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USMLE Respiratory > Embryology > Flashcards

Embryology Flashcards

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USMLE® Step 1 flashcards
1
Q

Where does lung development occur / what does it begin with?

A

Formation of lung bud from distal end of respiratory tract

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2
Q

When does the formation of the lungs start?

A

During week 4 of development

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3
Q

What are the 5 stages of lung development?

A

Every Pulmonologist Can See Alveoli

  • Embryonic (wk 4 - 7)
  • Pseudoglandular (wk 5 - 17)
  • Canalicular (wk 16 - 25)
  • Saccular (wk 24 - birth)
  • Alveolar (wk 36 - 8 years)
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4
Q

Errors at what stage of lung development can lead to a tracheoesophageal fistula (TEF)?

A

Embryonic (weeks 4 - 7)

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5
Q

Describe the embryonic stage (wks 4 -7) of lung development?

A

Lung bud -> trachea -> bronchial buds -> mainstream bronchi -> tertiary (segmental) bronchi

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6
Q

Describe the pseudoglandular (wks 5 - 17) stage of lung development

A

Endodermal tubules -> terminal bronchioles.

- Surrounded by a modest capillary network

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7
Q

Describe the Canalicular (wks 16 - 25) stage of lung development

A

Terminal bronchioles -> respiratory bronchioles -> alveolar ducts
- Surrounded by prominent capillary network

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8
Q

Describe the Saccular (wks 24 - birth) of lung development

A

Alveolar ducts -> terminal sacs

- Separated by primary septae

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9
Q

Describe the alveolar stage (wks 36 - 8 years) of lung development

A
  • Terminal sacs -> adult alveoli (due to secondary separation)
  • In utero “breathing” occurs via aspiration and expulsion of amniotic fluid, increasing pulmonary resistance thru gestation
  • At birth, air replaces fluid, decreasing pulmonary vascular resistance
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10
Q

What is pulmonary hypoplasia associated with (2 things)?

A
  • Congenital diaphragmatic hernia (usually left-sided)

- Bilateral renal agenesis (Potter sequence)

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11
Q

What are bronchiogenic cysts caused by?

A

Abnormal budding of the foregut and dilation of terminal or large bronchi

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12
Q

What will a bronchiogenic cyst look like on CXR?

A

Discrete, round, sharply defined, fluid-filled densities on CXR (air filled if infected)

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13
Q

What are the complicatons, if any of bronchogenic cysts?

A

Generally asymptomatic

Can drain poorly
- Airway compression, recurrent resp infections

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14
Q

Where are club cells located and what do they secrete?

A

Bronchioles

  • Surfactant like substance
  • Degrade toxins Cytochrome P-450
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15
Q

What are type 1 pneumocytes?

A

Squamous

  • 97% of alveolar surface
  • Thinly line alveoli
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16
Q

What are the 2 main functions of type 2 pneumocytes?

A
  • Stem cell precursors for type 1 and 2 cells, proliferate during lung damage
  • Secrete surfactant from lamellar bodies
17
Q

What are the functions of surfactant on the lung?

A
  • Decrease alveolar surface tension
  • Decrease alveolar collapse
  • Decrease lung recoil
  • Increase compliance (able to be inflated)
18
Q

What is surfactant composed of?

A

Multiple lecithins, mainly dipalmitoylphosphatidylcholine (DPPC)

19
Q

When does surfactant synthesis occur and when are mature levels of surfactant achieved?

A
  • Synthesis ~ 20 weeks gestation

- Mature levels ~ 35 weeks gestation

20
Q

What are important molecules in surfactant synthesis and lung development?

A

Corticosteroids

21
Q

What type of alveolar macrophages may be found in HF, Pulm oedema, alveolar hemorrhage?

A

Hemosiderin-laden macrophages

22
Q

What is Neonatal Respiratory distress syndrome and describe the pathophysiology

A

Surfactant deficiency

  • > Incr surface tension
  • > Alveolar collapse (‘ground glass appearance on lung fields)
23
Q

What is seen on CXR in Neonatal Respiratory distress syndrome

A

ground glass appearance on lung fields

24
Q

What are risk factors for Neonatal respiratory distress syndrome?

A
  • Prematurity
  • Diabetes during pregnancy (incr fetal insulin)
  • C-section delivery (decr fetal glucocorticoids as less stressful)
25
Q

What is the treatment of Neonatal Respiratory distress syndrome?

A
  • Maternal steroids pre birth

- Exogenous surfactant for infant

26
Q

What can supplemtal O2 result in for a neonate?

A

RIB

  • Retinopathy of prematurity
  • Intraventricular hemorrhage
  • Bronchopulmonary dysplasia
27
Q

The ratio of what 2 proteins is measured in the amniotic fluid to screen for fetal lung maturity? Explain the ratio

A

Lecithin and sphingomyelin

  • L/S ratio
  • > 2 is healthy
  • < 1.5 predictive of NRDS
28
Q

Persitantly low O2 in NRDS is a risk for what condition?

A

PDA

29
Q

What is the equation for working out collapsing pressure?

A

2 x (surface tension)/ radius

30
Q

What is the Law of Laplace?

A

Alveoli have increased tendency to collapse on expiration as radius decreases

(think collapsing pressure equation)
2 x (surface tension) / radius

USMLE Respiratory (7 decks)

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