Embryology - Respiratory System Development

Question 1

Describe the folding of the mesoderm?

Answer 1

Somatic mesoderm folds down to surround the splanchnic mesoderm of the intraembryonic body cavity/ coelom

Question 2

What does splanchnic mesoderm and somatic mesoderm form?

Answer 2

Somatic - parietal
Splanchnic - visceral

Question 3

What happen to yolk sac during folding of embryo laterally?

Answer 3

Yolk sac is absorbed into the primitive gut

Question 4

What does folding of embryo give rise to?

Answer 4

Primitive gut tube

Question 5

What does the gut tube form from?

Answer 5

Endoderm - foregut, midgut and hindgut

Question 6

Where do lung buds develop from?

Answer 6

Foregut

Question 7

Describe the formation of the trachea and lung buds

Answer 7

4 weeks - trachea and lung buds bud from wall of primitive foregut
Closely surrounded by splanchnic mesoderm

Question 8

What is the relationship between oesophagus and trachea?

Answer 8

Trachea is anterior to oesophagus

Question 9

What separates the trachea and lung buds from oesophagus

Answer 9

Oesophago-tracheal septum

Question 10

What happens if trachea and lung buds do not seperate?

Answer 10

Tracheoesophageal fistula and oesophageal atresia

Question 11

What is a fistula?

Answer 11

An abnormal passage between 2 epithelialized tubes or surfaces
TOF is common

Question 12

What is an atresia?

Answer 12

A condition which an orifice or passage in the body is closed or absent

Question 13

Describe the development of the pleura

Answer 13

Each lung bud invaginates the wall of the coelomic cavity and then grows to fill a greater part of the cavity

Question 14

What does pleura develop from?

Answer 14

Lateral plate mesoderm

Question 15

What forms the visceral pleura and parietal pleura?

Answer 15

Splanchnic forms visceral
Somatic forms parietal

Question 16

What is the pericardioperitoneal canal?

Answer 16

Space around lungs between somatic and splanchnic mesoderm is continuous with the pericardial and peritoneal cavity

Question 17

How is the sealing off of the pericardioperitoneal canal achieved?

Answer 17

Formation of pleuropericardial folds formed from the body wall and lines by somatic mesoderm
Once sealed off is known as pleural cavity

Question 18

What are the stages of development of the lungs?

Answer 18

Embryonic - lung bud develops
Foetal - pseudoglandular, canalicular and saccular
Postnatal - alveolar

Question 19

When is the pseudo-glandular stage?

Answer 19

7-17 weeks

Question 20

What is the pseudo-glandular stage?

Answer 20

Development of the lung except the respiratory part

Question 21

When is the canalicular stage?

Answer 21

17-27 weeks

Question 22

What is the canalicular stage?

Answer 22

Formation of respiratory part
Alveolar ducts form and epithelium starts to differentiate into type 1 and 2 pneumocytes
Still no gas exchange

Question 23

When is the saccular stage?

Answer 23

27-40 weeks

Question 24

What is the saccular stage?

Answer 24

Formation of the alveolar sacs, primitive alveoli and surfactant - gas exchange begins

Question 25

When is the alveolar stage?

Answer 25

32 weeks to 8 years postnatally

Question 26

What is the alveolar stage?

Answer 26

Proliferation of the alveoli from alveolar sacs

Question 27

Describe neonatal respiratory distress syndrome (hyaline membrane disease)

Answer 27

Caused by surfactant deficiency
Partial collapse of the alveoli
Debris consisting of blood elements accumulate to give glassy appearance

Question 28

What is lung agenesis caused by?

Answer 28

Failure of lung bud to develop/ branch
Insufficient mesoderm Teratogens

Question 29

Describe what is pulmonary hypoplasia

Answer 29

Incomplete development of the lungs, resulting in an abnormally low number or size of bronchopulmonary segments or alveoli

Question 30

What closes off the pleural cavities from the peritoneal cavity of the abdomen?

Answer 30

Pleuroperitoneal folds/ membranes forming the diaphragm

Question 31

What are the 4 mesodermal structures that the diaphragm develops from?

Answer 31

Septum transversum
Pleuroperitoneal folds
Skeletal muscle ingrowth from the peripheral body wall
The dorsal mesentery of the oesophagus

Question 32

What does the septum transversum form?

Answer 32

This forms the central tendon of the diaphragm

Question 33

Describe the pleuroperitoneal folds in the development of the diaphragm

Answer 33

Somatic mesodermal folds grow from peripheral body wall and fuse with septum transversum
They close off pleuroperitoneal canals - folds carry the lower intercostal nerves to supply the periphery of the diaphragm

Question 34

What does the skeletal muscle ingrowth from peripheral body wall form?

Answer 34

Covers the pleuroperitoneal folds thus forming the muscular part of the diaphragm
Somites C3-5 carry phrenic nerve to muscular part

Question 35

What does the dorsal mesentery of the oesophagus from of the diaphragm?

Answer 35

This structure attaches the embryological oesophagus to the posterior thoracic wall. Skeletal muscle from the periphery covers the dorsal mesentery to form the diaphragmatic crura.

Question 36

What are some abnormalities of the diaphragm?

Answer 36

Oesophageal hiatus - hiatus hernia
Foramen of Bochdalek and Morgagni - diaphragmatic hernia

Question 37

Explain a diaphragmatic hernia

Answer 37

Protrusion of n organ through the structure or muscle that usually contains it
Can compress left lung and push on heart and lungs

Question 38

What does diaphragmatic hernia result in?

Answer 38

Pulmonary hypoplasia