Structure of the lungs

Question 1

Trachea overview

Answer 1

• Cartilaginous tube conducting air from larynx to bronchi
• 10cm long
• ~2.5cm diameter, from C6 to T4/5
  disc vertebral levels
• Has “c-shaped” cartilage rings to
  maintain patency
• Posteriorly, smooth muscle called
  trachealis which joins each end of the rings, controls diameter

Question 2

Trachea – surrounding structures

Answer 2

Posterior
* oesophagus
Anterior
* Sternothyroid and sternohyoid muscles
* Thyroid gland
* 1st Cartilage ring is palpable
* Thyroid gland obscures cartilages
2-4
* Brachiocephalic trunk
* Cardiac plexus nerves (sympathetic
and parasympathetic)
* Tracheobronchial nodes
* Manubrium (manubriosternal joint
also marks bifurcation of trachea)

Question 3

Trachea – surrounding structures 2

Answer 3

Lateral -

• Thyroid gland lobes
• Parathyroid glands
• Common carotid arteries
• Aortic arch, common carotid and
  subclavian artery (L)
• Azygous arch, Vagus nerve (R)

Posterolateral -

• Recurrent laryngeal nerves
  At the division into primary bronchi, the carina forms

Question 4

Bronchi

Answer 4

• Continuation of trachea, have smooth muscle and complete cartilage rings
• Right and left main/primary bronchi
• Secondary (lobar) bronchi (3 right, 2 left)
• Tertiary (segmental) bronchi
• Bronchial tree
• Note: bronchi receive blood from bronchial arteries, one right, two left.

Question 5

Bronchioles

Answer 5

• Serial divisions of conducting bronchioles, down to 20-25 generations
• As number increases size individually decreases but total surface area increases
• Then becomes respiratory bronchioles -> alveolar ducts -> alveolar sacs

Question 6

Alveoli

Answer 6

• Pulmonary vasculature branches in a similar fashion to bronchi
• Forms capillary beds around alveoli
• Alveoli are a single cell thick
• This provides a large surface area for efficient gas exchange

Question 7

Histology of respiratory tree - trachea

Answer 7

• Cartilage ossifies due to age
• Respiratory epithelium – which is what?
• Note trachealis muscle (TM)

Question 8

Histology of respiratory tree - bronchi

Answer 8

Question 9

Histology of respiratory tree - bronchiole

Answer 9

• Smooth muscle but no cartilage,
  no glands
• Vascular supply (BV) adjacent
• Still respiratory epithelium
• Surrounding alveoli

Question 10

Histology of respiratory tree – terminal bronchiole

Answer 10

• Lumen on right
• Alternating thick and thin portions
• sparse smooth muscle
• CC = club cells (formerly clara cells)
• Club cells are non-ciliated,
  cuboidal epithelium
• Club cells produce protective
  secretions

Question 11

Histology of respiratory tree – Acini

Answer 11

• Capillaries
• Type I pneumocytes
• Type II pneumocytes (SC = septal
  cell, produce surfactant)
• Alveoli = A

Question 12

Histology of respiratory tree

Answer 12

• The above structures contain
  abundant elastic protein fibres (elastin), although it doesn’t show very well on H&E sections

Question 13

Lungs

Answer 13

• Right and left
• Lobes are visibly defined,
  separated by fissures
• Occupy the lateral parts of the thoracic cavity
• Costal, mediastinal, diaphragmatic surfaces
• Connection via hilum
• Root of lung = vasculature and
  airways entering the lung
• Covered in visceral pleurae

Question 14

Lungs

Answer 14

• Supplied by tertiary bronchi 10 per side
• have surgical relevance, be aware but do not memorise

Question 15

Lungs

Answer 15

• Visceral and parietal pleura
• Small amount of serous pleural
  fluid in fluid cavity
• Note terminology for parietal
  pleura
• This reduces friction during
  breathing

Question 16

Mechanics of breathing

Answer 16

• At rest, inspiration mostly driven by the diaphragm (external intercostal contribute)
• Diaphragm contraction increases thoracic volume, drawing air into the lungs
• Gaseous exchange occurs
• Diaphragm relaxes, thoracic volume falls
  and air is exhaled
• Exhaling at rest is largely passive (elastic recoil)
• Higher demand for O2/CO2 removal can involve accessory muscles
• Smooth movement aided by the pleurae

Question 17

Root of lung

Answer 17

• Main bronchus
• Pulmonary artery (deoxygenated blood to lung)
• Pulmonary vein (oxygenated blood to heart)
• Bronchial arteries – supplying bronchi and structural tissue of lung
• Lymph nodes and vessels

Question 18

Lungs – clinical considerations

Answer 18

• Asthma
• COPD
• Cancer
• Foreign body aspiration
• Pneumothorax/haemothorax Pleurisy
• Cystic fibrosis
• Pneumonia

Question 19

Asthma

Answer 19

• Commonest lung condition
• > 8 million in UK
• Inflammation of airways = reduced diameter
• Allergic/nonallergic/occupational
• Management involves a hierarchy
  of pharmacological treatment
• Salbutamol -> β2 adrenoreceptor agonist = relaxes bronchial smooth muscle

Question 20

COPD

Answer 20

• Chronic obstructive pulmonary disease
• Common
• Biggest risk factor is smoking
• Mucus hypersecretion and alveolar destruction
• Emphysema or chronic bronchitis

Question 21

Cancer

Answer 21

• Bronchial carcinoma (95% of primary tumours)
• Smoking is biggest risk factor
• Often very poor prognosis
• Also, common site for metastatic tumour
• Metastases often via lymphatic spread
• Mesothelioma = affecting pleura - asbestos

Question 22

Foreign body aspiration

Answer 22

• Items have a tendency to the right main bronchus (wider, shorter, more vertical)
• N.B. not all items will be detectable by x-ray
• Bronchoscopy to visualise/retrieve

Question 23

Pneumothorax

Answer 23

• Air in pleural cavity
• “collapsed lung”
• Spontaneous (Tall, thin, male)
• Higher risk in certain syndromes
• Penetrating chest injury or damage to lung

Question 24

Pneumonia

Answer 24

• Infective – bacterial, viral, fungal
• Affect lobe/segment “lobar pneumonia” or multiple
• Often affects those with underlying health conditions or frailty
• Lying supine is a risk factor

Question 25

Cystic fibrosis

Answer 25

• Commonest genetically transmitted disease
• Autosomal recessive 1 in 2000
• Mucous is too thick due to abnormal ionic composition (malfunctioning chloride transporter)