Respiratory Embryology

Question 1

The respiratory system begins as a median outgrowth known as:

Answer 1

Laryngotracheal groove

Question 2

Where is the laryngotracheal groove located?

Answer 2

The floor of the caudal end of the foregot/primordial pharynx and inferior to the 4th pharyngeal arches.

Question 3

Tracheobronchial tree develops…

Answer 3

Caudal to the 4th pharyngeal arches.

Question 4

Endoderm of laryngotracheal groove gives rise to:

Answer 4

Pulmonary epithelium, glands of pharynx, trachea, and bronchi.

Question 5

Splanchnic layer of lateral plate mesoderm gives rise to:

Answer 5

CT, cartilage, smooth muscle surrounding foregut.

Question 6

Laryngotracheal groove envaginates to form:

Answer 6

Laryngotracheal diverticulum (lung bud), which forms trachea and primary bronchial buds (2).

Question 7

Development of the lower respiratory system from endoderm

Answer 7

The diverticulum elongates and becomes invested in splanchnic mesenchyme.
The distal end enlarges to form respiratory bud (origin of respiratory tree).

Question 8

Tracheoesophageal folds

Answer 8

Fuse to form the tracheoesophageal septum.
Separates the esophagus and trachea.
Occurs end of week 5.

Question 9

Epithelial lining of the larynx is from:

Cartilage of the larynx is from:

Answer 9

Endoderm of laryngotracheal tube.

Mesenchyme of 4th and 6th pairs of pharyngeal arches (neural crest derived).

Question 10

Role of mesenchyme in development of the pharynx

Answer 10

Produces paired arytenoid swellings.

Converts the primordial glottis into T-shaped laryngeal inlet.

Question 11

Role of laryngeal epithelium in development of the larynx

Answer 11

It proliferates and occludes lumen of larynx.

Becomes recanalized in week 10 (forms the vocal folds/cords and vestibular folds at that time).

Question 12

Epiglottis develops from:

Answer 12

Hypopharyngeal eminence, which is produced from mesenchyme of 3-4th PAs.

Question 13

Laryngeal muscles develop from:

Answer 13

Myoblasts of 4th and 6th PAs.

Question 14

Laryngeal atresia

Answer 14

Birth defect resulting from a failure of recanalization of the larynx.
Causes obstruction of the upper airway, causing dilation of the airways and lung enlargement.
Diaphragm can become inverted.
Treatment in endoscopic dilation of the laryngeal web.

Question 15

Tracheoesophageal fistula

Answer 15

Abnormal connection between trachea and esophagus.
most common abnormality of LRT.
Commonly associated with esophageal atresia.
From failure of foregut endoderm to proliferate quickly enough in comparison to the rest of the embryo.
Pt cannot swallow, drools frequently, regurgitates when fed. Reflux can occur.
Polyhydramnios

Question 16

Polyhydramnios

Answer 16

Excess amniotic fluid.

Cannot enter the stomach/intestines for absorption.

Question 17

Where do the primary lung buds grow?

Answer 17

Into the Pericardioperitoneal canals.

Question 18

Primary bronchial buds branch in the ____ week and form secondary and tertiary bronchial buds.

Answer 18

5th

Question 19

Pattern of bronchi development (5 steps)

Answer 19

Main bronchi -> secondary bronchi -> lobar -> segmental -> intrasegmental branches.

Question 20

Stages of lung development (4)

Answer 20

Pseudoglandular (5-17 wks)
Canalicular (16-25 wks)
Terminal sac (24 wks-birth)
Alveolar (32 wks-8 yrs)

Question 21

Pseudoglandular stage

Answer 21

5 - 17 wks
Look like exocrine glands.
All major elements of lung have formed, except tose involved in gas exchange.
Fetus cannot survive.

Question 22

Canalicular stage

Answer 22

16 - 25 wks
Overlaps w/ pseudoglandular.
Vascularization occurs.
Respiratory bronchioles form.
Primitive alveoli form.
Possible survival.

Question 23

Terminal sac stage

Answer 23

24 wks - birth
Numerous alveoli form.
Thin epithelium w/ increased vascularization.
Type I/II pneumocytes form.
Lymphatic capillaries form.
Gas exchange occurs.
Survival.

Question 24

Alveolar stage

Answer 24

32 wks - 8 yrs
Alveolocapillary membrane forms.
Primitive alveoli become mature alveoli.
About 95% of mature alveoli occur postnatally.

Question 25

In the lungs, splanchnic mesoderm gives rise to:

Answer 25

Cartilaginous plates
Bronchial smooth muscle and CT
Pulmonary CT and capillaries

Question 26

Fetal breathing movements (FBMs)

Answer 26

Needed for normal lung development.
“Trains” respiratory muscles.
Used as a predictor of fetal outcome.
Needs to be forceful enough to case aspiration of amniotic fluid to stimulate lung development.

Question 27

FBMs cleared via (3):

Answer 27

Mouth/nose by pressure on the fetal thorax during vaginal delivery.
Pulmonary vasculature
Lymphatics

Question 28

Pulmonary agenesis

Answer 28

Complete absence of a lung or lobe and accompanying bronchi.

Respiratory bud fails to split.

Question 29

Oligohydramnios

Answer 29

Insufficient amniotic fluid production.

Severe or chronic oligohydramnios retards lung development.

Question 30

Pulmonary hypoplasia

Answer 30

Restriction of fetal thorax from uterine pressure.
Decreases hydraulic pressure on lungs.
Affects stretch receptors and lung growth.
Risks increase if coupled with oligohydramnios.

Question 31

Respiratory distress syndrome

Answer 31

Rapid, labored breathing develops shortly after birth.
Surfactant deficiency is major cause of RDS (irreversable damage to type II pneumocytes)
Sx: tachypnea, nasal flaring, costal abnormalities, grunting, cyanosis.

Question 32

Congenital lung cysts

Answer 32

Filled with fluid or air.
Thought to be formed by dilation of terminal bronchi.
May exhibit wheezing, cyanosis, difficulty breathing.