2. Mechanics Underlying Ventilation Of The Lung

Question 1

What is the average tidal volume?

Answer 1

400-500ml

Question 2

What is Boyle’s Law?

Answer 2

Inverse relationship between pressure of a gas and volume it occupies

Question 3

What are the lung mechanics in quiet inspiration?

Answer 3

Requires active expansion of thoracic cavity, which in turn expands the lungs
Increase in volume causes decrease in pressure relative to atmosphere
Air is drawn into airways

Question 4

What is the pressure inside the lungs called?

Answer 4

Intrapulmonary pressure

Question 5

What are the lung mechanics in quiet expiration?

Answer 5

Are expelled from airways passively, by relaxing muscles used in inspiration
Reduces volume of thoracic cavity
Reduces volume of lungs, increases pressure inside lungs relative to atmosphere and air expelled

Question 6

What keeps the lungs against the chest wall?

Answer 6

Lungs have natural elastic recoil
Pleural fluid found between visceral and parietal pleura forms seal between lung and thoracic wall because of surface tension

Question 7

What do we call the state when we have just expired and before we start inspiring?

Answer 7

Resting expiratory level

Represents equilibrium between elastic recoil chest outwards and elastic recoil lungs inwards

Question 8

What is the volume at resting expiratory level?

Answer 8

Functional residual capacity

Question 9

What happens during inspiration?

Answer 9

Muscles contract to allow the chest wall and diaphragm to overcome inwards pull of the lung recoil

Question 10

What happens during expiration?

Answer 10

Muscles stop contracting
Chest wall and diaphragm no longer overcome inward pull of lung recoil
Return to resting respiratory level

Question 11

Is the intraplural space negative or positive pressure compared to atmospheric pressure?

Answer 11

Negative at all times

Question 12

What are the accessory muscles of forced inspiration?

Answer 12

Sternocleidomastoid
Scalene muscles
Serratus anterior
Pectoralis major

Question 13

What are the accessory muscles of forced expiration?

Answer 13

Internal intercostals

Abdominal wall muscles

Question 14

When is forced inspiration and expiration used?

Answer 14

During exercise but also when diseases affect the lungs

Question 15

What does tidal volume represent?

Answer 15

The volume of air entering and leaving the lungs in a single breath (during quiet inspiration and expiration)

Question 16

What is the inspiratory reserve volume?

Answer 16

Volume of air you are able to breath in above your tidal volume

Question 17

What is the expiratory reserve volume?

Answer 17

Volume of extra air breathed out after a normal expiration

Question 18

What is the residual volume?

Answer 18

Volume of air that always remains in the lungs

Question 19

What is the functional residual capacity?

Answer 19

Amount of air left in lungs at resting expiratory level

Question 20

What is the inspiratory capacity?

Answer 20

Amount of air we can breath in (tidal volume) plus how much extra air we can inspire extra (inspiratory reserve volume)

Question 21

What is vital capacity?

Answer 21

Amount of air that we can expire after a maximal inspiration

Question 22

What is the total lung capacity?

Answer 22

Vital capacity add residual volume

Question 23

What is the problem with surface tension of fluid?

Answer 23

Limits expansion of alveoli

Decreases compliance making it difficult for alveoli to expand

Question 24

What is surfactant?

Answer 24

Acts to disrupt interaction between fluid molecules on alveolus surface, reducing surface tension
Secreted by type 2 pneumocytes

Question 25

What does reducing surface tension in smaller alveoli do?

Answer 25

Prevents pressure rising within the alveoli as a result of the smaller volume

Question 26

What does surfactant ensure?

Answer 26

Ensures pressures in alveoli do not drop despite increase in size

Question 27

How is the resistance to flow overcome in the airways?

Answer 27

Parallel arrangement of small airways compensates for increase in their individual resistance