RESP-embryology

Question 1

where is the respiratory system derived from?

Answer 1

foregut

Question 2

what does the respiratory system begin as?

Answer 2

as an outgrowth from endodermic foregut, just inferior to the pharynx = tube of endoderm

Question 3

what is the laryngotracheal opening?

Answer 3

The opening that still connects diverticulum to pharynx

Question 4

what is the respiratory bud?

Answer 4

elongated laryngotracheal diverticulum

Question 5

what does the endodermal lining of the laryngotracheal groove give rise to in the 4th week of development?

Answer 5

trachea, bronchi and tracheobronchial tree, glands of larynx

Question 6

what does the splanchnic mesoderm of the laryngotracheal groove give rise to in the 4th week of development?

Answer 6

connective tissue, cartilage and smooth muscle of these structures

Question 7

what happens to the laryngeal groove at the end of the 4th week of develop?

Answer 7

evaginates to form laryngotracheal diverticulum -Elongates distally to form a globular ‘respiratory bud’

Question 8

what does the respiratory bud divide into?

Answer 8

2 outpouchings

-primary bronchial buds

Question 9

what happens to the bronchial buds divide into bronchioles?

Answer 9

they grow into pleura formed by mesoderm

Question 10

what are the 2 types of pleura?

Answer 10

visceral pleura

parietal pleura

Question 11

where is the visceral pleura derived from?

Answer 11

splanchnic mesenchyme

Question 12

where is the parietal pleura derived from?

Answer 12

somatic mesoderm

Question 13

what are the 4 stages of lung maturation?

Answer 13

• pseudoglandular
• canalicular
• terminal sac
• alveolar

Question 14

which weeks of development is the pseudoglandular stage?

Answer 14

6-16 weeks

Question 15

which weeks of development is the canalicular stage?

Answer 15

16-26 weeks

Question 16

which weeks of development is the terminal sac stage?

Answer 16

26 weeks to birth

Question 17

which weeks of development is the alveolar stage?

Answer 17

32 weeks to 8 years old

Question 18

describe the events of the pseudoglandular stage?

Answer 18

-Epithelial tubes lined with cuboidal epithelial
cells
-all major elements have formed, except those involved in gas exchange
-Respiration is NOT POSSIBLE, foetuses
born at this stage unable to survive

Question 19

what do the developing lungs resemble in the pseudoglandular stage?

Answer 19

exocrine glands

Question 20

describe the events of the canalicular stage?

Answer 20

• Lumen of bronchi + terminal bronchioles
become larger
• tissue becomes highly vascularised
• By 24 weeks = terminal bronchiole gives
rise to 2 or more respiratory bronchioles but cannot be used due to lack of surfactant
(Divide to form primordial alveolar ducts)
• Respiration IS POSSIBLE because of
primordial alveolar sacs and vascularisation

Question 21

describe the events of the terminal sac stage?

Answer 21

• More terminal sacs develop
• Epithelia becomes a lot thinner to become more closely related to alveolar capillaries
• Adequate gas exchange can now take place
if fetus is born at 26+ weeks
• Type II pneumocytes form

Question 22

what do type 2 pneumocytes secrete?

Answer 22

surfactant

Question 23

describe the events of the alveolar stage?

Answer 23

• Sacs comparable to alveoli are present at 32
weeks
• Epithelial lining becomes a thin, squamous
epithelial layer – type I pneumocytes
• Adjacent capillaries bulge into alveolar
saccules
• By late fetal stage, lungs are capable of
respiration because alveolar capillary
membrane is sufficiently thin to allow gas
exchange

Question 24

what is the size increase of the lungs postnatally due to?

Answer 24

due to the number of respiratory bronchioles and alveoli increasing, NOT because the existing amount increase in size

Question 25

what is lung surfactant?

Answer 25

Lipoprotein produced by Type II Pneumocytes during the Canalicular Stage (16-26 weeks )

Question 26

what is the role of surfactant?

Answer 26

reduces Surface Tension as a result of Fluid in Lungs, preventing Alveolar Collapse

Question 27

what are the 3 routes of aspiration of amniotic fluid?

Answer 27

• vaginal wall increases pressure on fetus 🡪 so it’s forced out by nose and mouth of fetus
• Moves into pulmonary circulation
• Moves into pulmonary lymphatics

Question 28

what is required to close so that breathing can occur?

Answer 28

closing of cardiovascular shunts, which also allows to separate circulatory systems -pulmonary circulation and systemic circulation

Question 29

what can cause respiratory distress syndrome?

Answer 29

insufficient surfactant or insufficient numbers of alveoli

Question 30

precursors of macrophages are called:

A-T cells
B-killer cells
C-B cells
D-plasma cells 
E-monocytes

Answer 30

E

Question 31

during which stage of lung maturation do type 2 pneumocytes form to secrete surfactant?

A-pseudoglandular stage
B-canalicular stage
C-terminal sac
D-alveolar

Answer 31

C