Development of lungs Flashcards
Start of respiratory development
Respiratory primordium develops as a ventral groove in the floor of the foregut (originally from the gut tube)
Foregut
Region from mouth to pancreas
Respiratory primordium
Gives rise to the trachea, larynx, lungs
General development steps of respiratory system
- Respiratory primordium develops as a ventral groove in floor of foregut
- Groove deepens and forms elongated outgrowth called laryngo-tracheal groove
- The laryngo-tracheal groove becomes separated from the foregut by two trachea-oesophageal grooves (one on each side). These two grooves move towards each other and fuse to form the trachea-oesophageal septum and form the laryngo-tracheal tube. The portion of the foregut that was cut off from this will become the pharynx
- Laryngo-tracheal tube becomes the primitive trachea and eventually splits into two bronchial buds
- Primitive trachea- mesenchyme (neural crest derived) gives rise to cartilaginous tracheal rings and smooth muscle of the trachea. Endodermal lining becomes ciliated, pseudostratified respiratory epithelium with goblet cells. - Lung buds grow caudo-laterally becoming principle bronchi (left bud will be more lateral; right more caudal).
- Principle bronchi bud into lobar bronchi.
- Lobar bronchi will push into developing pleural cavity, become surrounded by mesenchyme and form the pleura
- Lobar bronchi will bud into segmental bronchi
- Segmental bronchi divide up to 20 times (species dependent) into terminal bronchioles (which are lined with endodermal derived epithelium)
- Terminal bronchioles divide further into respiratory bronchioles
- More divisions create secondary tubules called canalicules or alveolar ducts
- Canaliculi form terminal saccules. These divide further into blind saccules that will differentiate into alveoli (saccular phase) OR the alveoli differentiation will occur first on the terminal saccules (alveolar phase).
- Primitive alveoli that allow newborn to breath initially are developed into mature alveoli
Primitive trachea
- Endodermally lined. Becomes ciliated, pseudostratified respiratory epithelium with goblet cells
- Mesenchyme around it is neural crest derived and gives rise to cartilaginous tracheal rings and smooth muscle of trachea.
Periods of bronchi and lungs development
- Embryonic- primordium of lungs and bronchi formed
- Fetal- ramified bronchi are formed and preliminary structures produced for gas exchange
- Postnatal- definitive structures for gas exchange called alveoli develop and lungs take on their adult form. Marked by extensive growth of respiratory bronchioles, accules and alveolar development.
Fetal period development subdivisions
Pseudo-glandular
- Segmental bronchi divide lots into terminal bronchioles
Canalicular
- Terminal bronchioles divide into respiratory bronchioles. Further divisions create secondary tubules called canalicules or alveolar ducts
Saccular
- Terminal saccules divide further into blind saccules that will differentiate into alveoli
Alveolar
- alveoli differentiation will occur first on the terminal saccules
Tracheal bronchus
develops from the trachea to supply right cranial lobe in cattle, sheep, and pigs
Pleural cavity development
- heart and lungs will originally be surrounded by left and right segments of pleuro-pericardial cavity
- Pleuro-pericardial folds (folds of mesoderm) will grow medially into the left and right parts of the pleuro-pericardial cavity and will eventually fuse to separate the two cavities
- heart will be suspended in one pericardial cavity. Lungs will be in the pleural cavity
What lines terminal bronchioles?
Lined with endodermal derived epithelium
Lungs during gestation
Lungs were filled with fluid secreted from developing alveolar cells and glands in system, and from amniotic fluid that was aspirated by fetus.
Lungs in postnatal period
- Fluid is expelled
- Anything left over is absorbed by epithelial cells
Subdivisions of canine lungs
Linked by lobar branches
Left
- Cranial lobe (has a cranial Lobe and a caudal lobe)
- Caudal lobe
Right
- Cranial lobe
- Middle lobe
- Accessory lobe
- Caudal lobe
Subdivisions of porcine lungs
Linked by lobar bronchi except the right cranial lobe
Left
o Cranial lobe (has a cranial Lobe and a caudal lobe)
o Caudal lobe
Right
o Cranial lobe- Linked by tracheal bronchus
o Middle lobe
o Accessory lobe
o Caudal lobe
Subdivisions of ovine lungs
Left
- Cranial lobe (has a cranial part and a caudal part)
- Caudal lobe
Right
- Cranial lobe (has a cranial and caudal part)- Linked by tracheal bronchus
- Middle lobe
- Accessory lobe
- Caudal lobe