First Breath Flashcards
Stages of lung development
Embryonic
Pseudoglandular
Cannalicular
Alveolar
Time period of lung development: embryonic
0-5 weeks
Time period of lung development: pseudoglandular
5-17 weeks
Time period of lung development: cannalicular
16-25 weeks
Time period of lung development: alveolar
25 weeks - term
Embryonic lung development
Foregut derivative - anterior outpouching
An oesophageal appendix
Lung buds
By the 5th week the lung buds enlarge to form right and left main bronchi
Pseudoglandular lung development
Exocrine gland only
Major structural units formed
Angiogenesis
Mucous Glands
Cartilage
Smooth Muscle
Cilia
Lung fluid
Cannalicular lung development
Distal Architecture
Vascularisation; i.e. formation of capillary bed
Respiratory bronchioles
Alveolar ducts
Terminal sacs
Alveolar lung development
Alveolar sacs
Type 1 and Type 2 cells
Alveoli simple with thick interstitium
Birth to 3-5 years lung development
Thinning of alveolar membrane and interstitium
↑ complexity of alveoli
5-17 weeks; what happens
Major airways defined
Nests of angiogenesis
Smaller airways down to respiratory bronchioles
16-25 weeks; what happens
Terminal bronchioles
Capillary beds
Alveolar ducts
25-40 weeks; what happens
Alveolar budding, thinning and complexification
What can go wrong during lung development: embryonic
Laryngeal, tracheal and oesophageal atresia, tracheal and bronchial stenosis, pulmonary agenesis
What can go wrong during lung development: Pseudoglandular
Bronchopulmonary sequestration, cystic adenomatoid malformations, alveolar-capillary dysplasia,
What can go wrong during lung development: alveolar
Acinar dysplasia, alveolar capillary dysplasia, pulmonary hypoplasia, respiratory disease of the newborn
Vasoconstrictor of systemic vessels
Oxygen
Vasodilators of systemic vessels
Hypoxia
Acidosis
CO2
Systemic vessels purpose
Deliver oxygen to hypoxic tissues
Vasodilator of pulmonary vessels
Oxygen
Vasoconstrictor of pulmonary vessels
Hypoxia
Acidosis
CO2
Fetal circulation
PaO2= 3.2KPa
Shunting of blood from right to left
High pulmonary vascular resistance (hypoxia)
Tissue resistance (fluid filled)
Low systemic resistance (placenta)
Fetal airways
Distended with fluid
Fluid aids in lung development
Actively secreted by lungs
Ductus arteriosus
Pulmonary trunk linked to the distal arch of the aorta by the ductus arteriosus, permitting blood to bypass pulmonary circulation
Muscular wall contracts to closed after birth
What is closure of ductus arteriosus mediated by
Bradykinin
Ductus venosus
Oxygenated blood entering the fetus also needs to bypass the primitive liver- achieved by passage through the ductus venosus
What percentage of blood does the ductus venosus shunt from umbilical cord directly to inferior vena cava
30%
Foramen ovale
Passage between 2 atria - responsible for bypassing the majority of the circulation
Pathway of oxygenated blood from maternal supply
Umbilical vein —> bypasses primitive liver (ductus venosus) —> enters inferior vena cava —> right atrium —> (via Foramen ovale) left atrium —> left ventricle —> aorta
If blood enters pulmonary trunk, ductus arteriosus shunts blood to aorta
Immediately after birth: ductus arteriosus
Constricts, allowing all blood leaving the right ventricle to travel to the lungs via the pulmonary arteries
Becomes Ligamentum arteriosum
Immediately after birth: Foramen ovale
Closes, leaving a small depression called the fossa ovalis
This isolates deoxygenated and oxygenated blood within the heart
Immediately after birth: ductus venosus
Degenerates and becomes the Ligamentum venosum
First birth
Fluid squeezed out of lungs by birth process
Adrenaline stress leads to increased surfactant release.
Gas inhaled
Oxygen vasodilates pulmonary arteries
Pulmonary vascular resistance falls
Right atrial pressure falls, closing foramen ovale
Umbilical arteries constrict
Ductus arteriosus constricts
What leads to increased surfactant release at birth
Adrenaline stress
Surfactant - first breath
Surface active phospholipid and surfactant proteins A, B, C, D
Produced by Type II pneumocytes from 34 weeks gestation
Dramatic increase in 2 weeks prior to birth
Laplace’s law
Pulmonary pressure needed to prevent collapse =
(2 x surface tension) / radius
If smaller radius- thicker layer of surfactant required
What produces surfactant
Type II pneumocytes
Function of surfactant
Virtual abolition of surface tension- prevents alveolar collapse and maintains FRC
Allows homogeneous aeration
Allows maintenance of functional residual capacity
Oxygenises bacteria—> phagocytosis
Surfactant deficiency
Prematurity
+ Asphyxia
+ Cold
+ Stress
+ Twins
Respiratory Distress Syndrome
Loss of lung volume
Non-compliant lungs
Uneven aeration
Surfactant increased by
Distension of alveoli
Steroids
Adrenaline
Pulmonary interstitial emphysema (PIE)
Lung cysts
Ruptured alveoli
Management of pulmonary interstitial emphysema
Warmth
Surfactant replacement (if intubated)
Oxygen and fluids
Continuous Positive Airway Pressure (maintain lung volumes, reduce work of breathing)
Positive pressure ventilation if needed
Adaptive changes at birth
Drops R sided pressure and moves to 4 chamber system
First breath initiates adaptation
Oxygen causes pulmonary vasodilation
Tissue resistance reduces
Vasoconstriction of ductus arteriosus and umbilical arteries
Respiratory diverticulum
Outbranch of the foregut
Forms the trachea and lung buds in week 4
Atresia
Failure of trachea and oesophagus to separate
At what age do alveoli stop developing
5
Why are developing lungs full of fluid
Type 2 pneumocytes contain NKCC2:
Cl- active transport to fill developing lungs with fluid
Persistent hypoxia
Ductus arteriosus remains open
How is amniotic fluid removed from lungs when born
Expelled (cough) or absorbed into circulation
Why does Foramen ovale close
LA pressure > RA pressure
Why does ductus arteriosus close
Systemic BP (aorta) > pulmonary BP (pulmonary artery)
Eisenmenger’s syndrome
Ventricular septum defect forms shunt between left and right ventricle
Hypoxaemia as pulmonary circulation bypassed
Leads to cyanosis, clubbing and polycythaemia
Which week of gestation is type 2 pneumocytes produced
34
Prior to birth the lungs contain no air; at birth air is drawn into the lungs. Which statement regarding pulmonary physiology after birth is correct?
Persistent hypoxia will cause the ductus arteriosus to remain open
