Development of Respiratory system - Leah Flashcards
Laryngotracheal Groove and lung form in week _____.
week 4
Laryngotracheal groove appears in the ____________.
Floor of caudal pharynx
The lung bud is formed by what?
By the laryngotracheal groove protrudes ventrally forming an endoderm outgrowth from the foregut.
_______ develops and separates lung bud (ventrally) from the foregut (Distally)
Tracheoesophageal septum
_______ develops and separates lung bud (ventrally) from the foregut (Distally).
Tracheoesophageal septum
The respiratory diverticulum retains a connection with the pharynx at the ______.
Primordial laryngeal inlet.
What causes Esophageal Atresia?
caused by posteriorly deviating septum
What are the derivatives of the Lung Bud? (2)
Endoderm = epithelial lining + glands or airways
Splanchnic mesoderm = smooth muscle + CT of airways.
Describe the Development of the Larynx….
Laryngeal cartilages and musculature arise from pharyngeal arch pairs 4 & 6.
Describe development of epiglottis…
Epiglottis from from mesenchyme of the caudal hypopharyngeal eminence.
Laryngeal mm. arising from 4th arch are innervated by __________.
Superior laryngeal N.
Laryngeal mm. arising from 6th arch are innervated by __________.
recurrent laryngeal N.
What is lung bud splitting and when does it occur?
Lung bud divides to form 2 primary bronchial buds (future primary bronchi)
*Occurs on day 28
What happens on day 30 in regards to lung bud splitting?
Primary bronchial buds divide to from secondary bronchial buds (3 on right, 2 on left)
*Each secondary bud will supply one lobe of the lung.
Secondary bronchial buds divide yet again to form what?
Tertiary (segmental) bronchial buds (10 on right, 8-9 on left)
Tertiary bronchus + surrounding tissue = ?
A bronchopulmonary segment
What is the pathway of respiratory tree branching?
Trachea -> PRimary bronchi -> secondary Bronchi - > tertiary (segmental) bronchi -> bronchioles -> terminal Bronchioles -> respiratory bronchioles -> alveolar ducts -> terminal sacs (primitive alveoi)
What are the 4 stages of lung development?
Pseudoglandular (6-16 weeks)
Canalicular (16-26) weeks
Terminal Sac (26 weeks - birth)
Alveolar (32 weeks to 8 years of age)
What happen during the Pseudoglandular stage?
Lung tissue appears histologically as a collection of exocrine glands
All major lung structures have developed except for most distal portions of respiratory tree where gas exchange occurs (respiratory bronchioles + alveolar sacs)
What happen during the Pseudoglandular stage?
Lung tissue appears histologically as a collection of exocrine glands
All major lung structures have developed except for most distal portions of respiratory tree where gas exchange occurs (respiratory bronchioles + alveolar sacs)
* A fetus born here will not survive!
What happens during the Canalicular stage?
Lung tissue becomes highly vascular.
At end of this stage, respiration is possible. Each terminal bronchiole has split into 2 (+) respiratory bronchioles which have developed primitive alveolar ducts. Some ducts already lead into terminal sacs.
*Fetus may survive if born at this stage, but many die as lungs are still immature in their development.
What happens at Terminal Sac Stage?
More terminal sacs develop and are hugged by capillaries establishing the BLOOD AIR BARRIER.
At week 26: terminal sac walls = a single layer of simple squamous cells, most of which are Type I alveolar cells through which gases diffuse.
Scattered amongst the Type I cells are a few rounded Type II alveolar cells: produce, store, and secrete pulmonary surfactant.
