Embryology 3

Question 1

What are the 4 sections the development if the respiratory system is divided into?

Answer 1

1) Trachea
2) Lungs
3) Pleura
4) Diaphragm

Question 2

What happens during the lateral folding of the embryo?

Answer 2

The somatic (parietal) mesoderm folds down to surround the
splanchnic (visceral) mesoderm of the intraembryonic body cavity/coelom.

The yolk sac becomes absorbed into the primitive gut .

Question 3

Where does the trachea and the lungs develop from?

Answer 3

FOREGUT part of the primitive gut tube

Question 4

What does folding of the embryo give rise to?

Answer 4

The primitive gut tube

Question 5

What does the gut tube form from?

Answer 5

Endoderm –> foregut, midgut, hindgut

Question 6

What happens at week 4?

Answer 6

Trachea and lung buds bud out from the ventral/anterior wall of the primitive foregut (endoderm).

Question 7

What is the trachea and lung buds closely surrounded by?

Answer 7

Lateral plate splanchnic (visceral) mesoderm.

Question 8

What does the foregut endoderm give rise to?

Answer 8

Lung bud

Question 9

What does the lung bud give rise to?

Answer 9

Trachea and lungs

Question 10

What will the pleura arise from?

Answer 10

The lateral plate mesoderm surrounding the lung bud

Question 11

What develops between oesophagus and trachea completely separating them?

Answer 11

OESOPHAGOTRACHEAL SEPTUM –> ventral trachea and dorsal oesophagus

Question 12

What if the trachea and oesophagus dont separate?

Answer 12

Tracheoesophageal fistula (TOF) and Oesophageal Atresia
- a common congenital abnormality

Question 13

What type of condition is FISTULA?

Answer 13

an abnormal passage between 2 epithelialized tubes or surfaces.

Question 14

What type of condition is ATRESIA?

Answer 14

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

Question 15

How is the pleural cavity formed?

Answer 15

Lung buds will push the splanchnic mesoderm towards the somatic mesoderm and become completely surrounded by both layers. The space between the two layers
will become the pleural cavity.

Question 16

splanchnic layer of lateral plate mesoderm forms…

Answer 16

visceral pleura

Question 16

What is the pericardioperitoneal canal

Answer 16

the space between the splanchnic and somatic mesoderm around the lungs is initially continuous with the pericardial and peritoneal cavity.

Question 16

Somatic layer of lateral plate mesoderm forms…

Answer 16

Parietal pleura

Question 17

How is the correct ventilatory pleural cavity pressures maintained?

Answer 17

Periocardioperitoneal canal is sealed off from the pericardial and peritoneal cavities by the formation of the pleuropericardial folds formed from the body wall and lined by somatic mesoderm
THE PLEURAL CAVITY IS NOW FORMED

Question 18

Describe the 3 stages within the FETAL PERIOD

Answer 18

1. Pseudoglandular stage (7 -17 weeks).
   - Development of lung except respiratory part (no gas exchange)
2. Canalicular stage (17-27 weeks).
   - Formation of respiratory part. Alveolar ducts form and epithelium starts to differentiate into Type I and Type II pneumocytes (still no gas exchange).
3. Saccular stage (27-40 weeks).
   - Formation of alveolar sacs, primitive alveoli and surfactant (gas exchange begins).

Question 19

What happens during the POSTNATAL period

Answer 19

4. Alveolar stage (32 weeks to 8 years).
   - Proliferation of alveoli from alveolar sacs.
   - About95% of adult alveoli formed postnatally. 300m alveoli in adult

Question 20

Name 3 congenital lung condition

Answer 20

Neonatal Respiratory Distress Syndrome (Hyaline Membrane Disease)

LUNG AGENESIS

PULMONARY HYPOPLASIA

Question 21

What is neonatal respiratory distress syndrome caused by?

Answer 21

surfactant deficiency
partial collapse of alveoli
Debris consisting of blood elements accumulate – glassy (hyaline membrane) appearance

Question 22

What is lung agenesis caused by?

Answer 22

• Failure of lung bud to develop/ branch
• Insufficient mesoderm
• Teratogens

Question 23

What is pulmonary hypoplasia caused by?

Answer 23

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

Question 24

What does the diaphragm develop from?

Answer 24

4 mesodermal structures

Question 25

How does the septum transversum form?

Answer 25

This forms the central tendon of the diaphragm

Question 26

How does the Pleuroperitoneal folds form?

Answer 26

These somatic mesodermal folds grow in from the peripheral body wall to fuse with septum transversum. They close off the pleuroperitoneal canals, thus separating the pleural cavities from the peritoneal cavity. (Failure of these folds to form can result in herniation of adominal contents into the thorax). These folds carry the lower intercostal nerves to supply the periphery of the diaphragm

Question 27

How does skeletal muscle ingrowth from the peripheral body wall grow?

Answer 27

This grows inwards to cover the pleuroperitoneal folds thus forming the muscular part of the diaphragm. From somites C3-C5 – these carry the phrenic nerve to the muscular part (phrenic nerve roots = C3, C4, C5.

Question 28

What does the dorsal mesentery of the oesophagus attach?

Answer 28

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 29

What forms the central tendon of the developing diaphragm?

Answer 29

Septum transversum

Question 30

What happens if there is a failure of diaphragm to completely close during development?

Answer 30

Protrusion of an organ through the structure or muscle that usually contains it.