Week 10 - Anatomy & Mechanics Of Breathing

Question 1

Describe the anatomy of the lungs

Answer 1

• located in thorax
• extend from neck to diaphragm
• has 3 surfaces
  Diaphragmatic surface (base) - sits on diaphragm
  Costal surface - lies adjacent to ribs
  Mediastinal surface - faces the mediastinum (inwards)

Question 2

Describe the anatomy of the right lung

Answer 2

• wider and shorter than left lung
• has three lobes (superior, middle, inferior)
• has 2 fissures (oblique, horizontal)

Question 3

Describe the anatomy of the left lung

Answer 3

• narrower and longer than right lung
• two lobes (superior + inferior)
• one fissure (oblique)

Question 4

What is the lung hilum?

Answer 4

• located on mediastinal surface
• area where pulmonary vessels, bronchi, bronchial vessels, lymphatics and nerves enter / leave the lung

Question 5

What are some physical properties of the lungs?

Answer 5

Compliance (distensibility)
- the ability of the lungs to expand
- affected by :
- connective tissue structures of lungs
- level of surfactant
- mobility of the thoracic cage

Elasticity
- elastic tissue allows lung expansion during inspiration + recoil during expiration

Question 6

What is the difference between the visceral and parietal pleura?

Answer 6

• visceral pleura adheres directly to the lung
• parietal pleura attaches to the thoracic wall and diaphragm
• pleural cavity = potential space between parietal and visceral layers - contains thin layer of serous fluid

Question 7

What are the functions of the pleura?

Answer 7

• reduce friction during breathing
• creates a pressure gradient which assists in ventilation
• compartmentalises lungs - reduces infection spread

Question 8

What 3 elements make up the bony thorax?

Answer 8

• sternum
• ribs (12 pairs)
• thoracic vertebrae (12)

Question 9

What 3 elements make up the sternum?

Answer 9

• manubrium
• body
• xiphisternum

Question 10

What are the 3 types of intercostal muscle?

Answer 10

• external intercostal muscle
• internal intercostal muscle
• innermost intercostal muscle

(IM’s span the spaces between ribs - intercostal spaces)

Question 11

What is the difference in fibre direction between external and internal intercostals?

Answer 11

Externals - fibres run downwards and forwards
Internals - fibres run downwards and backwards

Question 12

Describe some features of the diaphragm

Answer 12

• separates thorax from abdomen
• Innervated by phrenic nerve
• fibrous pericardium fused to central tendon
• openings for inferior vena cava, oesophagus + aorta
• attatched to xiphisternum, costal margin, 11th + 12th ribs, and lumbar vertebrae

Question 13

What is the difference between inspiration and expiration?

Answer 13

• Inspiration = movement of air into lungs, caused by intrapulmonary pressure being lower than atmospheric pressure
• expiration = movement of air out of lungs, caused by intrapulmonary pressure being higher than atmospheric pressure

Question 14

how can thoracic volume be changed?

Answer 14

Altering:
- vertical diameter
- anterior posterior (AP) diameter
- transverse diameter

Question 15

How do you alter vertical diameter of lungs?

Answer 15

• contraction of diaphragm increases vertical diameter
• relaxation of diaphragm decreases vertical diameter
• diaphragm sort of like an elastic band - when contracted, goes flat and tight - when relaxed, goes loose and curves upwards

Question 16

How do you alter AP + transverse diameters?

Answer 16

• elevate ribs to increase AP + transverse diameters
• lower ribs to decrease AP + transverse diameters

Question 17

What are the muscles of quiet inspiration?

Answer 17

• external intercostals
• diaphragm

Question 18

What are the muscles of quiet expiration?

Answer 18

Passive process - diaphragm and intercostal muscles relax

Question 19

What are the muscles involved in forced inspiration?

Answer 19

• pectoralis (major + minor)
• sternocleidomastoid
• serratus anterior
• scalenes

Question 20

What are the muscles involved in forced expiration?

Answer 20

• inner intercostal
• rectus abdominis
• external oblique
• transversus abdominis
• internal oblique

Question 21

What is respiration?

Answer 21

• exchange of gases (O2 & CO2) between atmosphere, blood, and cells

Question 22

What are the 3 steps of respiration?

Answer 22

• pulmonary ventilation - inspiration and expiration of air between atm and lungs
• external (pulmonary) respiration - exchange of gases between alveoli and blood in pulmonary capillaries
• internal (tissue) respiration - exchange of gases between blood & tissue cells - cells use oxygen for respiration and generate CO2

Question 23

What is Boyle’s Law?

Answer 23

When the temperature of a gas is constant, the pressure of the gas varies inversely with volume

E.g. if volume halves, pressure doubles (if temp is the same)

Question 24

What is intraplueral pressure?

Answer 24

• pressure within pleural cavity
• created by elastic recoil of lungs

Question 25

what is lung (pulmonary) compliance?

Answer 25

The ease with which the lungs can be expanded - depends on 3 factors: - elasticity of lung tissue - connective tissue structure - mobility of chest wall - surface tension

Question 26

What is elasticity of lung tissue?

Answer 26

- measure of elastic recoil - measure of lung volume changes resulting from a given pressure change - calculated by equation Compliance = dV / dP ( dV = difference in volume, dP = difference in pressure) Units = litres/cmH2O)

Question 27

How does surface tension affect lung compliance?

Answer 27

- the greater the surface tension, the lower the compliance (makes inspiration more difficult)

Question 28

How does pulmonary surfactant affect surface tension?

Answer 28

- greatly reduces surface tension, which in turn increases compliance - equalises pressure differences between small + large alveoli

Question 29

What is neonatal respiratory distress syndrome?

Answer 29

- lack of surfactant secretion in premature babies - causes reduced compliance, cause alveoli to collapse upon exhalation - 50% die without rapid treatment

Question 30

How is airway resistance measured?

Answer 30

- forced vital capacity (FVC) + forced expiratory volume in 1 second (FEV1) - FVC = forcibly breathing out vital capacity - FEV1 = the volume of air expired in 1 second

Question 31

What is the function of a spirometer?

Answer 31

To measure lung volumes and capacities E.g. tidal volume, vital capacity, etc

Question 32

What is tidal volume? (TV)

Answer 32

- volume of air inhaled or exhaled in one quiet breath - males = 500mls, female = 500mls

Question 33

What is expiratory reserve volume? (ERV)

Answer 33

- the amount of air the can be forcibly exhaled after a normal tidal volume exhalation - males = 1000mls, female = 700mls

Question 34

What is inspiratory reserve volume? (IRV)

Answer 34

- the amount of air that can be forcibly inhaled after a normal tidal volume inhalation - males = 3300mls, females = 1900 mls

Question 35

What is residual volume? (RV)

Answer 35

- air remaining in lungs after maximum expiration - males = 1200mls, females = 1100mls

Question 36

What is vital capacity? (VC)

Answer 36

- the maximum amount of air that can be expired after a maximum inspiratory effort VC = TV + IRV + ERV Males = ~4800ml, female = ~4200ml

Question 37

What is inspiratory capacity (IC)

Answer 37

- the maximum amount of air that can be inspired after a normal expiration - IC = TV + IRV

Question 38

What is functional residual capacity? (FRC)

Answer 38

- the volume of air remaining in the lungs after a normal tidal expiration - FRC = RV + ERV

Question 39

What is the total lung capacity? (TLC)

Answer 39

- the maximum amount of air contained in the lungs after a maximum inspiratory effort - TLC = TV + IRV + ERV + RV - males = 6000ml, females = 4200ml

Question 40

What is the difference between pulmonary and alveolar ventilation?

Answer 40

- pulmonary volume includes all air inhaled - however, for every 500ml tidal volume, 150ml doesn’t reach alveolar exchange surfaces - due to air in ‘dead space’ - air that doesn’t participate in gas exchange

Question 41

How is alveolar ventilation calculated?

Answer 41

Respiratory rate x (TV - anatomical dead space) E.g. 12 x (500 - 150) = 4.2 litres min-1