Respiratory Cycle

Question 1

What links the lungs to the chest wall?

Answer 1

Lungs will collapse to a small equilibrium volume
Chest wall will expand to a large equilibrium volume
Equal and opposite force sets the functional residual capacity (FRC)
Lung elastic recoil 0.5kPa⬅️➡️0.5kPa chest wall elastic recoil
Intrapleural pressure= -1kPa
Ppl is more negative than the recoil pressures of eye chest wall and lungs which pulls the structures together

Question 2

Describe inspiration

Answer 2

Inspiration muscle contract increasing thoracic volume
Ppl becomes more negative
Lung distending pressure increases
Lungs inflate
Increase in lung volume causes P(A) to fall below P(B)
Air flows into lungs until P(A)=P(B)

Question 3

What are the muscles of respiration?

Answer 3

External and internal intercostal muscles
Diaphragm
(External and internal oblique, rectus and transverse abdominus)
At rest expiration is passive- elastic recoil

Question 4

How is gas transported in the respiratory system?

Answer 4

Convection- large airways and blood vessels

Diffusion- from alveoli to pulmonary capillaries and from capillaries to tissues

Question 5

What is ficks law of diffusion?

Answer 5

Rate of diffusion= SA x 1/thickness x diffusibility x partial pressure gradient
V=A x 1/T x d x (P1-P2)

Question 6

Describe the diffusibility and partial pressures of oxygen and carbon dioxide

Answer 6

CO2 is roughly 20x more diffusible
Greater partial pressure gradient for oxygen
8kPa for oxygen
1kPa for carbon dioxide

Question 7

Lists the partial pressures of oxygen and carbon dioxide around the respiratory system

Answer 7

In air- PO2- 21kPa
PCO2- 0kPa
Inspiration
Mouth- PO2- 20kPa
PCO2- 0kPa
In conducting zone- same as mouth
Alveolar gas is constant- PO2- 13kPa
PCO2- 5kPa
In mixed venous blood- PO2- 5kPa
PCO2- 6kPa
Blood leaving pulmonary capillaries- same as in alveoli space
Expired air- same as alveoli space

Question 8

Roughly, what volume of air are we adding to our lungs when we inspire?

Answer 8

500ml inspiration

350ml added to about 2.5l already in the alveoli space

Question 9

What factors determine alveolar gas composition?

Answer 9

Metabolism
Inspiration
Alveolar ventilation- volume that takes part in gas exchange

Question 10

Describe the changes in alveolar gas partial pressures

Answer 10

P(A)O2= k x 1/rate of oxygen diffusion
If alveolar ventilation is matched to rate of oxygen diffusion alveolar partial pressure of oxygen will remain constant
P(A)CO2= k x 1/Alveolar ventilation
If alveolar ventilation is matched to the rate of carbon dioxide diffusion the alveolar partial pressure of carbon dioxide will remain constant
The relationship between the alveolar partial pressures of O2 and CO2 are the inverse of each other