development of the lungs Flashcards
special characteristics of the lungs
late to functional development
only system not to be operational before birth
development respiratory diverticulum
forms at week 4
ventral out pouching of foregut from splanchnopleure
respiratory epithelium derived from splanchnic endoderm
supporting mesenchyme from splanchnic LP mesoderm
starts of the development of the lungs
first bifurcation creates the primary bronchi
stage 1 of the development of the lungs
embryonic stage
- primary bronchial buds branch into secondary bronchi
- secondary bronchi branch and create tertiary bronchi, vasculogenesis also occurs around airway buds
secondary bronchi
called lobular bronchi because they are equal to the number of lobes
tertiary bronchi
future bronchopulmonary segments
stage 2 of development of the lungs
pseudo glandular phase
final number of bronchopulmonary segments are fromd
terminal bronchiole branches develop from tertiary bronchi
still has thick wall and dense mesenchyme
stage 3
canalicular phase (w28-36) terminal bronchioles bud into respiratory bronchioles, alveolar ducts and primitive alveoli walls thin and epithelium begins to differentiate
stage 4
saccular stage
develop alveolar sacs - primitive alveoli
type 1 and 2 pneumocystis develop
surfactant begins being produced in a greater quantity and quality
stage 5
alveolar stage
alveolarisation - septation and multiplication of alveoli
primitive alveoli continue to differentiate into definitive alveoli
further thinning of airspace walls
form and differentiate in craniocaudal fashion
stage 5 divided into
two stages
63w - 2/3 years - first phase of alveolarisation
2/3 years - 18/22 years - second phase of alveolarisaton
until 18-22 years: enlargement of terminal bronchioles and alveoli
first stage 5
fast
second tage 5
slow
enlargement of terminal bronchiole and alveoli
stage 6 - microvascular maturation
birth - 3-21 years
time Fram remains uncertain
fusion of aveolar capillary networks
septum transversum
becomes the central tendon of the diaphragm
foremost mesenchymal tissue of the embryonic disk, cranial to the cardioogenc centre
movement of the septum transverse
originally cranial to the cariogenic centre
cranial part of head tail folding drags it in front of the yolk sac
arrests caudally to the heart
what becomes the central tendon of the diaphragm
septum transversum
where does the diaphragm muscle develop
under the tongue C3-5
migrate ventrally and caudally, through the lateral aspect of body wall
within the developing pleuropericardial folds
developing lung buds
push on coelomic space dorsal to the phrenic nerve
the body wall grows outward faster so the pleural space is always going to be larger
tracheoosophageal fistula
when the oesophagus doesn’t directly connect to the stomach
connected to the trachea
with or without concurrent atresia of trachea/oesophagus
congenital diaphragmatic hernia
incomplete fusion of septum transversum and pleuroperitoneal fold
50% mortality rate
part of the colon comes up through the unfused pleuroperitoneal canal
asymmetric branching abnormalities
unilateral agenesis - no development of a lung
aplasia - bronchi but no lung tissue (almost a lung)
hypoplasia - some lung tissue but no alveoli, just conductive tubes
unilateral agenesis
missing lung - trachea not bifurcated
branching abnormality - aplasia
bronchi but no lung tissue
branching abnormality - hypoplasia
some lung tissue but no alveoli
surfactant production
only starts 24-34 weeks - variable
holds smaller airways open by reducing surface tension of the fluid around the alveoli
results in equalised air flow to variably sized air sacs
needs to be constantly produced in high quantity and quality
lack of surfactant
cannot retain air once inflated = respiratory distress syndrome
damage and developmental impairment and mortality
low survival
purpose of surfactant
x10 drop in surface tension
respiratory distress syndrome
lack of surfactant at birth
considerations for pre term birth
- surfactant to be produced
- lungs need to have minimal diffusion distance
- diaphragm needs to be able to do the work of breathing
- thorax needs to be rigid enough to resist the diaphragm
when is surfactant produced enough
usually 28 weeks
when does the saccular stage happen
28-36 weeks
term is 38 weeks
therefore primitive alveoli are still forming 2 weeks before birth
surfactant may not be being formed enough in time for birth if premature
movement of septum transversum
originally cranial to the cariogenic centre
head part of head tav folding drags t is from of the heart
arrests at the underside of the heals
what do the pleuralpericardall folds do
petition the chest into 3 cavities
means that the other side can function even if one is collapsed
plueropericardal and plueroperitoneal folds
plueropericardal fold s the fold created by the phrenic nerve
pluertoperitoneal fold is the space occluded by the pleuropericardial fold
pericardioperitoneal canals are closed by
plueroperitoneal fold to form pleuroperitoneal membrane
muscular ingrowth from the body wall
forms part of the diaphragm
oesophageal mesentery forms
crura of the diaphragm
pre term birth implication of compliance
preterm babies have not sufficiently red ribs
when the diaphragm moves, the walls collapse with the diaphragm and volume/pressure isn’t changed
