Lecture 8 - Development of the lungs Flashcards Preview

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What happens at week 4 of the embryo?

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


What appears on day 22

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


What is a tracheoesophageal fistula

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


what is oesophageal atresia

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


What is a H type tracheoesophageal fistula

approx 4% of cases
milk can be driven into respiratory system as there is an opening from the top and bottom into the trachea


What are the other congenital abnormalities associated with TOF's

Vertebral defects
Anal atresia
Cardiac defects
Esophageal atresias
Renal abnormalities
Limb defects


Describe the formation of the lungs

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_


What happens by week 16

forms terminal bronchioles


week 26

respiratory bronchioles


week 36

first alveoli


How is branching regulated

by interaction of the epithelium with the overlying mesoderm


What is derived from the visceral mesoderm?

cartilage, smooth muscle, connective tissue and capillaries


Visceral mesoderm forms

visceral pleura


parietal mesoderm forms

parietal pleura


What is pulmonary agenesis

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


Describe a clinical presentation of pulmonary agenesis

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


Pulmonary hypoplasia

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


What are the 4 periods of lung maturation

terminal sac



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



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


Is respiration possible in the canalicular phase?

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


Terminal sac period

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


What will happen to a premature (24 week) baby

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


Alveolar period

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


What happens to kick start respiration at birth?

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


What happens in respiratory disress syndrome

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


symptoms of respiratory distress syndrome

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)


Treatments for respiratory distress syndrome

glucocorticoid treatment accelerates fetal lung development and surfactant production


What does surfactant therapy involve?

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


What is surfactant protein B deficiency disease?

genetic condition - autosomal recessive
fatal disease even with surfactant replacement therapy.