Systems development V: Lung development Flashcards
How is lung development different to development of most other systems in the body?
It is much later to develop and continues to develop after brith
What four organs are commonly hampered by a baby being born early?
Lungs, brain, digestive system and immune system
What are the 5 stages of lung development?
Embryonic- lasts up until about 8 weeks
Pseudoglandular- runs from 5-16weeks
Canalicular- runs from 16w up until the late second trimester 24/26w
Saccular- runs from 24w till birth
Alveolar- starts just before birth and goes for a 1/2 years after that
Where do main lung structures develop?
During embryonic stage and includes development od primary lung subsections- primary bronchi
How many primary bronchi are there on right and left side?
3 on right and 2 on left due to heart on left
Where does most of the knowledge of regulation of lung development derived from?
Animal studies
How long after birth does lung development continue after birth in humans?
3 years
What is the embryonic stage in lung development?
There is a simple outgrowth of tissue from the digestive system in week 3 and the tissue is a mixture of mesoderm and endoderm. By week 4, the tracheal bud can be identified as separate from the oesophagus. The trachoesophageal septum has formed.
By the end of week 4, primary bronchial buds begin to form and the oesophagus is clearly separate from laryngotracheal tube.
What happens in the pseudoglandular phase ?
Over the next few weeks the lobes of the lung begin to develop
The lung buds grow out of the primary bronchi
Gradually these lung buds brach out, become more convoluted and expand in size
By week 6, you can see 3 lung buds on right sides and 2 on the left which gradually grow over the next couple of weeks to form the lobes of the lung
By the end of the 8 weeks, you have a structure with some glandular features
Between 6-16 wks, there’s not much change in cellular structure which comprises of terminal bronchioles surrounded by connective tissue cells which have lots of capillaries running through them
What happens in the canalicular phase?
There are developing canal like structures and expanding in size, it’s beginning to branch out more
The terminal bronchioles begin to grow outwards into connective tissue in which they’re embedded. They continue to increase in size and complexity
This goes on for another 10 weeks. Therefore both structure and function are changing slowly at this stage
What happens in the saccular phase?
Sacs develop and outgrowth continues
Sacs are single layers of thin squamous epithelial cells. As these terminal cells expand, they start to come into contact with the capillaries. This leads to formation of tight connections between the two structures
What happens in the alveolar phase?
Increased division forming more definitive alveoli. The intimate contact between sacs and capillaries is developing. The interaction is secure with 2 cells perfectly adjacent to each other. Contact between alveoli an lymphatic system. Final structure of the lung is beginning to transpire by this stage.
What are the alveoli like in a mature lung?
They are small, surrounded by cells
There are gaps between the alveoli and the alveoli are interconnected with each other
What are the 2 types of cells in the walls of the alveoli?
Type 1 cell- makes the wall of the alveoli
Type 2 cell- crucial role in secreting surfactant, the material which gives lungs the unique property of not collapsing when we breathing out
What does surfactant allow?
The lungs to remain patent and open during breathing cycle
