Development of the Respiratory System Flashcards
1
Q
What germ layer forms the respiratory system
A
- The endoderm
2
Q
the larynx & trachea are developed in the ___________ of development
A
- 4th week
3
Q
Where does the laryngotracheal groove appear
A
- At the caudal end on the ventral wall of the primitive pharynx
4
Q
Explain the development of the trachea
A
- Endodermal lining of laryngotracheal tube → tracheal & pulmonary epithelium & glands (Wnt2/2b, FGF10, BMP4)
- Splanchnic mesenchyme around the LT tube → cartilage, connective tissue & muscles of the trachea
- LT groove → LT diverticulum → LT tube
- Tracheoesophageal septum separates the LT tube from the pharynx (now esophagus)
5
Q
What does the tracheoesophageal septum do?
A
- It divides the cranial part of the fore gut into the ventral respiratory passageways (NKX2.1,Shh, Wnt7b) and the dorsal digestive passageways (SOX2, BMP7) with BARX1 at the septum
6
Q
Explain the development of the bronchi
A
- A respiratory bud appears at the caudal end of the laryngotracheal diverticulum in the 4th week of development
- The bud divides = 2 primary bronchial buds which then grow laterally → L&R primary bronchi → 2L&3R secondary bronchi → 8-9L&10R tertiary bronchi = 24 orders of branching
- developing bronchi & lungs grow laterally into the intraembryonic coelom = pleural cavity (houses the lungs)
7
Q
What are the 4 stages of lung development
A
- Pseudoglandular stage
- Canalicular stage
- Terminal sac stage
- Alveolar stage
8
Q
What happens in the pseudoglandular stage
A
- “The stage p.t. a false gland” (looks like an exocrine gland)
- This is between weeks 5-17
- Respiration does not take place (bcos alveoli haven’t been developed)
9
Q
What happens in the canalicular stage
A
- This overlaps the pseudoglandular stage (weeks 16-26) bcos its a cranial → caudal development
- the lumina of the bronchi & bronchioles increase
- 24 weeks: terminal bronchioles → respiratory bronchioles, alveolar ducts & terminal sacs
- lung tissue becomes vascular, respiration may be possible
10
Q
What happens in the terminal sac stage
A
- From 26 weeks to birth
- Terminal sacs develop at the end of the alveolar ducts which capillaries bulging into then = alveoli
2 types of alveolar cells - Type I = squamous shaped
- Type II produce pulmonary proteins & fats which decrease surface tension (collapsing alveoli)
11
Q
What happens in the alveolar stage
A
- from 32 weeks to 8 years
- Alveocapillary membrane thins bcos capillaries bulge more into the terminal sacs
- 95% of alveoli form postnatally
- fetus practices breathing in the uterus
12
Q
Explain the developent of the diaphragm
A
- The diaphragm separates the thoracic & abdominal cavities
develops from 4 sources - septum transversum (central tendon of diaphragm)
- pleuroperitoneal membranes (become a smaller component)
- dorsal mesentery of the esophagus
- lateral body walls → peripheral part of the diaphragm
13
Q
What is congenital diaphragmatic hernia
A
- It results from failure of the pleuroperitoneal membranes fusing with the other components of the diaphragm (usually on the left)
- Causes the abdominal organs to enter the thoracic cavity = defective heart & lung development
14
Q
Explain the development of the larynx
A
- Larynx develops at the cranial, distal end for the laryngotracheal tube
- The cartilage of the 4th and 6th pharyngeal arches form the cartilages of the larynx
- Cranial LT tube mesenchyme → arytenoid swellings that grow towards the tongue → glottis
- Laryngeal ventricles from epithelial recanalization in week 10
- Epiglottis formed from hypo pharyngeal eminence
15
Q
What can cause esophageal atresia
A
- Defects in the Shh, Wnt, or BMP pathway or mutations of Sox2 or NKX2.1 (dorsoventral patterning)