Lecture 3 - Lung mechanisms

Question 1

Ventilation

Answer 1

Process of inspiration and expiration

Question 2

Lung volumes

Answer 2

Tidal volume
Residual volume
Inspiratory reserve volume
Expiratory reserve volume 
Total lung volume

Question 3

Tidal volume

Answer 3

Volume of air that enters and leaves the lungs at each breath during normal respiration

Question 4

IRV

Answer 4

Max inspired volume of air

Question 5

ERV

Answer 5

Max expired volume of air

Question 6

Residual volume

Answer 6

Volume of air retained after forced expiration

Question 7

Total lung volume

Answer 7

Vital capacity + RV

Question 8

Lung capacities

Answer 8

Inspiratory capacity
Functional residual capacity
Vital capacity

Question 9

Inspiratory capacity

Answer 9

End of quiet expiration to max inspiration

The volume of air that can be inhaled

Question 10

Functional residual capacity

Answer 10

ERV + RV

Volume of air in lungs after quiet expiration

Question 11

Vital capacity

Answer 11

IC + ERV
(IRV+ TV) + ERV

Volume of air breathed in and out of lungs during forced respiration

Question 12

Anatomical dead space

Answer 12

Air that fills the conducting airways not available for gas exchange

Question 13

Physiological dead space

Answer 13

Anatomical dead space + alveolar dead space

Question 14

Alveolar dead space

Answer 14

Air in alveoli that are not perfused or are damaged. Therefore gas exchange does not occur

Question 15

Tidal volume in terms of anatomical dead space

Answer 15

Anatomical dead space + alveolar ventilation

Question 16

Total pulmonary ventilation (minute volume)

Answer 16

TV x RR

Question 17

Alveolar ventilation

Answer 17

(TV- anatomical dead space) x RR

Question 18

Describe quiet inspiration

Answer 18

1. At the end of quiet expiration the atmospheric pressure = intrathoracic pressure
2. The ribs move laterally and superiorly as the chest expands (30% external intercostal and 70% diaphragm) Muscles contract overcome elastic recoil
3. The pleural fluid ensures that the lungs expand with the thorax
4. Intrapulmonary volume increases and pressure decreases
5. The intrapulmonary pressure is lower than the atmospheric pressure which creates a negative pressure
6. Air is drawn in

Question 19

Boyle’s law

Answer 19

An inverse relationship between pressure and volume of a gas

Question 20

Describe quiet expiration

Answer 20

Air is expelled passively

1. Relaxation of inspiratory muscles so they no longer overcome elastic recoil, reducing the intrathoracic volume and reduces lung volume.
2. The intrapulmonary pressure is greater than the atmospheric pressure so air is drawn out

Question 21

Resting expiratory level

Answer 21

State of equilibrium where all forces are equal and opposite so balance out resulting in no chest wall movement at rest

Creates negative pressure within the intrapleural space

There is a tendency to always want to return to the resting state

Question 22

Forces exerted in the chest wall

Answer 22

Lung elasticity and surface tension - lungs pull in and up
Muscles and fascia - Chest wall pulls out
Passive stretch - Diaphragm pulls down

Question 23

Why is intrapleural space negative?

Answer 23

The elastic recoil of the lung pulls the visceral pleura inwards and the chest wall pulls the parietal pleura outward

Question 24

Breach in pleural seal

Answer 24

Pneumothorax- air is drawn in due to negative pressure

Lung collapse due elastic recoil

Question 25

Accessory muscles of inspiration

Answer 25

SCM
Pectoralis major
Serratous anterior
Scalene muscles

Question 26

Accessory muscles of expiration

Answer 26

Internal intercostal muscles
Innermost intercostal muscles
Abdominal wall muscles - rectus abdominis + EO + IO

Question 27

Compliance

Answer 27

The extent to which the lungs can stretch

Volume change per unit volume change

Question 28

Elastic recoil

Answer 28

The tendency to return to a resting state

Question 29

What determines compliance?

Answer 29

Elasticity of lung tissue
Surface tension of fluid lining the alveoli
Surfactant

Question 30

Surface tension

Answer 30

During respiration, the fluid lining the airways and alveoli must stretch due to the increasing SA

Surface tension resist this as want to achieve minimal SA. Reduces compliance

Question 31

Surfactant

Answer 31

Secreted by type II pneumocytes
Mixture of phospholipids and proteins with detergent properties which floats on fluid

Surfactant molecules between the fluid molecules disrupt the interactions between the fluid molecules

Reduces surface tension
Increases compliance

Ensures that pressure is the same in all alveoli regardless of size

Prevents collapse of small alveoli into big alveoli

Question 32

How does SA affect surface tension

Answer 32

As SA increases, surface tension increases

Surfactant effects decrease therefore surface tension increases as alveoli size increases.

Question 33

When does surfactant have the most effect?

Answer 33

When there is a smaller SA as more molecules are present in a given area

Question 34

Pressure

Answer 34

P= 2T/r

T - Surface tension
r - radius

Question 35

Respiratory distress syndrome

Answer 35

Premature babies under 30 weeks
Do not produce surfactant therefore:
- Decrease in compliance - stiff
- Hard to expand

Question 36

Resistance to flow

Answer 36

Tubes of smaller diameter have a higher resistance to flow
Energy needed to overcome resistance
Small decrease in radius - large increase in resistance (r^4)

Question 37

Parallel lower airways

Answer 37

Numerous small airways running in parallel compensate for the increase in individual resistance

Question 38

Upper respiratory system

Answer 38

Highest resistance as have a serial arrangement
Wider tubes
Cartilaginous rings - reduce compression

Lowest resistance in lower airways except when compressed during forced expiration