Lungs

Question 1

Components of Respiratory system

Answer 1

• Lungs
• Conducting airways
• Central Nervous system
• Chest wall
• Muscles of respiration

Question 2

Lung structure

Answer 2

• Right - 3 lobes (upper/middle/lower) - divided by horizontal and oblique fissures respectively
  > 10 bronchopulmonary segments
• Left 2 lobes (upper/lower divided by oblique fissure)
  > smaller to make room for heart
  > middle area = lingula area - allows comparison to right lung
  > 8 bronchopulmonary segments (may combine to make 10 for comparison)
• Surrounded by pleura - visceral (outer) and parietal (inner) with fluid between to reduce friction
  > negative pressure between pleura help keep them together and lungs inflated

Question 3

Position of the lungs

Answer 3

Superiorly: ~2.5cm above midline of medial 1/3 clavicle
Anteriorly: 6th costal cartilage ~7cm from midline
Laterally: rib 8
Posteriorly: T2-T10

Question 4

Functions of the lungs

Answer 4

• Gaseous exchange
• produce surfactant (keep alveoli open)
• blood reservoir
• filter (between us + outside world)
• immune system (nose + mouth/mucosal elevator/immune cells)
• pH balance - CO2 levels in body

Question 5

Upper + Lower respiratory tracts

Answer 5

> Upper
- Nose
- Mouth
- Pharynx (throat)
- Larynx (voice box)
(Moisten air/ filter particles/ swallowing/voice)
> Lower
- Trachea
- Primary Bronchi
- Secondary bronchi 
- Tertiary bronchi
- Bronchioles
- Terminal bronchioles
- Respiratory Bronchioles
- Alveolar ducts
- Alveolar sacs

Question 6

Trachea

Answer 6

> immediately below larynx - C6
> 2.5 cm in diameter, 11cm long 
> 15-20 C shaped cartilaginous rings (gap posteriorly for oesophagus flexibility)
> divides into 2 at CARINA = T5 level 
Pathologies
- floppy - no cartilage
- obstruction
- cancer

Question 7

Primary Bronchi

Answer 7

> right and left (separated by carina)
> C shaped cartilaginous supports
> right = larger + at sharper angle
> Access the lungs at HILUM
Pathologies
- obstruction
- cancer

Question 8

Secondary Bronchi

Answer 8

> Lobar ie right has 3, left has 2
Cartilaginous plates for support
Pathologies
- Pneumonia

Question 9

Tertiary Bronchi

Answer 9

> Segmental ie. right has 10, left has 8/9
Cartilaginous plates (less than secondary)
more smooth muscle - support but tension increases resistance to airflow
Pathologies
- Infection = bronchitis

Question 10

Bronchioles

Answer 10

> more smooth muscle than cartilage
Pathologies
- Fibrosing alveolitis
- COPD

Question 11

Terminal bronchioles

Answer 11

> 0.3 - 0.5 mm in diameter
> smooth muscle (regulated by ANS)
Pathologies
- Asthma 
- fibrosis

Question 12

Respiratory bronchioles

Answer 12

> each terminal bronchiole has several respiratory
thin + delicate
no cilia (inflammatory/immune responses only)
Deliver air to gas exchange surfaces

Question 13

Alveolar ducts

Answer 13

> connect respiratory bronchioles to alveoli
Pathologies
- cystic fibrosis
- pneumonia

Question 14

Alveolar sacs (300 million

Answer 14

> gas exchange site (type 1 pneumonocyte - aids gases across membrane
surfactant (type 2 pneumonocyte) - hydrophilic head attracted to wall and pushes open + hydrophobic tail provides dry are for gas exchange
mesh like capillary network
Pathologies
- cystic fibrosis
- pneumonia

Question 15

Collateral Ventilation

Answer 15

> channels between alveoli and respiratory bronchioles

• channel of martin - intrabronchiolar
• channel of Lambert - bronchiole - alveolar
• Pore of kohn - interalveolar
• blockage doesn’t null alveolus

> if alveoli collapse - v.high pressure is needed to re-open which will likely damage other alveoli
RESIDUAL VOLUME - keeps alveoli open with help from collateral channels + surfactant

Question 16

Zones of respiratory tract

Answer 16

Conducting Zone (generations 0-16)
- Trachea - Terminal bronchioles
- no gas exchange
- gas travels by convection
ANATOMICAL DEAD SPACE

Respiratory zone (generations 17-23)
- respiratory bronchioles - alveoli
- gas exchange (large sa)
- gas travels by diffusion
PHYSIOLOGICAL DEAD SPACE

Question 17

Circulatory system of lungs

Answer 17

Pulmonary

• gas exchange
• low pressure - slow speed to maximise exchange

Bronchial

• supplies lung tissue
• low pressure for small vessels (higher than pulmonary)

Question 18

Mechanics of breathing

Answer 18

IN
> diaphragm contracts + flattens (75% of work)
> external intercostals contract - ribs move up + out
forced inspiration: sternocleidomastoid/scalene/pec minor/serratus anterior
OUT
> diaphragm relaxes - increasing pressure
> ext intercostals relax - ribs move down + in
forced expiration: internal intercostals/Transverse thoracis (depress ribs) / abdominals (compress abdomen)

Question 19

Normal breathing

Answer 19

> 12-18 breaths per minute
active inspiration (both voluntary + involuntary control)
passive expiration
ratio of inspiration 1:2 expiration (time to move air)
Tidal volume = air moved in one breath

Both intrapulmonary(within airways) and intrapleural (between membranes) pressure decreases with inhalation and increases with exhalation

Question 20

Compliance

Answer 20

> expandability of lungs
measured as Change in Volume/Change in Pressure
reduced compliance:
- atelectasis - collapse of small airways in an area
- fibrosis - stiffening of lung tissue
- obesity

Question 21

Resistance

Answer 21

> resistance to flow of air
either airway (80%medium,20 small) or tissue resistance
Factors
- lung volume
- contraction of smooth muscle
- obstructions (tumour/sputum)
- tissue resistance (elastic properties of lungs + chest wall)
- type of airflow (due to different pressures
a) Laminar (small airways) - more organised + slow
b) Turbulent (large) - disorganised + faster
c) transitional (medium, branch points) - mix of 2

Question 22

Elastic resistance
Elastic recoil
Work of breathing

Answer 22

> Elastic resistance - measure of work exerted by inspiration muscles to expand lungs
Elastic recoil - ability of lungs to rebound
Work of breathing - physical work of muscles of respiration to overcome resistance (elastic + non-elastic)
- increase with respiratory load due to
a) poor compliance
b) increased resistance
c) respiratory capacity
d) more elastic resistance

Question 23

Ventilation sequence

Answer 23

1. respiratory centre sends message to initiate breath
2. muscles of inspiration begin to contract
3. diaphragm contracts + descends
4. rib cage moves up + out - thoracic volume increases
5. intrapulmonary pressure drops
6. pleural pressure becomes more negative
7. intrapulmonary pressure < atmospheric pressure
8. air is moved into lungs until equilibrium
9. air movement stops
10. respiratory centre stops initiation message
11. respiratory muscles relax
12. diaphragm relaxes + moves up
13. rib cage moves down + in
14. lungs recoil
15. intrapulmonary pressure rises
16. intrapleural pressure = less negative
17. air leaves lungs