Respiratory Embryology

Question 1

When does the development of the respiratory system start and end

Answer 1

about the 4th week it begins

alveoli will continue to form through the 8th year of life

Question 2

Where and how does the Respiratory system begin on the embryo

Answer 2

Starts as a median outgrowth known as the Laryngotracheal groove

this is found in the floor of the caudal end of the foregut

inferior to the 4th pharyngeal arches

the primordium of tracheobronchial tree will develop caudal to the 4th pharyngeal pouches

Question 3

What does the Endoderm of the laryngotracheal groove give rise to

Answer 3

Pulmonary epithelium, and glands of larynx, trachea, and bronchi

Question 4

What does the splanchnic mesoderm from the lateral plate give rise to in the respiratory system

Answer 4

CT, cartilage, smooth muscle in these structures and surrounds the foregut

Question 5

How does the respiratory bud form

Answer 5

Laryngotracheal groove will evaginate to form the laryngotracheal diverticulum (lung bud)

this will then elongate and become invested with splanchnic mesenchyme

then the distal end of the laryngotracheal diverticulum will enlarge to form a globular respiratory bud (the orgin of the respiratory tree)

Question 6

What is the function of the Tracheoesophageal folds and when do they develop

Answer 6

these tracheoesophageal folds will fuse to form the tracheoesophageal septum at the end of the 5th week

these will divide the cranial portion of the foregut

the Ventral part: becomes the laryngotracheal tube (larynx, trachea, bronchi, lungs)

the dorsal part: oropharynx, esophagus

Question 7

How does the development of the larynx occur

Answer 7

at the laryngotracheal groove, mesenchyme produces arytenoid swellings making a T shaped laryngeal inlet

laryngeal epithelium will then proliferate and occlude the lumen, however this will recanalize at the 10th week of the embryo development

during recanalization, laryngeal ventricles will form to create the vocal folds and vestibular folds

Question 8

How does the Epiglottis form and what is it in contact with in the mouth

Answer 8

develops from the hypopharyngeal eminence which is produced from mesenchyme of the 3rd and 4th Pharyngeal arches

in contact with the soft palate to separate the respiratory and digestive tracts

Question 9

What does the Laryngeal muscles develop from and what happens to the larynx during the first two years

Answer 9

Laryngeal muscles develop from the Myoblasts of the 4th and 6th Pharyngeal Arches

the larynx is in a high position in the neck of the neonate and then in the first 2 years the laryngeal will descend

Question 10

Laryngeal atresia

Answer 10

Failure of recanalization of the larynx

Obstruction of the upper fetal airway or congenital high airway obstruction syndrome (CHAOS Syndrome)

lungs filled with fluid
diaphragm flattened or inverted and there are fetal ascites or hydrops

treatment is by endoscopic dilation of the laryngeal web

Question 11

Tracheosophageal fistula

Answer 11

an abnormal connection between the trachea and the esophagus

most common congenital anomaly of the lower respiratory tract

caused by a failure of the foregut endoderm to proliferate rapidly enough in relation to the rest of the embryo

cases usually associated with esophageal atresia: blind esophagus

cannont swallow, frequently drool, immediate regurgitation when fed

Polyhydraminos: excess amniotic fluid

• due to not transferred for disposal via the placenta
• cannot enter the stomach/intestines for absorption

Question 12

How do the lungs develop

Answer 12

Distal end of the laryngotracheal diverticulum enlarges to form the respiratory bud in the 4th week

the bud will grow ventrocaudally and bifurcate to make the primary bronchial buds

then they will grow laterally into the pericardioperitoneal canals

Question 13

when does the branching of the primary bronchial buds begin, and what dictates the branching pattern

Answer 13

5th week goes to the secondary bronchial buds and then to the tertiary bronchial buds

the branching patterns of the lung endoderm is regulated by the splanchnic mesenchyme

bronchopulmonary segments occur in the 7th week which is due to the segment bronchi and the mesenchyme

Question 14

What is the Visceral and parietal pleura developed from

Answer 14

Visceral pleura: splanchnic portion of lateral plate mesenchyme

Parietal Pleura: somatic portion of lateral plate mesoderm

Question 15

What are the 4 steps of the Lung Maturation and what weeks are they when they appear

Answer 15

Pseudoglandular: 5-7 weeks

Canalicular 16-25 weeks

Terminal Sac: 24weeks to birth

Alveolar: 32 weeks to 8 years

Question 16

Lung Maturation: Pseudoglandular

Answer 16

Looks like exocrine glands

all major elements of the lung have formed except those involved with gas exchange

fetus cant survive

Question 17

Lung Maturation: Canalicular

Answer 17

Overlaps pseudoglandular

Vascularization

Respiratory bronchioles

Primodial alveolar and sacs are present

+/- survival

Question 18

Lung Maturation: Terminal Sac

Answer 18

Numerous alveoli form

thin epithelium w/increased Vascularization

• type 1 and type II pneumocytes
• lymphatic capillaries

gas exchange can occur

survivable

Question 19

Lung Maturation Alveolar

Answer 19

Alveolocapillary membrane
primitive alveoli
form more primitive alveoli
mature alveoli

Question 20

What are the three things that splanchnic mesoderm is critical in developing for the bronchi development

Answer 20

Cartilaginous plates

Bronchial smooth muscle and connective tissue

Pulmonary connective tissue and capillaries are aslso derived from this tissue

Question 21

What year is alveolar development largely completed

Answer 21

3 years

Question 22

what are the three ways that intra-alveolar fluid is cleared

Answer 22

Released from mouth/nose by pressure on the fetal thorax during vaginal delivery

pulmonary capillaries, arteries and veins

lymphatics

Question 23

What are Fetal Breathing Movements

Answer 23

Essential for normal lung development

intermittent pattern that conditions respiratory muscles

also used during fetal monitoring and as a predictor of fetal outcome in pre term delivery

Forceful enough to cause aspiration of amniotic fluid and helps stimulate lung development

Question 24

Pulmonary Agenesis

Answer 24

Unilateral agenesis of a complete lung or a lobe and accompanying bronchi

respiratory bud fails to split into R/L bronchial buds

Question 25

Oligohydramnios

Answer 25

insufficient amniotic fluid production

associated with renal agenesis or failure

if severe enough can retard lung development

Pulmonary hypoplasia: restriction of fetal thorax from uterine pressure affecting lung growth

Potters Sequence

Question 26

Respiratory distress syndrome

Answer 26

surfactant deficiency is major cause

lungs are underinflated

due to irreversible changes in the Type II alveolar cells making them incapable of producing surfactant

Tachypnea, nasal flaring, grunting, nasal flaring

Question 27

Congenital Lung Cysts

Answer 27

filled with fluid or air

formed by the dilation of terminal bronchi
due to disturbance in bronchial development during late fetal life

may exhibit wheezing, cyanosis, difficulty breathing