Respiratory System 3

Question 1

What can a single tidal volume range in size from?

Answer 1

Residual volume to total lung capacity

Question 2

What is functional residual capacity?

Answer 2

The amount of air in the lungs at the end of a normal (relaxed) expiration

Question 3

What moves air?

Answer 3

A pressure gradient

Question 4

When does air enter the lungs?

Answer 4

Only if alveolar pressure (Pa) is less that atmospheric (barometric) pressure (Pb)

Question 5

When does alveolar pressure become sub-atmospheric?

Answer 5

When thoracic volume increases

Question 6

When does thoracic volume increase?

Answer 6

By the descent of the diaphragm and elevation of the rib cage

Question 7

What is the bulk rate of flow of air (ie the volume per unit time) of air entering or leaving the lungs proportional to?

Answer 7

The difference between atmospheric pressure and alveolar pressure

Question 8

When does air leave the lungs (exhalation)?

Answer 8

If alveolar pressure exceeds atmospheric pressure

Question 9

When does air enter the lungs (inhalation)?

Answer 9

If alveolar pressure is less than atmospheric pressure (provided the glottis is open)

Question 10

What reduces the rate at which the lungs expand or deflate (ie the rate at which air enters or leaves the lungs)?

Answer 10

Any factor that increases resistance to air-flow (R)

Question 11

What’s the airflow/resistance proportionality equation?

Answer 11

Rate of change of volume (bulk flow) = (Pb-Pa)/R

Question 12

What happens to the highly elastic lungs?

Answer 12

They tend to collapse at zero volume which tends to separate the visceral and parietal pleura which reduces intra-pleural pressure (Pip) below atmospheric while simultaneously pulling the ribcage outwards

Question 13

What is a balance between the forces (collapsing lungs and recoiling ribcage) achieved at?

Answer 13

Functional residual capacity (FRC)

Question 14

What force causes the lungs to have a tendency to collapse and what does it arise from?

Answer 14

FL, which arises from the elastic recoil of stretches elastic fibres and the surface tension of wet alveolar cells

Question 15

What force does the chest wall (rib cage and its musculature) experience that causes it to spring outwards, thereby increasing its volume, and where does it arise from?

Answer 15

Fcw, and it arises from stretched tissues in the sterno-costal and costo-vertebral joints

Question 16

What does the collapsing tendency of the lungs to exactly counteract the expanding tendency of the rib-cage do?

Answer 16

Leaves the combined system in an equilibrium position

Question 17

If the pressure in airways is zero, what does this mean?

Answer 17

This unique “neutral” position corresponds to FRC

Question 18

What does the negative sign in the force equation?

Answer 18

Merely a formal statement that the forces operate in different directions

Question 19

What happens when a penetrating injury of the chest wall creates a connection between the atmospheric and the intrapleural space?

Answer 19

The balance of forces which normally occurs in the lungs is destroyed on the affected side

Question 20

What allows the lungs to collapse?

Answer 20

The introduction of air between the pleural membranes interrupts the adhesive forces between water molecules

Question 21

What happens when the lung collapses?

Answer 21

The chest wall recoils outward (ie assumes a slightly increased volume)- exactly as expected from the sign of Fcw in the above equation (Fcw= -FL)