Developmental Aspects of Lung Disease Flashcards
5 phases of structural lung development that occur at progressive times during gestation
- EMBRYONIC (3-8 weeks)
- PSEUDOGLANDULAR (5-17 weeks)
- CANALICULAR (16-26 weeks)
- SACCULAR (24-38 weeks)
- ALVEOLAR (36 weeks - 2/3 years)
Embryonic phase (3-8 weeks) What forms during this phase?
- Occurs within the first month.
- The lung bud called the respiratory diverticulum develops from the fetal foregut.
- By about 5 weeks, two primary lung buds are visible. These later divide into lobar buds (3 on right and 2 on the left)
- Like the gut the cells of lining the lung buds are derived from the endoderm, whereas the bloods vessels and connective tissues surrounding the lungs are derived from the mesoderm
Pseudoglandular phase (5-17) What is formed during this phase?
- Rapid branching of the airways.
- Eventually 16-25 primitive segmental bronchi are formed which is continue to elongation and widen in later phases
- Specialised cells such as cilia and mucous glands also appear the airways
Canalicular phase (16-26) What develops during this phase
The lungs develop their distal architecture.
- this includes the terminal bronchioles, alveolar sacs and capillary blood vessels (which form the gas exchange units).
What appears during CANALICULAR phase?
Both type 1 and type 2 pneumocytes appear.
- Type 1 cells are very thin membrane cells which allow gas exchange
- Type 2 cells produce and store surfactant, a specialized lipoproten, which helps keep the alveoli open.
What is the limit of variability?
In the late stage of the canalicular phase, the presence of these specialized gas exchange units make it is possible for a fetus delivered prematurely to successfully survive with intensive care support.
SACCULAR phase (24-38) What happens during this phase?
- Alveolar sacs which later become alveoli after birth, grow in size and become well-formed.
- In this stage, more surfactant is produced.
- The bronchioles continue to elongate, interstitial tissue between the sacs reduce and the alveolar walls be come thinner which will improve gas exchange.
ALVEOLAR phase (36 weeks - 2/3 years) What happens during this phase?
- The lungs can independent sustain breathing without support.
- Cells at this stage are well differentiated and the pulmonary vasculature more developed forming the final alveolar structure.
Postnatal lung growth
Alveolar septation continue after birth
- The process occurring the alveolar phase continues to occur beyond beyond birth until lungs are fully developed in childhood
Define CONGENITAL ABNORMALITIES
Abnormalities of the airway and lungs present at birth. Most are relatively uncommon.
How are congenital abnormalities picked up? 4 examples
ANTENATAL SCREENING
- Ultrasound
- MRI
NEWBORN
- Tachypnoea
- Respiratory distress
- Feeding issues
CHILDHOOD
- Stridor/wheeze
- recurrent pneumonia
- Cough
- Feeding issues
ASYMPTOMATIC
- Incidental finding
Give 3 examples of common upper congenital abnormalities and 2 examples of lower common congenital abnormalities
UPPER
- Laryngomalacia
- Tracheomalacia
- Traecho-oesphageal fistula
LOWER
- Congenital pulmonary airway malformation (CPAM)
- Congenital diaphragmatic hernia
Laryngomalacia - definition, demographic, clinical presentation, concerns
Dynamic abnormal collapse of larynx
- Commonly seen in infants
- Present with stridor, worse with feeding or when upset/excited
- Will improve within first year
- Concern if affects feeding, growth or causes apnoeas.
Tracheomalacia - definition, demographic, cause?, clinical presentations, management
Dynamic abnormal collapse of tracheal walls
- Can be isolated in healthy infants
- Associated with genetic conditions
- May be caused by external compression (e.g vessels, tumour)
- Presentation:
- Barking cough
- Recurrent “croup”
- Breathless on exertion
- Stridor/wheeze
- Management includes physio and antibiotics when unwell
- Natural history resolution with time
Tracheo-oesphageal fistula - definition, cause?, clinical presentation, treatment, complications
Abnormal connection between trachea and oesphagus
- Majority have associated oesphageal atresia
- Association with genetic conditions
- May be diagnosed antenatally or postnatally
- Presentation:
- Choking
- Colour change
- Cough with feeding
- Unable to pass NG
- Treatment with surgical repair
- Complications include tracheomalacia, strictures, leak and reflux
