Embryology of the Respiratory system

Question 1

The respiratory system

Answer 1

• does not carry out its physiological function until after birth
• the respiratory tract, diaphragm, and lungs form early in embryonic development

Question 2

How is the respiratory tract divided?

Answer 2

Respiratory tract is divided anatomically into 2 main part: 1) the upper respiratory tract, consisting of the nose, nasal cavity, and the pharynx
2) the lower respiratory tract consisting of the larynx, trachea, bronchi, and the lungs

• development of this system is not completed until the last weeks of fetal development

Question 3

Embryonic

Answer 3

• Week 4-5

- Features: lung buds originate as an outgrowth from the ventral wall of the foregut where lobar division occurs

Question 4

Pseudoglandular

Answer 4

• Week 5-17

- Features: Conducting epithelial tubes surrounded by thick mesenchyme are formed extensive airway branching

Question 5

Canalicular

Answer 5

• Week 16-25
• Features: Bronchioles are produced, increasing number of capillaries in close contact with cuboidal epithelium and the beginning of alveolar epithelium development

Question 6

Saccular

Answer 6

• Week 24 to 40

- Alveolar ducts and air sacs are developed

Question 7

Alveolar

Answer 7

• Late fetal to 8 years

- Features: Secondary septation occurs, marked increase of the number and size of capillaries and alveolin

Question 8

Trachea

Answer 8

• The endodermal lining of the middle segment of the laryngotracheal tube forms the epithelium and glands of the trachea
• mesenchymal cells surround the tracheal tube and ultimately form the cartilage, connective tissue, and smooth muscles of its walls
• by week 8 mesenchymal rudiments of the 16-20 tracheal cartilages are seen
• cilia appear at 10 weeks
• week 12 mucosal glands are seen and develop in a craniocaudal direction
• by the end of week 20 all major microscopic features of the trachea are visible

Question 9

Tracheoesophageal Fistula

Answer 9

posterior deviation of the tracheoesophageal septum can cause abnormal separation

Question 10

The bronchi

Answer 10

• In the fifth week the tracheal bud splits and forms two lateral outgrowths the bronchial bus
  0 it is at this early stage we the asymmetry of the lungs appear; the right bud forms three bronchi and the left two
• during week 5 each primary bronchus grows laterally into the medial walls of the pericardioperitoneal canals

Question 11

The pleura

Answer 11

• visceral mesoderm covering the outside of the bronchi develops into visceral pleura, and somatic mesoderm covering the inside of the body wall develops into parietal pleura

Question 12

Lung Maturation

Answer 12

• during the canalicular stage (16-25) the respiratory parts of the lungs develop
• canaliculi branch out from the terminal bronchioles

Question 13

Type 1 Alveolar epithelial cells

Answer 13

• flattened epithelium of endodermal origin

Question 14

Surfactant

Answer 14

• consists of glycerophospholipds, specific proteins, neural fats and cholesterol
• covers the alveolar surface and reduces the surface tension so that following birth the alevoli do not collapse during the expiration

Question 15

Respiratory Distress Syndrome

Answer 15

• occurs almost exclusively in premature infants
• develops because of impaired surfactant synthesis and secretion leading to atelectasis, ventilation-perfusion inequality, and hypoventilation with resultant hypoxemia and hypercarbia