Embroyology And Lung Growth Flashcards
Week 4 (lungs)
▪️formation of laryngotracheal groove from caudal end of primordial pharynx
-gives rise to trachea, bronchi and bronchi tree
▪️end of week four formation of laryngotracheal diverticulum which elongated to form respiratory bud.
Tracheoesophageal fistulas
▪️abnormal connection between trachea and oesophagus
-upper oesophagus closed off, lower oesophagus attached to trachea (90%)
-both upper and lower are closed of.
▪️failure of tracheoesophageal septum to divide
-reflux of saliva and milk
-reflux of acid into lungs
-excess accumulation of amniotic fluid
Week 5 (lungs)
▪️lung buds grow laterally into pericardio-peritoneal canals (pleural cavities)
▪️secondary and tertiary bronchial buds develop
▪️differentiation of buds into bronchi
▪️enlargement of bronchial buds to form main bronchi
Pseudoglandular phase of lung development
▪️5-16 weeks
- developing lungs resemble exocrine glands
- tubes lined with cuboidal epithelia cells
- by 16 weeks all major elements have formed except those in gas exchange
Canalicular phase of lung development
▪️16-26 weeks
- overlaps with pseudoglandular stage as cranial segments of the lungs develop faster than caudal
- lumen of bronchi and terminal bronchioles become larger
- lung tissue becomes highly vascularised
- end of 24 weeks bronchioles give rise to 2 or more respiratory bronchioles- divides 3-6 times to form primordial alveolar ducts
Terminal sac phase of lung development
▪️26 weeks-birth
- more terminal sacs develop with thin endothelium
- capillary network bulge into developing alveoli
- gas exchange can now take place if fetus is born at 26+ weeks
- production of lung surfactant
The pleura development
▪️visceral pleura
-as lungs developed they acquire layer of VP from splanchnic mesenchyme
▪️parietal pleura
-thoracic wall becomes lined by a layer of PP derived from somatic mesoderm
▪️lungs and pleural grow caudally
Lung surfactant
-starts 20 weeks
▪️released by rounded secretory epithelial cells (type II pneumocytes)- surrounded by squamous epithelial cells
▪️mixture of phospholipids and proteins
▪️forms a mono molecular filmover internal walls of alveolar sacs
-decreases surface tension forces
-helps with stretch of alveoli to prevent collapse during exhalation (atelectasis)
▪️adequate levels reached by 26-28weeks
▪️production increased hugely during last 2weeks of pregnancy
-antenatal corticosteroids induce surfactant production
Respiratory distress syndrome
▪️developmental insufficiency of surfactant production
▪️decreases with gestational age
-50% of babies born at 26-28 weeks
-25% of babies born at 30-31 weeks
▪️blue-coloured lips, fingers and toes
▪️rapid shallow breathing
▪️requires ventilator and treatment with artificial surfactant
Alveolar phase of lung development
▪️32 weeks- 8 years
-epithelial lining becomes thin, squamous epithelial layer (type I pneumocytes)
-adjacent capillaries bulge into alveolar sacs
▪️capable of respiration as alveoli capillary membrane is thin enough to allow gas exchange
Respiratory changes at birth
▪️transition from dependant on placenta to autonomous gas exchange depends on :
- production of surfactant
- transformation of lungs from secretory to gas exchange organs
- formation of pulmonary and systemic circulation
Transition neonatal changes
▪️circulation of fetal blood through placenta ceases and neonatal lungs expands and begin to function
▪️blood flow increases to the pulmonary circulation
▪️3 shunts start to close and are no longer needed
-Ductus venosus- allowed oxygenated blood to bypass liver
-foramen ovale- hole in heat between atrias
-ductus arteriosus- allows blood to by pass lungs
Newborn vs adult alveolar
▪️95% of mature alveoli develop postnatal
▪️newborn -150mil primordial alveoli- denser
▪️adult - 300mil alveoli (between 3and8)
