CVPR First Aid: Respiratory embryology Flashcards
Describe lung development
Occurs in 5 stages Initial development of lung bud from distal end of respiratory diverticulum during week 4 Every Pulmonologist Can See Alveoli
Stages of lung development mnemonic
Every Pulmonologist Can See
Alveoli Embryonic Pseudoglandular Canalicular Saccular Alveolar
The embryonic stage of lung development occurs during
4-7 weeks
Describe the embryonic stage of lung development
Lung bud → trachea → bronchial buds → mainstem bronchi → secondary (lobar) bronchi → tertiary (segmental) bronchi
Embryonic stage of lung development key features
Errors at this stage can lead to tracheoesophageal fistula
The pseudoglandular stage of lung development occurs during
5-17 weeks
Describe the pseudoglandular stage of lung development
Endodermal tubules → terminal bronchioles Surrounded by modest capillary network
Pseudoglandular stage of lung development key features
Respiration impossible Incompatible with life
The Canalicular stage of lung development occurs during
16-25 weeks
Describe the canalicular stage of lung development
Terminal bronchioles → respiratory bronchioles → alveolar ducts Surrounded by prominent capillary network
Canalicular stage of lung development key features
Airways increase in diameter Respiration capable at 25 weeks Pneumocytes develop starting at 20 weeks
Errors at this stage can lead to tracheoesophageal fistula
Embryonic stage of lung development 4-7 weeks
The saccular stage of lung development occurs during
Week 26-birth
Describe Saccular stage of lung development
Alveolar ducts → terminal sacs Terminal sacs separated 1° septae
The alveolar stage of lung development occurs during
36 weeks to 8 years
Describe the alveolar stage of lung development
Terminal sacs → adult alvoeli (due to 2° septation) In utero “breathing occurs via aspiration and expulsion of amniotic fluid → ↑ vascular resistance through gestation At birth fluid gets replaced with air → ↓ in pulmonary vascular resistance
Describe the key feature of the alveolar stage of lung development
At birth: 20 - 70 million alveoli By 8 years: 300 - 400 million alveoli
Lung development diagram
642
List of congenital lung malformations
Pulmonary hypoplasia Bronchogenic cysts Club cells
What is pulmonary hypoplasia
Poorly developed bronchial tree with abnormal histology
Pulmonary hypoplasia is associated with
Congenital diaphragmatic hernia (usually left-sided)
Bilateral renal agenesis (Potter sequence)
What are Bronchogenic cysts?
Discrete, round, sharply defined, fluid-filled densities on CXR (air-filled if infected) caused by abnormal budding of the foregut and dilation of terminal or large bronchi Generally asymptomatic but can drain poorly, causing airway compression and/or recurrent respiratory infections
Describe Type II pneumocytes
- Secrete surfactant from lamellar bodies → ↓ alveolar surface tension which prevents alveolar collapse ↓ lung recoil ↑ compliance
- Cuboidal and clustered
- Serve as precursors to Type I pneumocytes and other Type II cells
- Proliferate during lung damage
Bronchogenic cysts are caused by?
Caused by abnormal budding of the forgut and dilation of terminal or large bronchi
Symptoms of bronchogenic cysts
Generally asymptomatic but can drain poorly, causing airway compression and/or recurrent respiratory infections
What are club cells?
Nonciliated; low columnar/cuboidal with secretory granules located in the bronchials Degrade toxins; secrete component of surfactant Act as reserve cells
List of alveolar cell types
Type I pneumocytes Type II pneumocytes Alveolar macrophages
Describe Type I pneumocytes
97% of alveolar surfaces Line the alveoli Squamous; thin for optimal gas diffusion
Importance of surfactant to the alveoli
Secrete surfactant from lamellar bodies → ↓ alveolar surface tension which prevents alveolar collapse ↓ lung recoil ↑ compliance
Collapsing pressure = 2(surface tension) / radius
Alveoli have ↑ tendency to collapse on expiration as radius is lower ↓ (law of Laplace)
When does surfactant synthesis begin?
≈ week 20 of gestation But mature levels are not achieve until around week 35
Corticosteroids and lung development
Corticosteroids are important for surfactant production and lung development
What is surfactant composed of?
Pulmonary surfactant is a complex mix of lecithins, the most important of which is dipalmitoylphosphatidylcholine (DPPC)
Describe alveolar macrophages
Phagocytose foreign materialls
Release cytokines and alveolar proteases
Hemosiderin-laden macrophages may be seen in pulmonary hemorrhage
What is neonatal distress syndrome?
Surfactant deficiency → ↑ surface tension → alveolar collapse
Neonatal distress syndrome imaging
Ground-glass appearance on CXR
Risk factors of neonatal distress syndrome
3 listed
- Prematurity
- Maternal diabetes (due to ↑ fetal insulin)
- C-section delivery (↓ release of fetal glucocorticoids: less stressful than vaginal delivery)
Complications of neonatal distress syndrome
PDA
Necrotizing enterocolitis
Treatment of neonatal distress syndrome
- Maternal steroids before birth
- Exogenous surfactant for infant
- Therapeutic O2 can result in (RIB)
- Retinopathy of prematurity
- Intraventricular hemorrhage
- Bronchopulmonary dysplasia
Screening tests for fetal lung maturity
- Lecithin-sphingomyelin (L/S) ratio in amniotic fluid (≥ 2 is healthy; < 1.5 is predictive of NRDS)
- Foam stability index
- Surfactant-albumin ratio
Describe the main zones of the respiratory tree
Conducting zones
Respiratory zones
Conducting zones
Large airways consist of
Nose
Pharynx
Larynx
Trachea
Bronchi
Area of greatest resistance in the respiratory tree
Tertiary bronchioles
Area of least resistance in the respiratory tree
Terminal bronchioles because large numbers in parallel (1/R)
Small airways consist of?
Bronchioles that further divide into terminal bronchioles
Function of the conducting zone of the respiratory tree
Warms
Humidifies
Filters air but does not participate in gas exchange = anatomical dead space
Cartilage and goblet cells extend to the end of the bronchi
Lung cellular content
Pseudostritified ciliated columnar cells primarily make up the epithelium of bronchus and extend to the beginning of terminal bronchioles, then transition to cuboidal cells which clear mucus and debris from the lungs (mucociliary escalator)
Airway smooth muscle cells extend to the end of terminal bronchioles (sparse beyond this point)
Describe the respiratory zone of the respiratory tree
Lung parenchyma; consists of respiratory bronchioles, alveolar ducts and alveoli
Participates in gas exchange
Mostly cuboidal cells cuboidal cells in respiratory bronchioles, then simple squamous cells up to alveoli
Cilia terminate in respiratory bronchioles
Alveolar macrophages clear debris and participate in immune response
Respiratory tree diagram
644
Lung lobes
Right lung has 3 lobes
Left lung has 2 lobes and lingula
What is a lingula
The homolog of the right middle lobe in the left lung, instead of a middle lobe the left lung has a space occupied by the heart
Describe the relation of the pulmonary artery to the bronchus at each lung hilum
Described by RALS - Right Anterior, Left Superior
carina location
Carina is posterior to ascending aorta and anteromedial to descending aorta
What is the most common site for inhaled foreign bodies
The right lung because the right main stem is wider, more vertical and shorter than the left
If you aspirate peanut while supine
usually enters the right lower lobe
If you aspirate peanut while laying on the right side
usually enters the right upper lobe
If you aspirate peanut while upright
usually enters the right lower lobe
Lung anatomy pictures
645
Describe structures that perforate the diaphragm
At T8: IVC, right phrenic nerve
At T10: esophagus, vagus (CN 10; 2 trunks)
At T12: aorta (red), thoracic duct (white), azygous vein (blue), “At T-1-2 it’s the red white and blue)
Identify structures that perforate the diaphragm
Describe the innervation of the diaphragm
Diaphragm is innervated by C3, 4 and 5 (phrenic nerve)
Pain from diaphragm (air, blood, pus in peritoneal cavity) can be referred to shoulder (C5) and trapezius ridge (C3, 4)
Structures that perforate the diaphragm mnemonic
Number of levels
T8: Vena Cava
T10: Oesophagus
T12: Aortic hiatus
At T12: aorta (red), thoracic duct (white), azygous vein (blue), “At T-1-2 it’s the red white and blue)
I (IVC) ate (8) ten (10) eggs (esophagus) at (aorta) twelve (12)
Errors at this stage can lead to tracheoesophageal fistula
Embryonic stage
Pneumocytes develop starting at? in what phase?
Pneumocytes develop starting at 20 weeks in the canalicular phase of respiratory development
Respiration capable at? in what phase?
25 weeks
in the canalicular phase
Therapeutic O2 in neonatal distress syndrome can result in?
3 listed
Therapeutic O2 can result in (RIB)
- Retinopathy of prematurity
- Intraventricular hemorrhage
- Bronchopulmonary dysplasia
Persistent low O2 tension →
risk of PDA
