Lecture 8 - Development of the lungs

Question 1

What happens at week 4 of the embryo?

Answer 1

yolk sac visible
somites visible
cns developing
gut tube: foregut, midgut, hindgut
Respiratory diverticulum (lung bud) appears int he ventral wall of the foregut

Question 2

What appears on day 22

Answer 2

a tracheoesophageal ridge develops
grows ventrocaudally
it separates the respiratory diverticulum from the foregut
dorsally is the oesophagus
ventrally - trachea and lung bud now divided to form 2 lung buds

Question 3

What is a tracheoesophageal fistula

Answer 3

abnormal communication
results in incomplete division of foregut into oesophageal and respiratory portions.
in 85-90% of cases - oesophageal atresia (closed or absent)

Question 4

what is oesophageal atresia

Answer 4

lower oesophagus ends abruptly and forms a fistula with the trachea
abdomen distends as stomach fills with air

Question 5

What is a H type tracheoesophageal fistula

Answer 5

approx 4% of cases

milk can be driven into respiratory system as there is an opening from the top and bottom into the trachea

Question 6

What are the other congenital abnormalities associated with TOF’s

Answer 6

VACTERL
Vertebral defects
Anal atresia
Cardiac defects
TOF's
Esophageal atresias
Renal abnormalities
Limb defects

Question 7

Describe the formation of the lungs

Answer 7

partitioning of the oesophagus occurs and respiratory diverticulum forms left and right lung buds
During week 5 - growth and differentiation into main bronchi from secondary bronchi
week 6- further branches results in formation of tertiary bronchi - will each supply a bronchopulmonary sgement (10 on the right and 8 on the left_

Question 8

What happens by week 16

Answer 8

forms terminal bronchioles

Question 9

week 26

Answer 9

respiratory bronchioles

Question 10

week 36

Answer 10

first alveoli

Question 11

How is branching regulated

Answer 11

by interaction of the epithelium with the overlying mesoderm

Question 12

What is derived from the visceral mesoderm?

Answer 12

cartilage, smooth muscle, connective tissue and capillaries

Question 13

Visceral mesoderm forms

Answer 13

visceral pleura

Question 14

parietal mesoderm forms

Answer 14

parietal pleura

Question 15

What is pulmonary agenesis

Answer 15

occurs when lung bud fails to split. absence of bronchi and vasculature. unilateral or bilateral
bilateral - incompatible with life

Question 16

Describe a clinical presentation of pulmonary agenesis

Answer 16

the child usually develops respiratory distress and presents in the first year of life when remaining lung is compromised. usually by lower resp infection
60% have other problems - diaphragmatic hernias, skeletal anomalies,
higher anomalies associated with agenesis of right lung

Question 17

Pulmonary hypoplasia

Answer 17

all components are present but incompletely developed
severity determines extent of compromise
May be found in association with congenital diaphragmatic hernia

Question 18

What are the 4 periods of lung maturation

Answer 18

Pseudoglandular
canalicular
terminal sac
alveolar

Question 19

Pseudoglandular

Answer 19

5-17 weeks
Branching of the respiratory tree has occurred to form terminal bronchioles
respiration not possible - foetus doesn’t survive

Question 20

Canalicular

Answer 20

16-25 weeks
terminal bronchioles give rise to respiratory bronchioles - give rise to alveolar ducts
mesodermal tissue becomes highly vascularised

Question 21

Is respiration possible in the canalicular phase?

Answer 21

possible towards end of this period as some terminal sacs have developed at the end of the respiratory bronchioles and are highly vascularised

Question 22

Terminal sac period

Answer 22

26 - birth 
further terminal sacs
Primitive alveoli develop
epithelium thins and capillaries come into contact with epithelium.
Blood air barrier form
type 1 and type 2 pneumocytes form
surfactant forms a film over the internal walls of terminal sacs
decreases surface tension

Question 23

What will happen to a premature (24 week) baby

Answer 23

can survive if given intensive care but may suffer respiratory disress syndrome

Question 24

Alveolar period

Answer 24

36 to 8 years
development of the lungs after birth is due mainly due to an increase in respiratory bronchioles and alveoli
95% of mature alveoli do not develop until after birth

Question 25

What happens to kick start respiration at birth?

Answer 25

breathing movements start in utero and serve to remove amniotic fluid
Also kick starts muscles of respiration into action
At birth any lung fluid is absorbed by the capillaries
baby’s first breath into lungs - surfactant present in sufficient amounts - respiration possible

Question 26

What happens in respiratory disress syndrome

Answer 26

if child is born prematurely, state of development of lungs is a main factor in determining prognosis.
between 26 weeks and birth - good prognosis as surfactant produced in sufficent quantities.
chances are poor in the canalicular period

Question 27

symptoms of respiratory distress syndrome

Answer 27

eg. birth at 23 weeks
immediate asphyxiation (lack of oxygen)
increased rate of breathing
mechanical ventilation needed to support baby’s breathing
damage to alveolar lining - fluid leaks into alveolus
chronic lung injury could cause bronchopulmonary dysplasia (abnormal formation)

Question 28

Treatments for respiratory distress syndrome

Answer 28

glucocorticoid treatment accelerates fetal lung development and surfactant production

Question 29

What does surfactant therapy involve?

Answer 29

natural or artificial surfactant ( more effective with surfactant A and B proteins)

Question 30

What is surfactant protein B deficiency disease?

Answer 30

genetic condition - autosomal recessive

fatal disease even with surfactant replacement therapy.