Development of the respiratory tract

Question 1

What are the five stages of the development of the respiratory tract?

Answer 1

Embryonic

Pseudoglandular

Canalicular

Saccular

Alveolar

Question 2

Which week does the respiratory tract start to develop?

Answer 2

Week 4

- starts with the development of the lung bud

Question 3

What begins the development of the lung bud?

Answer 3

The growth of the endodermal bud from the ventral wall of the gut tube

Question 4

Which structures make up the ventral lung bud and what does it develop from?

Answer 4

Makes up the larynx, trachea, lung

Form from the tracheoesophageal septum

Question 5

Which structure connects the dorsal foregut and the ventral lung bud?

Answer 5

Laryngeal orifice

Question 6

Which layer forms the epithelial lining of the lung bud?

Answer 6

Endodermal layer

however the lung bud grows into the surrounding mesoderm

Question 7

What does the mesoderm form which is important for the respiratory tract?

Answer 7

The cartilage and smooth muscle of the respiratory conduction pathway

Question 8

Which week do the tracheal bud split to form the bronchial buds?

Answer 8

The fifth week

Question 9

How many bronchi are formed on each bronchial bud?

Answer 9

Right = 3 bronchi

Left = 2 bronchi

Question 10

Which weeks do the psudoglandular stage take place?

Answer 10

Week 6 to 16

Question 11

How many generations of respiratory tree are there?

Answer 11

16 - 20

Question 12

What occurs during the pseudoglandular stage?

Answer 12

Resp tree continues to divide

Lung resembles a gland

Epithelial cells of the bronchial tree become ciliated and the beginning of the resp. elements appear

• cartilage and smooth muscle appears
• type 2 pneumocytes appear

Resp. tree including bronchioles have developed by the end of this stage

Question 13

Which weeks do the canalicular stage occur?

Answer 13

Weeks 17 - 24

Question 14

What occurs during the canalicular stage?

Answer 14

Resp. parts of lungs develop by:
- Canaliculi branch out from terminal bronchioles
- each form the primitive alveolus which consists of:
[] Acinus (sac-like cavity)
[] alveolar duct
[] a terminal sac

• duct widens, epithelial cells of the primitive alveoli flatten to form Type I pneumocytes
• capillaries invade the mesenchyme surrounding the primitive alveoli

Question 15

What is the main function of type 1 pneumocytes?

Answer 15

Gas exchange

Question 16

What is the saccular stage?

Answer 16

Terminal sac period, i.e. continued development of the resp. parts of the lungs

• type 2 pneumocytes
• more alveolar sacs develop from terminal bronchioles and alveolar ducts
• blood air barrier develops = exchange area increases

Question 17

When does the saccular stage take place?

Answer 17

Weeks 25 to birth

Question 18

What is the main function of type 2 penumocytes?

Answer 18

Produce surfactant

- prevents collapse of alveoli upon expiration

Question 19

When does the alveolar stage take place?

Answer 19

36 weeks onwards

Question 20

What occurs in the alveolar stage?

Answer 20

Alveoli increase in number and diameter

Type 1 pneumocytes continue to thin before birth, forming mature alveoli

Surfactant is produced in sufficient quantities for nomal lung function after birth

Question 21

What are the two classes of blood circulation present in the lungs?

Answer 21

Pulmonary

• derived from the artery of the 6th pharyngeal arch
• pulmonary vein lies more peripherally
• gas exchange => little blood flows through until birth

Bronchial

• supplies tissues of the lung
• direct branches of the paired dorsal aorta