CVPR First Aid: Respiratory embryology Flashcards by Jay Sandoval

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

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Stages of lung development mnemonic

Every Pulmonologist Can See

Alveoli Embryonic Pseudoglandular Canalicular Saccular Alveolar

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The embryonic stage of lung development occurs during

4-7 weeks

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Describe the embryonic stage of lung development

Lung bud → trachea → bronchial buds → mainstem bronchi → secondary (lobar) bronchi → tertiary (segmental) bronchi

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Embryonic stage of lung development key features

Errors at this stage can lead to tracheoesophageal fistula

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The pseudoglandular stage of lung development occurs during

5-17 weeks

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Describe the pseudoglandular stage of lung development

Endodermal tubules → terminal bronchioles Surrounded by modest capillary network

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Pseudoglandular stage of lung development key features

Respiration impossible Incompatible with life

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The Canalicular stage of lung development occurs during

16-25 weeks

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Describe the canalicular stage of lung development

Terminal bronchioles → respiratory bronchioles → alveolar ducts Surrounded by prominent capillary network

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Canalicular stage of lung development key features

Airways increase in diameter Respiration capable at 25 weeks Pneumocytes develop starting at 20 weeks

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Errors at this stage can lead to tracheoesophageal fistula

Embryonic stage of lung development 4-7 weeks

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The saccular stage of lung development occurs during

Week 26-birth

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Describe Saccular stage of lung development

Alveolar ducts → terminal sacs Terminal sacs separated 1° septae

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The alveolar stage of lung development occurs during

36 weeks to 8 years

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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

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Describe the key feature of the alveolar stage of lung development

At birth: 20 - 70 million alveoli By 8 years: 300 - 400 million alveoli

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Lung development diagram

642

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List of congenital lung malformations

Pulmonary hypoplasia Bronchogenic cysts Club cells

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What is pulmonary hypoplasia

Poorly developed bronchial tree with abnormal histology

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Pulmonary hypoplasia is associated with

Congenital diaphragmatic hernia (usually left-sided)

Bilateral renal agenesis (Potter sequence)

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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

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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

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Bronchogenic cysts are caused by?

Caused by abnormal budding of the forgut and dilation of terminal or large bronchi

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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

CVPR First Aid: Respiratory embryology Flashcards

(65 cards)