Embryology of respiratory system

Question 1

What happens at the end of week 4

Answer 1

The lateral body wall folds meet and fuse to close the ventral body wall
Cranial/caudal folding occurred due to rapid growth of the head and tail region
The gut tube is completely closed except where yolk sac is connected by vitelline duct

Question 2

What is gastroschisis

Answer 2

Failure of the body wall to close in the abdominal region resulting in intestinal loops herniating into the amniotic cavity

Question 3

What is ectopia cordis

Answer 3

When the lateral body folds fail to close in the thoracic region causing the heart to lie on the outside of chest wall

Question 4

What is bladder or cloacal exstropy

Answer 4

Abnormal body wall closure in the pelvic region

Cloacal extrophy is is more severe

Question 5

What three regions is the gut tube divided into

Answer 5

Foregut
Midgut
Hindgut

Question 6

When does the respiratory diverticulum appear

Answer 6

When the embryo is approx 4 weeks

Question 7

What is the respiratory diverticulum

Answer 7

Outgrowth of the foregut from its ventral wall
The epithelium present on the inner lining of the larynx, trachea, bronchi and the lungs is derived from endoderm
The rest of the lung tissue is derived from the visceral layer of the mesoderm

Question 8

How does the tracheoesophageal partitioning occur

Answer 8

Diverticulum starts to expand caudally
Causes two tracheoesophageal ridges to form
These grow towards each other and fuse to form the tracheoesophagael septum
Separating the foregut

Question 9

What is fistula

Answer 9

An abnormal connection or passageway that connects two organs or vessels that do not usually connect

Question 10

What is atresia

Answer 10

Absence or abnormal narrowing of an opening or passageway

Question 11

Where is the internal lining and the cartilages and muscles of the larynx derived from

Answer 11

Internal lining - endoderm

Cartilages and muscles are derived from the mesenchyme of the 4th and 6th pharyngeal arches

Question 12

What is a mesenchyme

Answer 12

Loosely organised, mainly mesodermal embryonic tissue that develops into connective and skeletal tissue

Question 13

What does the pharyngeal arches do

Answer 13

Gives rise to specific skeletal and muscular components of the head and neck, supplied by a particular cranial nerve, and its own artery

Question 14

How many pharyngeal arches are there

Answer 14

There are 5 arches

1,2,3,4 and 6

Question 15

What happens are the respiratory diverticulum separates from the foregut

Answer 15

Trachea as well as two primary bronchial buds form
At start of week 5, bronchial buds enlarge forming right and left primary bronchi
Then form 3 secondary bronchi of the right and 2 on the left
Then form 10 tertiary bronchi on right and 8 on the left

Question 16

What happens to the tertiary bronchi as lungs grow caudally

Answer 16

Further subdivision to form bronchioles which will continue to grow even in post natal life

Question 17

What are the 4 stages of lung maturation

Answer 17

Pseudoglandular
Canalicular
Terminal sac
Alveolar

Question 18

What is the pseudoglandular

Answer 18

Branching of the bronchial tree, forming many bronchioles up to terminal bronchioles
Bronchioles lined with cuboidal epithelium
Gas exchange not possible

Question 19

What is the canalicular

Answer 19

Each terminal branch divides into two or more respiratory bronchioles
These then divide into 3 to 6 alveolar ducts that become highly vascularised with capillaries
No gas exchange

Question 20

What happens at the start of terminal sac stage

Answer 20

Terminal sacs form
The epithelium of the terminal sacs is now a much thinner squamous epithelium
Capillaries establish close contact with the epithelium

Question 21

What happens from the 28 week onward regarding foetal breathing

Answer 21

Ther is sufficient numbers of alveolar sacs and capillaries to allow adequate gas exchange between air and primitive alveoli

Question 22

What happens in the last 2 months regarding terminal sacs

Answer 22

Number of terminal sacs increases

Question 23

How many terminal sacs are formed by birth in each lung

Answer 23

20-70 million

Question 24

What develops at the end of the 6th month during terminal sac stage

Answer 24

Type II alveolar epithelial cells develop

Question 25

What is surfactante

Answer 25

Essential lubricant for lung function
Forms phospholipid coat on the alveolar membranes
Lowers the surface tension at the air-alveolar interface, preventing the alveoli from collapsing

Question 26

What is respiratory distress syndrome

Answer 26

Absent or insufficient surfactant in premature babies

Primitive alveoli collapse causing respiratory distress syndrome

Question 27

What happens in alveolar stage

Answer 27

Mature alveoli form
Have well developed contact with capillaries as the epithelium lining thinned
After birth lungs grow due to increase in number of respiratory bronchioles and alveoli

Question 28

What is pulmonary hypoplasia

Answer 28

Reduced number of segments in the lung or alveoli

Question 29

Pulmonary agenesis

Answer 29

Absense of one or both lungs

Respiratory diverticulum fails to split into left and right bronchial buds and to continue growing