The First Breath Flashcards
Stage of lung development
Embryonic 0-5 weeks
Pseudoglandular 5-17 weeks
Cannalicular 16-25 weeks
Alveolar 25 weeks-term
Lung development
Lungs come from foregut derivative- anterior outpouching From an oesophageal appendix
By the 5th week the lung buds enlarge to form right and left main bronchi
Pseudoglandular phase
5-17 weeks
Exocrine gland only
Major structural units formed.
Angiogenesis- the formation of new blood vessels
Mucous Glands
Cartilage
Smooth Muscle
Cilia
Lung fluid
At this stage the lungs aren’t being used to oxygenate the embryo but instead then mother’s oxygen supply via the umbilical artery and vein
Canalicular phase
16-25 weeks.
Distal Architecture
Vascularisation i.e formation of capillary bed
Respiratory bronchioles.
Alveolar ducts.
Produces Terminal sacs
Alevolaristaion
25 weeks until birth
Alveolar sacs
Type 1 and Type 2 cells
Alveoli simple with thick interstitium
Birth to 3-5 years
Thinning of alveolar membrane and interstitium
↑ complexity of alveoli
Slide 12
Things that go wrong
Embryonic phase
Pseudoglandular phase
Alveolar phase
Physiology- systemic blood vessels (non pulmonary vessels such as aorta)
Purpose: deliver oxygen to hypoxic tissues
Hypoxia/acidosis/CO2 is vasodilator
Oxygen is vasoconstrictor
(Opposite to what happens in the pulmonary vessels as here hypoxia is a vasoconstrictor )
Physiology- Pulmonary blood vessels
Purpose: pick up oxygen from oxygenated lung
Oxygen is vasodilator
Hypoxia/acidosis is vasoconstrictor
If you had a hypoxic part of the lung you wouldn’t want to send blood to it, rather send it to area where oxygen can be collected faster, but if you have a hypoxic part of finger, vessels dilate to send oxygen to this part of finger faster
Foetal circulation
Lung is not useful organ to fetus
PaO2 = 3.2 kPa (31,000 feet)
Shunting of blood Right to Left
-High Pulmonary vascular Resistance (hypoxia leads to vessels constricting)
-Tissue resistance (fluid filled)
-Low systemic resistance (placenta)
Right blood flow goes straight into the systemic
Lung fluid
Fetal airways are distended with fluid
Fluid aids in lung development
Actively secreted by lungs- alveoli are actively filled with fluid to prepare them for the first breath
Circulation and breathing in foetus before first breath
when blood comes into the right atrium, then the
right ventricle into the pulmonary artery, it goes straight into the aorta because there’s no point in going into the
lungs
The lungs are fluid filled and they do not carry out any useful function in the foetus.
So this is one method by which there is a right to left shunt and the foremen oval allows this- so there is 3 shunts present in foetus but this all changes rapidly as soon as first breath is taken as at this point lungs becomes active and fill with blood. Left shunting also immediately stops at this point
Adaptive changes at birth
Fluid squeezed out of lungs by birth process. Cough reflex is activated by the fluid that has been squeezed out of the alveoli
Adrenaline stress leads to increased surfactant release.
Air inhaled
Oxygen vasodilates pulmonary arteries so pressure in the right side drops down
Umbilical arteries constrict
Ductus arteriosus constricts
Ductus arteriosus: pulmonary trunk linked to the distal arch of aorta by the ductus arteriosus, permitting blood to bypass pulmonary circulation
Laplaces law
Smaller alveoli may preferentially shut whilst larger alveoli may preferentially open at a given surface tension so surface tension keeps smaller alveoli open in balance of the adhesive and surfactant forces
What is the role of surfactant?
Virtual abolition of surface tension- keep the alveoli from shutting due to balance between cohesive and adhesive forces
Allows homogenous aeration and allows maintenance of functional residual capacity
Surfactant deficiency
The alveoli will prematurely collapse
Develop:
Respiratory distress syndrome
Loss of lung volume
Non-complaint lungs
Uneven aeration
Caused by
Prematurity
Asphyxia
Cold
Stress
Twins
Increased by
Distension of alveoli
Steriods
Adrenaline
