Lecture 8 - Development of the lungs Flashcards
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
VACTERL Vertebral defects Anal atresia Cardiac defects TOF's 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
Pseudoglandular
canalicular
terminal sac
alveolar
Pseudoglandular
5-17 weeks
Branching of the respiratory tree has occurred to form terminal bronchioles
respiration not possible - foetus doesn’t survive
Canalicular
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.
