cleaners and are released when a person smokes. As they are cleaning up debris they release chemicals, which break down alveolar structure and lead to emphysema
What is surfactant, what does it do and why’s it so important in keeping us alive?
Surfactant breaks down or prevents surface tension from overwhelming the alveoli (overwhelming the alveoli would result in them collapsing)
How long do you think you could live without surfactant? What would happen to you if you did not have enough?
We could not live long without it. Alveoli will implode of themselves if there is not enough surfactant, which ultimately results in no gas exchange
An increase in capillary hydrostatic pressure can cause pulmonary edema. What is the mechanism of edema, where does the swelling occur? How does it affect gas diffusion?
Capillaries swell up with too much blood and create pressure, pushing plasma against endothelium and into the basement membrane. The basement membrane becomes thicker so less gas diffusion occurs.
What are the four layers of the alveolar capillary membrane, starting with the surfactant layer?
Surfactant layer, alveolar epithelium, interstitial space and capillary endothelium
What is the connection between surfactant deficiency and the VQ mismatch known as shunting? Describe the cause and effect relationship and the mechanics of it all.
Without surfactant, there is no gas exchange and you don’t get ventilation to that alveolus. It becomes the same value as venous blood
Describe the relation of surfactant deficiency to VQ mismatch and shunting
Without surfactant, the radius becomes smaller and the alveoli will snap shut
Relate and explain the pressure, volume change, critical opening/closing pressure, hypoxemia and work of breathing of an alveolus without surfactant.
Pressure will increase with no volume change until you reach s critical pressure and a bubble forms. When the bubble actually forms is when you start seeing volume expansion and that’s when you reach critical opening pressure. The bubble expands until it collapses, which signifies the critical closing pressure. Once the bubbles close (alveoli collapsing), the surface area for gas exchange decreases and the amount of work to open it increases. Work of breathing becomes harder and gas exchange no longer occurs, leading to hypoxemia
Relate surfactant deficiency to lung compliance change.
Surfactant determines lung compliance and the lungs become very stiff without it
Explain alveolar surface tension change and its relationship to lung volume change between end expiration and end inspiration. Why is surface tension at its lowest at the end of expiration?
During expiration without surfactant, surface tension increases and the smaller the radius. If you add surfactant, the smaller molecules become closer together and repel each other to produce pressure and keep the alveoli open
Describe the interstitial space in its natural state.
Area that separates the basement membrane of alveolar epithelium from the basement membrane of capillary endothelium, and contains fluid
How does an increase in capillary hydrostatic pressure affect the interstitial space?
Hydrostatic pressure increases fluid in the interstitial space and increases the distance oxygen has to travel and decrease diffusion
In a normal healthy state what causes oxygen to diffuse across the alveolar capillary gas exchange membrane?
Hemoglobin affinity and a lower diffusion gradient
List three pathological problems that can increase the thickness of the “alveolar capillary gas exchange membrane.”
Fluid overload and hyler membrane
Fick’s law of diffusion
Vgas = A x D x (P1-P2)
———————-
T
What can cause an increase in hydrostatic pressure?
Over hydration; anything in the left side of the heart fails to function properly and fluid starts to build up
How does fluid in the interstitial space cause hypoxemia?
Capillary hydrostatic pressure in the interstitial space is low. If you increase the pressure, water will leak into the interstitial space. This space will swell up with fluid and accumulate (pulmonary edema). Interstitial space is emptied by the lymph system. Eventually the lymph system cannot keep up, fluid leaks into sir space and into alveoli. During this whole time, you’re getting lower and lower oxygen diffusion. Low oxygen diffusion results in hypoxemia
