pre and post natal development of RS

Question 1

Nasal placodes:

Answer 1

-Bilateral thickening of the ectoderm
-develop by the end of the 4th week at the inferolateral parts of frontal nasal prominence

-mesenchyme in their margins produce medial and lateral nasal prominences, which proliferate and form nasal pits

which are the primordials of nostrils and nasal cavities.

Question 2

development of paranasal sinuses;

Answer 2

-they develop after birth, except maxillary sinuses, develop late in fetal life from diverticula of nasal cavity walls.

AIR FILLED

Question 2

Nasal concha develop:

Answer 2

-they develop as elevations in the lateral walls of nasal cavities
-olfactory epithelium is formed

Question 2

Nasal sacs:

Answer 2

• are intially separated from oral cavity by the oronasal membrane.
  -this membrane ruptures by the end of the 6th week of development, connecting the** oral** and nasal cavities

NOT pharynx

Question 3

Lower respiratory organs:

Answer 3

-develop during the 4th week
- primodium of lower resp tract (starts development here) is the laryngotracheal groove. (on the 4th level of pharyngeal pouches).

-endoderm lining gives rise to **epithelium and glands **

-splanchnic mesoderm gives rise to** connective tissue, cartialage, and smooth muscle.**

Question 4

Larynx development:

epithelium, cartialages, mesenchyme

Answer 4

-epithelium develops from endoderm of cranial end of laryngotracheal tube.

-cartialages develop from cartialages in th 4th and 6th pairs of pharyngeal arches.

-mesenchyme dervied from neural crest cells

Question 4

Laryngotracheal diverticulum:

Answer 4

• forms by the end of the 4th week
  -located ventral to the caudal part of foregut
  -forms the globular respiratory bud
  -separates from primordial pharynx

Question 5

larynx development:

epiglottis, trachea

Answer 5

-epiglottis develops from caudal part of hypopharyngeal eminence.
- which is produced from mesenchyme in ventral ends of 3rd and 4th pharyngeal arches

-growth of larynx and epiglottis is rapid during the first three years after birth

-trachea develops in laryngotracheal tube distal to larynx

Question 5

development of respiratory bud:

Answer 5

-divides into 2 bronchial buds
-which enlarge to form main bronchus early in 5th week
-then subdivides into secondary bronchi

-right inferior secondary bronchus divides into 2 bronchi to middle and lower lobes of right lung

Question 6

segmental bronchi and respiratory bronchioles form on the:

Answer 6

-segmental bronchi form on the 7th week

-respiratory bronchioles form at the 24th week

Question 6

splanchinic mesoderm gives rise to:

somatic mesoderm gives rise to:

Answer 6

1) cartilinagous plates of bronchi
2) bronchial smooth muscle and connective tissue
3) pulmonary connective tissue
4) capillaries
5) visceral pleura

parietal pleura from somatic mesoderm

Question 7

1)pseudoglandualar period:

Answer 7

-occurs between 6th and 16th week
- lung elements involved with gas exchange not formed
- respiration NOT possible

Question 8

2) Canalicular period

Answer 8

-occurs between 16th and 26th weeks
-lumina of bronchi and terminal bronchioles become larger
-**lung tissue becomes highly vascular **
-respiratory bronchioles are formed

Question 8

3)Terminal sac

Answer 8

-occurs in 26th week
-More terminal sacs develop and capillaries buldge into alveoli
-blood air barrier is established
-alveoli lined by type I and type II alveolar cells

Question 9

4)alveolar stage:

Answer 9

occurs during 32 weeks- 8 years after birth

-**Gas exchange is allowed **
-lung is prepared to function
-95% of alveolar development is here
-alveolar development is largely complete by 3 years of age