Development of the Lungs - Diaphragm and body cavities Flashcards
Body folding to give thoracic cavities
Original coelom will end up as 4 body cavities
1) Pericardial cavity
2) Pleural cavities (2)
3) Abdominal cavity
Origin of the central tendon of the diaphragm
- septum transversum
- starts out at the anterior of the embryo ahead of the developing brain and head
Folding to give the 4 body cavities
- when embryo folds up folds over at 90 degrees to the long axis of the embryo at the head and tail end –> gives head and tail fold
- embryo rolls up in the long axis to give lateral body folds
Where are the fluid filled coeloic cavities after folding
-lie below and on either side of the developing GI trct
Location of prospective pericardial cavity and pleural cavities after folding
Located anterior to the septum transversum (future diaphragm)
Location of future abdominal cavity after folding
-portions that will fuse to form the future abdominal cavity after folding lie behind the septum transversum
Development of the lungs
1) develop as a groove in the floor of the developing digestive tract = laryngotracheal groove
2) Laryngotracheal groove grows down into region between the developing pleural cavities (pleural coeloms) as a lung bud
3) Lung bud branch divides into two buds (left and right bronchial buds)
4) Right then branches into three while left branches into two
5) Lung buds grow sideways out into pleural coeloms and as they grow become invested by the thin sheet of cells lining the coeloms (the splachnic mesoderm) which forms the visceral pleura
6) By week 7 have branched again to form segmental bronchi
7) Lungs continue to grow outwards into pleural cavities (pleural coeloms) and fill all of the space except for that which is occupied by the heart
8) Folds of the membrane divide the pleural colelom off from the pericardial coelom -giving 2 pleural cavities and a pericardial cavity (i.e. parietal pleura?)
Four periods of development lung histology
1) Pseudoglandular 8-16 weeks
- histological structure resembles a gland
- development of pulmonary arteries during this period
2) Canalicular 17-26 weeks
- formation of respiratory bronchi and intense growth of pulmonary blood vessels
3) terminal sacs 26 weeks to birth
- blood-air barier established (type I aveolcyte responsible for gas exchange while type II responsible for surfactant production)
4) Formation of alveoli 32 weeks to 2 years
- also full microvascular maturation by age 2-5 (from double capillary network to single)
- growth of terminal sacules, alveolar ducts and alveoli
Requirements for lung development (3)
1) Adequate thoracic space
2) Foetal breathing movements
3) Adequate amnionic fluid volume
Division of lungs by 24 weeks + what this means for respiration
- as lungs grow out into pleural cavities continue to divide so that by 24 weeks there are 17 orders of branching
- at this point there is still not enough alveolar developmet for respiration (so prognosis of foetus delivered at this point is poor but can maintain life?)
Most important factor in lung development for maintenance of life
- development of type II alveolocyte and its production of surfactant
- surfactanct acts like a detergent - reduces surface tension in the lungs and allows alveoli to open up (otherwise walls of the alveoli will remain stuck together held together by surface tension)
Timeline development of the capillaries
- marginal development at 23 weeks
- adequate development by weeks 24-26
Function of amniotic fluid -respiration
- surrounds the foetus
- foetus breathes the amniotic to help expand the lungs and strengthen the respiratory muscles
Origin of amniotic fluid
- secreted by foetal kidneys
- that which is swallowed by the foetus is reabsorbed into foetal circulation –> maternal circulation
Consequence of inadequate amniotic fluid development (oligohydramnios)
The lungs may be underdeveloped (hypoplastic)
