Development of the Respiratory System

Question 1

When does the primordium of the tracheobronchial tree develop?

Answer 1

During week 4

Question 2

What starts as a median laryngotracheal groove in the caudoventral wall of the primitive pharynx?

Answer 2

Primordium of tracheobronchial tree

Question 3

What gives rise to the epithelium and glands of the larynx, trachea, bronchi, and the pulmonary epithelium?

Answer 3

The endoderm lining of the median laryngotracheal groove

Question 4

Connective tissue, cartilage, and smooth muscle of the larynx, trachea, and bronchi develop from what?

Answer 4

Splanchnic mesenchyme surrounding the foregut

Question 5

The laryngotracheal groove deepens into what?

Answer 5

A respiratory diverticulum ventrally

Question 6

The respiratory diverticulum enlarges distally into what?

Answer 6

A lung bud

Question 7

Where does the epithelial lining of the larynx develop from?

Answer 7

The endoderm of the cranial end of the laryngotracheal tube

Question 8

The cartilages of the larynx develop from where?

Answer 8

The cartilages in the 4th and 6th pairs of pharyngeal arches

Question 9

The laryngeal cartilages develop from where?

Answer 9

Mesenchyme that is derived from neural crest cells

Question 10

The mesenchyme at the cranial end of the laryngotracheal tube proliferates rapidly, producing what?

Answer 10

Paired arytenoid swellings

Question 11

The paired arytenoid swellings grow toward the tongue, converting the slitlike aperture, “the primordial glottis”, into what?

Answer 11

A T-shaped laryngeal inlet

Question 12

The laryngeal epithelium proliferates rapidly, resulting in?

Answer 12

Temporary occlusion of the laryngeal lumen

Question 13

Recanalization of the larynx normally occurs by when?

Answer 13

The 10th week

Question 14

Vocal cords develop from?

Answer 14

Folds of mucous membrane during the process of recanalization

Question 15

The epiglottis develops from?

Answer 15

The caudal part of the hypo pharyngeal eminence

Question 16

What is laryngeal atresia?

Answer 16

Rare anomaly resulting from failure of recanalization of the larynx, and causes obstruction of the upper fetal airway. AKA congenital high airway obstruction syndrome

Question 17

Laryngeal web results from?

Answer 17

Incomplete recanalization of the larynx causing partial airway obstruction

Question 18

The endodermal lining of the laryngotracheal tube distal to the larynx differentiates into?

Answer 18

The epithelium and glands of the trachea and the pulmonary epithelium

Question 19

The cartilage, connective tissue, and muscles of the trachea are derived from?

Answer 19

The splanchnic mesenchyme surrounding the laryngotracheal tube

Question 20

A tracheoesophageal fistula is an abnormal communication between the trachea and esophagus caused by?

Answer 20

A malformation of the tracheoesophageal septum

Question 21

Tracheoesophageal fistula is generally associated with?

Answer 21

Esophageal atresia (a condition in which a body orifice or passage in the body is abnormally closed or absent)
Polyhydramnious (too much amniotic fluid in the amniotic sac)

Question 22

Tracheoespophageal fistula results in?

Answer 22

Gaging and cyanosis after feeding, excessive accumulation of saliva or mucus in the nose and mouth, abdominal distention after crying, and reflux of gastric contents into lungs causing pneumonitis

Question 23

Tracheoesophageal fistula is most commonly located where?

Answer 23

Between the esophagus and distal third of the trachea

Question 24

The lung bud develops into what?

Answer 24

2 endodermal bronchial buds

Question 25

The 2 endodermal bronchial buds grow into what?

Answer 25

Pericardioperitoneal cavities and the primordial of the pleural cavities

Question 26

When do the bronchial buds enlarge into the primordial of a primary bronchus?

Answer 26

Early in week 5

Question 27

Which bronchial bud is slightly larger and is oriented more vertically?

Answer 27

The right bronchial bud

Question 28

The primary bronchi subsequently divides into what by week 7?

Answer 28

Secondary bronchi and then into tertiary bronchi

Question 29

What happens to the primary bronchi by week 24?

Answer 29

They divide another 14 times and respiratory bronchioles have developed

Question 30

Before birth, the bronchi will divide then another how many times before birth?

Answer 30

7 more times before birth

Question 31

As the bronchi develop, the surrounding mesenchyme synthesizes what?

Answer 31

The surrounding cartilages, smooth muscle, connective tissue, and capillaries

Question 32

The lungs acquire a layer of visceral pleura from where?

Answer 32

The splanchnic mesenchyme

Question 33

The splanchnic layer forms what?

Answer 33

The circulatory system and future gut wall

Question 34

The thoracic body wall becomes lined by what?

Answer 34

A layer of parietal pleura derived from the somatic mesoderm

Question 35

Maturation of the lungs is divided into what 4 periods?

Answer 35

1. Pseudo glandular period 2. Canalicular period 3. Terminal saccular period 4. Alveolar period

Question 36

Pseudo Glandular Period/Stage

Answer 36

Weeks 5-17 * Respiration is not possible * Premature fetuses cannot survive * Lungs look like an exocrine organ

Question 37

Canalicular Period/Stage

Answer 37

Weeks 13-25 * Overlaps with pseudo glandular period because cranial segments of the lungs mature faster than caudal ones * The lumen of the bronchi and terminal bronchioles become larger and the lungs become vascularized * Respiration is not possible * Premature rarely survive

Question 38

Terminal Sac Period/Stage

Answer 38

Weeks 24-birth * Type 1 & Type 2 pneumocytes are present * The epithelium becomes very thin * The intimate contact between epithelial and endothelial cells establishes the blood-air barrier * Respiration is possible * Premature fetuses born between weeks 25-28 can survive with intensive care

Question 39

Alveolar Period/Stage

Answer 39

Birth-8 years old * 95% of the mature alveoli develop after birth * Respiratory bronchioles, terminal sacs, alveolar ducts, and alveoli increase in number * Chest radiograph is more dense in children

Question 40

The blood-air barrier permits what?

Answer 40

Adequate gas exchange for survival of the fetus if it is born prematurely

Question 41

When does the production of surfactant increase?

Answer 41

During the last 2 weeks of pregnancy

Question 42

Type II pneumocytes secrete what?

Answer 42

Surfactant counteracting the surface tension forces and facilitating expansions of the terminal sacs

Question 43

Adequate pulmonary vasculature and sufficient surfactant are critical for what?

Answer 43

The survival of premature infants

Question 44

Developing lungs at birth are half filled with amniotic fluid. How is the fluid in the lungs cleared?

Answer 44

* through the mouth and nose by pressure on the thorax during delivery * into the pulmonary capillaries * into the lymphatics and pulmonary arteries and veins

Question 45

What 3 factors are important for normal lung development?

Answer 45

1. Adequate thoracic space for lung growth 2. Fetal breathing movements 3. Adequate amniotic fluid volume