Respiratory System - Mechanics of Breathing

Question 1

What are the accessory muscles of inspiration?

Answer 1

Sternocleidomastoid - elevates sternum
Scalenes - anterior, posterior and middle, elevate and fixes upper ribs

Question 2

What are the principal muscles of inspiration?

Answer 2

External intercostals - elevate ribs, increase width of thoracic cavity
Interchondrial part of internal intercostals - elevates ribs
Diaphragm - domes descend, increasing vertical dimension of thoracic cavity

Question 3

What are the muscles of expiration?

Answer 3

Quiet breathing - expiration results from passive recoil of lungs and rib cage
Active breathing - relaxation of muscles
Internal intercostals except interchondrial
Abdominals - push diaphragm up
Rectus abdominis
External and internal oblique
Transversus abdominis.

Question 4

Describe the structure of the respiratory system.

Answer 4

Upper respiratory tract - nasal cavity, pharynx and larynx.
Lower respiratory tract - trachea, bronchi and lungs

Question 5

What are the movements of breathing for ventilation?

Answer 5

Ventilation - inspiration and expiration
Inspiration requires a negative pressure within alveoli
Expiration requires a positive pressure within alveoli
Respiratory muscles are able to generate that sucking and blowing pressure automatically

Question 6

Define elastic recoil of the lungs.

Answer 6

Quiet breathing
Expiration depends on lung elasticity - elastin in lung
Elastic recoil resists stretch making expiration automatic
Lungs tend towards their smallest volume
Destruction of these elastic fibres causes emphysema

Question 7

Give approximate normal values for lung pressures during quiet breathing

Answer 7

Intra-alveolar pressure = 0 mmHg
Intra-pleural pressure = -4 mmHg

Question 8

Give approximate normal values for lung pressures
during inspiration

Answer 8

Intra-alveolar pressure = -1 mmHg
Intra-pleural pressure = -6 mmHg

Question 9

Give approximate normal values for lung pressures
during expiration

Answer 9

Intra-alveolar = +1 mmHg
Intra-pleural = -4 mmHg

Question 10

What is the pleura?

Answer 10

Consists of parietal pleura, pleura cavity and visceral pleura
Function is to stick lungs to the chest wall
Negative intra-pleural pressure helps this function
Pleural fluid in the pleural cavity aids movement via lubrication

Question 11

Describe the velocity of gas in the lungs.

Answer 11

Highest velocity in the trachea
Smallest velocity in the small airways like alveolus
Laminar flow describes small and slow air flow
Turbulent flow describes fast and air flow

Question 12

How do you measure lung volumes?

Answer 12

Lung volumes are measured by spirometry

Question 13

Define;
Total lung capacity
Functional residual capacity
Residual volume
Inspiratory capacity
Expiratory reserve volume
Vital capacity

Answer 13

Total lung capacity - volume at the end of maximal inhalation
Functional residual capacity - volume at the end of normal inhalation
Residual volume - volume at the end of maximal exhalation
Inspiratory capacity - volume between FRC and TLC
Expiratory reserve volume - volume between FRC and RV
Vital capacity - volume of gas exhaled from TLC to RV

Question 14

Define airway resistance to flow.

Answer 14

Refers to the hindrance or opposition encountered by the movement of air through the respiratory passages during breathing
Determined by the combined effects of various factors such as the size and length of the airways, the viscosity of the air, and the rate of airflow.
Poiseuille’s law, which states that the resistance of a tube to flow is inversely proportional to the fourth power of its radius so a small change in airway diameter can significantly affect airway resistance