First breath Flashcards
stages of lung development
Embryonic 0 - 5 weeks
Pseudoglandular 5 - 17 weeks
Cannalicular 16 - 25 weeks
Alveolar 25 weeks – term
Describe the embryonic stage of lung development
0-5 weeks
lung bud develops form the foregut and splits into 2 (later go on to form left and right lung)
tube pinches off from forgut to form early trachea and eosophagus
Describe the pseudoglandular stage of lung development?
5 - 17 weeks
Major airways defined- early bronchiole tree formed
Nests of angiogenesis (blood vessel formation)
Smaller airways down to respiratory bronchioles
epithelial cell differentiation
Describe the cannalicular stage of lung development?
16-25 weeks
.
respiratory bronchioles
Capillary Beds
Alveolar ducts
Describe the saccular/alveolar stage of lung development?
25 weeks to birth
Alveolar budding, thinning and complexification
Birth to 3-5 years roughly continued development:
Thinning of alveolar membrane and interstitium
↑ complexity of alveoli
Things that can go wrong:
Embryonic 0 - 5 weeks
Laryngeal, tracheal and oesophageal atresia, tracheoesophageal fistula, tracheal and bronchial stenosis, pulmonary agenesis
Pseudoglandular 5 - 17 weeks
Bronchopulmonary sequestration, cystic adenomatoid malformations, alveolar-capillary dysplasia
Alveolar 25 weeks – term
Acinar dysplasia, alveolar capillary dysplasia, pulmonary hypoplasia, respiratory disease of the newborn
How are lungs bypassed in feotal circulation?
lungs are non-functioning: blood is shunted right to left
High pulmonary vascular resistance (due to hypoxia causing vasoconstriction)
High tissue resistance
Foetal airways are distended with fluid
Low systemic resitance
Describe feotal circulation including the use of shunts
Oxygen and nutrients from the mother’s blood pass through the umbilical cord to the fetus. The blood from the umbilical cord goes to the liver, where some (30%) of it goes through the ductus venosus shunt bypassing the liver and staright to vena cava.
Most of the oxygenated blood goes to the inferior vena cava, then into right atrium. Most of the blood flows through the foramen ovale and into left atria and then left ventricle. It then leaves heart to supply body by aorta. Any blood that did move into right atria is shunted back into aorta by ductus arteriosus which joins pulmonary trunk to aortic arch.
What is the ductus arteriosis?
Pulmonary trunk linked to the distal arch of aorta by the ductus arteriosus, permitting blood to bypass pulmonary circulation
direction of umbilical vein vs artery
umbilical vein- away from placenta towards heart
umbilical artery- towards placenta away from heart
How does ductus arteriosis shut?
The muscular wall contracts to close after birth (a process mediated by bradykinin)
what is the ductus venosus?
Oxygenated blood entering the foetus also needs to bypass the primitive liver. This is achieved by passage through the ductus venosus, which is estimated to shunt around 30% of umbilical blood directly to the inferior vena cava
(colaspses at birth)
what is the foreamen ovale
The foramen ovale is a passage between the two atria, which is responsible for bypassing the majority of the circulation
(post-birth shuts due to chnages in pressure)
changes to lugs during birth:
Fluid squeezed out of lungs by birth process
Adrenaline stress leads to increased surfactant release by type II
Gas (air normally) inhaled
Oxygen vasodilates pulmonary arteries,
Pulmonary vascular resistance falls,
Right atrial pressure falls, closing foramen ovale
Umbilical arteries constrict
Ductus arteriosus constricts
What is laplace’s law?
P=2T/R (don’t memorise)
pressure= 2xsurface tension / resistance
