Embryology

Question 1

What is the resp system an outgrowth of

Answer 1

Foregut endoderm

Question 2

What is the EPITHELIUM derived from

Answer 2

Foregut endoderm

Question 3

What does the SPLANCHNIC MESODERM give rise to

Answer 3

Connective tissue

Smooth muscle

Cartilages

Question 4

What will the outermost splanchnic mesoderm become

Answer 4

The visceral pleura that surrounds the lungs

Question 5

What gives rise to the parietal pleura

Answer 5

Somatic mesoderm

Question 6

Week of the EMBRYONIC phase

What does it develop

Answer 6

During the 4th week

Development of trachea and mainstem bronchi

Question 7

What are the last 4 phases of resp development associated with

Answer 7

The development of the distal airways and lungs

Question 8

After what week can a baby survive

Answer 8

22 weeks

Question 9

What does the embryonic phase begin with

Answer 9

An endodermal outgrowth of the foregut called the RESPIRATORY DIVERTICULUM

Question 10

What does the respiratory diverticulum become

Answer 10

The LARYNGOTRACHEAL TUBE with a swollen end called the TRACHEAL BUD

Question 11

What does the tracheal bud become

Answer 11

Trachea

Bronchi

Bronchioles

Lungs

Question 12

How do the trachea and oesophagus form

Answer 12

2 folds appear in the lateral wall of the laryngotracheal tube near its origin

=> TRACHEOESOPHAGEAL SEPTUM, separating the laryngotracheal tube in front from the developing oesophagus behind

Question 13

What happens as the tracheal bud elongates

Answer 13

The surrounding splanchnic mesoderm will differentiate to form the connective tissue, SM and cartilage found in the mature trachea

Question 14

What happens at the end of the 4th week

Answer 14

The tracheal bud branches to form the primary bronchial buds

As these buds grow laterally they grow into the pericardioperitoneal canal on each side, carrying a covering of splanchnic mesoderm with them

Pericardioperitoneal canals now become the PRIMITIVE PLEURAL CAVITIES

Question 15

Pathway of branching from the PRIMARY BRONCHIAL BUDS

Answer 15

1. Secondary (lobar) bronchii - 3 on the right and 2 on the left
2. Tertiary (segmental) bronchii - 10 on the right and 8 on the left - 7th WEEK

Then intersegmental bronchii, bronchioles, terminal bronchioles and respiratory bronchioles

Question 16

When do respiratory bronchioles first appear

Answer 16

24th week

By this time, there are about 17 generations of branches

Question 17

What happens as each generation branches

Answer 17

Surrounding mesenchyme differentiates to form the associated CT, SM and cartilage

Question 18

Weeks of the pseudoglandular phase

Answer 18

6-17 weeks

Resp portion of the resp system does not develop before this => foetus born before 16 weeks will not survive

Question 19

What part of the resp system is developing in the pseudoglandular phase

Answer 19

Conducting portion of the airway is developing

Question 20

Changes in structure during the pseudoglandular phase

Answer 20

Endodermal component differentiates into resp epithelium

Trachea and bronchii invaginates to form the tracheal and bronchial glands

Question 21

What forms around the developing epithelium

Answer 21

CT and SM and possibly cartilage

Question 22

Weeks of the canalicular phase

Answer 22

17-26 weeks

Respiratory portion of resp system develops

Question 23

Structural changes during canalicular phase

Answer 23

• 3 generations of branching of the terminal bronchioles occurs giving rise to the respiratory bronchioles opening into ALVEOLAR DUCTS
• The mesenchyme surrounding the respiratory bronchioles thins during further branching allowing the airspaces to widen

Question 24

As the alveolar ducts widen, what happens to the epithelium

Answer 24

Initially cuboidal, it thins so that many of its cells become squamous

these are TYPE I PNEUMOCYTES

Question 25

Name the remaining cuboidal cells of canalicular phase

Answer 25

Type II pneumocytes - accumulate lamellar granules storing surfactant

Question 26

What coincides with the formation of these squamous cells

Answer 26

A massive increase in the degree of vascularisation of the developing lung tissue, with many capillaries found in close association to the alveolar ducts

Question 27

What change occurs towards the end of the canalicular phase

Answer 27

terminal saccules appear at the ends of the alveolar ducts -\> definitive alveoli will develop from these technically gas exchange can occur so a foetus born after the 22nd week can survive

Question 28

Weeks of the terminal saccular phase

Answer 28

26 weeks-birth Period during which the definitive respiratory portion of the resp system develops

Question 29

What are the HIGHLY ATTENUATED walls of the alveoli in close contact with

Answer 29

The surrounding capillaries forming the blood-air interface

Question 30

What is CRUCIAL to the compliance of the alveoli

Answer 30

Elastic fibres deposited beneath the epithelium of the alveoli

Question 31

Where is surfactant secreted When does surfactant secretion markedly increase

Answer 31

Secreted onto the air surface of the alveoli The amount of surfactant increases markedly in the 2 weeks prior to birth

Question 32

When does surfactant production begin What happens at 28 weeks

Answer 32

Begins at 20 weeks It is not until 28 weeks or so that sufficient terminal saccules, alveoli and surfactant are present to permit survival of the premature foetus

Question 33

When does the alveolar phase begin

Answer 33

In the 32nd week when the first definitive alveoli appear and continues after birth to about 8

Question 34

What is the alveolar phase marked by

Answer 34

An increase in the number of alveoli An increase in the size of newly developed alveoli (Lung growth after birth is primarily due to increases in alveolar number)

Question 35

What are the developing lungs filled with

Answer 35

amniotic fluid

Question 36

Importance of amniotic fluid

Answer 36

* its presence is important for lung development * OLIGOHYDRAMNIOS - lung development does not occur fully due to insufficient amniotic fluid * Probably serves to drive expansion of the air spaces

Question 37

What does lack of surfactant cause

Answer 37

Respiratory Distress Syndrome = Hyaline Membrane Disease - alveoli contains fluid with a high protein content - resembles glassy or hyaline membrane on alveolar surface

Question 38

How can surfactant production be increased

Answer 38

By treatment with steroids, either before or after birth Surfactant can be administered exogenously after birth, greatly relieving RDS

Question 39

When do foetal breathing movements begin

Answer 39

Prior to birth, and these movements draw and expell amniotic fluid into and out of the lungs Allows resp muscles to function at birth

Question 40

What does the outermost layer of splanchnic mesoderm differentiate into

Answer 40

A layer of simple squamous mesothelium - visceral pleura, which is continuous at the lung root with the parietal pleura

Question 41

What is the parietal pleura

Answer 41

A layer of simple squamous mesothelium which differentiates from the somatic mesoderm and lines the walls of the pleural cavities