19. Development of the respiratory system

Question 1

Stages:

Answer 1

1. Embryonic
2. Pseudoglandular stage
3. Canalicular stage
4. Saccular stage
5. Alveolar stage

mnemonic: End Poker Cause Sadi Arrived

Question 2

embryonic stage : weeks 4-7

Answer 2

Formation of the Laryngotracheal Diverticulum: around the 4th week of gestation,
from the ventral wall of the foregut, the laryngo tracheal diverticulum forms. Later on it will elongate and birfucate into primary bronchi buds

Development of the Tracheoesophageal Septum: the tracheoesophageal septum separates the trachea from the esophagus.

–which will form the right and left bronchi.

Question 3

Pseudoglandular Stage (Weeks 5-17)

Answer 3

Branching Morphogenesis:

from primary bronchial buds to whole bronchial tree up to terminal bronchioles form
but there are no repsiratory bronchioles or alveoli present yet

Question 4

Canalicular Stage (Weeks 16-26)

Answer 4

Formation of Respiratory Bronchioles:

-Terminal bronchioles divide into respiratory bronchioles and alveolar ducts.

-Vascularization increases, and the capillary network develops around the airways, crucial for future gas exchange.

Question 5

Saccular Stage (Weeks 24-38)

Answer 5

from respiratory bronchioles to the formation of terminal sacs -primitive alveoli

-Type I and Type II alveolar cells differentiate.*

-Type II alveolar cells begin to produce surfactant, a substance that reduces surface tension within the alveoli and is essential for lung function after birth.

Question 6

Alveolar Stage (Late Fetal Period to Childhood)

Answer 6

Maturation of Alveoli:

-Terminal sacs continue to develop and mature into alveoli.

-Alveoli continue to increase in number and mature structurally and functionally after birth, particularly until around 8 years of age.

Question 7

Key Developmental Milestones

Answer 7

Weeks 4-7: Formation of the laryngotracheal diverticulum, trancheoesophageal septum: trachea from eosophagus , and primary bronchi.

Weeks 5-17: Formation of the bronchial tree up to terminal bronchioles.

Weeks 16-26: Development of respiratory bronchioles and initial formation of terminal sacs.

Weeks 24-38: Continued development and initial functional maturation of terminal sacs.

Birth to 8 years: Postnatal alveolar development and maturation.