Respiratory embryology

Question 1

what does the respiratory system start as?

Answer 1

as a median outgrowth,

the laryngotracheal groove

Question 2

where does primordium of tracheobronchial tree develop?

Answer 2

caudal to 4th pharyngeal pouches

Question 3

where is laryngotracheal groove located?

Answer 3

floor of the caudal end of the foregut/primordial pharynx

Question 4

what does endoderm of laryngotracheal groove form?

Answer 4

pulmonary epithelium & glands of larynx, trachea, & bronchi

Question 5

what does Splanchnic mesoderm form?

Answer 5

CT, cartilage, & smooth muscle in these structures –surrounds the foregut

Question 6

how does lung bud form?

Answer 6

Laryngotracheal groove will evaginate

Question 7

what is the origin of the respiratory tree?

Answer 7

respiratory bud

Question 8

how is respiratory bud formed?

Answer 8

Diverticulum elongates & is invested w/ splanchnic mesenchyme

distal end forms bud

Question 9

what is tracheoesophageal septum, what does it do?

Answer 9

divides cranial part of foregut

into

ventral and dorsal

Question 10

how and when is tracheoesophageal septum formed?

Answer 10

week five

from Tracheoesophageal folds

Question 11

ventral part of foregut forms what?

Answer 11

laryngotracheal tube

primordium of larynx, trachea, bronchi, lungs

Question 12

dorsal part of foregut forms what?

Answer 12

primordium of oropharynx, esophagus

Question 13

where does epithelial lining of larynx come from?

Answer 13

endoderm of laryngotracheal tube (cranial end)

Question 14

where do Cartilages of larynx come from?

Answer 14

mesenchyme of 4th& 6thpairs of PAs

from ncc!

Question 15

explain the process by which laryngeal ventricles form?

Answer 15

Mesenchyme produces paired arytenoid swellings •Convert primordial glottis into a T-shaped laryngeal inlet

Laryngeal epithelium proliferates & occludes laryngeal lumen
•Recanalization occurs by 10th week

Question 16

how are vocal folds (cords) &vestibular folds formed?

Answer 16

folds of mucous membrane around laryngeal ventricles

Question 17

where does Epiglottis develop from, which PA in particular?

Answer 17

hypopharyngeal eminence

mesenchyme of the 3-4thPAs

Question 18

which PA do laryngeal muscles develop from?

Answer 18

4th& 6thPAs

Question 19

what separates respiratory & digestive tracts?

Answer 19

Epiglottis in contact w/ soft palate

Question 20

when does laryngeal descent occur?where is it in neonates

Answer 20

over the first 2 years

but its high in the neck in neonates

Question 21

what is laryngeal atresia?

Answer 21

Rare birth defect, resulting from failure of recanalization of the larynx

CHAOS SYNDROME: Obstruction of the upper fetal airway

Airways become dilated, lungs are enlarged & filled with fluid

Diaphragm flattened or inverted, & there is fetal ascites and/or hydrops

Question 22

how do you treat laryngeal atresia?

Answer 22

endoscopic dilation of the laryngeal web

Question 23

how does trachea develop?

Answer 23

Laryngotracheal diverticulum → trachea & primary bronchial buds (2)

Question 24

what respiratory structure does endoderm make?

Answer 24

tracheal epithelium & glands, & pulmonary epithelium

Question 25

what respiratory structure does splanchnic mesenchyme make?

Answer 25

tracheal cartilages, CT, & muscle

Question 26

what is a tracheoesophageal fistula?

Answer 26

abnormal connection between trachea & esophagus

Most common congenital anomaly of the lower respiratory tract

Failure of foregut endoderm to proliferate rapidly enough in relation to the rest of the embryo

esophageal atresia!!

Question 27

what are the effects of a tracheoesophageal fistula?

Answer 27

Cannot swallow, frequently drool saliva, immediate regurgitation when fed
•Gastric & intestinal contents may also reflux through the fistula into the trachea and lungs
•Polyhydramnios: excess amniotic fluid
•Cannot enter the stomach/intestines for absorption
•Not transferred for disposal via the placenta

Question 28

describe steps of lung development:

Answer 28

• respiratory bud develops in 4th week
• bud grows ventrocaudally, forms primary bronchail buds
• buds grow into pericardioperitoneal canal
• in 5th weekprimary bronchail buds form secondary bronchail buds, which form tertiary bronchail buds

Question 29

what is branching pattern in lung endoderm regulated by?

Answer 29

splanchnic mesoderm

Question 30

when and what form bronchopulmonary segments?

Answer 30

7th week

segmental bronchi + mesenchyme

Question 31

where does visceral pleura come from?

Answer 31

splanchnic portion of lateral plate mesenchyme

Question 32

where does parietal pleura come from?

Answer 32

somatic portion of lateral plate mesoderm

Question 33

when is pseudoglandular layer? can fetus survive? what is it?

Answer 33

5-17 weeks

lungs look like glands

lungs are formed, but no gas exchange elements

fetus can’t survive

Question 34

when is canaliclular layer? can fetus survive? what is it?

Answer 34

16-25 weeks

Vascularization happens

respiratory bronchioles form

Primordial alveolar & sacs present

may or may not survive

Question 35

when is terminal sac? can fetus survive? what is it?

Answer 35

24 weeks to birth

Numerous alveoli form

Thin epithelium w/increased vascularization

type 1 and type 2 pneumocytes form

gas exchange can occur, fetus can survive

Question 36

when is alveolar stage can fetus survive? what is it?

Answer 36

32wks -8yrs

• Alveolocapillarymembrane
• Primitive alveoli
• Form more primitive alveoli
• Mature alveoli

Question 37

when are most alveoli formed?

Answer 37

postnatally

up until 8 years of age

Question 38

why is splanchnic mesoderm imporant for bronchi development?

Answer 38

Form:

1. Cartilaginous plates (bronchial)
2. Bronchial smooth muscle & connective tissue
3. Pulmonary connective tissue & capillaries are also derived from this tissue

Question 39

how are fetal breathing movements important for lung development?

what is it used to measure?

Answer 39

Intermittent pattern that conditions respiratory muscles

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

Used during fetal monitoring & as a predictor of fetal outcome in preterm delivery

Question 40

how is intraalveolar fluid cleared at birth?

Answer 40

1. Released from mouth/nose by pressure on the fetal thorax during vaginal delivery
2. Pulmonary capillaries, arteries, & veins
3. Lymphatics

Question 41

what is pulmonary agenesis and how does it happen?

Answer 41

Unilateral agenesis: complete absence of a lung or a lobe & accompanying bronchi

Respiratory bud fails to split into R/L bronchial buds

Question 42

what is Oligohydramnios?

Answer 42

Insufficient amniotic fluid production (<500mL)

Typically associated with renal agenesis or failure

Severe & chronic oligohydramnios retards lung development

Question 43

what is Pulmonary hypoplasia?

Answer 43

restriction of fetal thorax

Decreased hydraulic pressure on the lungs

• Affects stretch receptors & lung growth
• Risks increases significantly with oligohydramnios

Question 44

what is potter sequence?

Answer 44

atypical physical appearance of a baby due to oligohydramnios experienced when in the uterus.

It includes clubbed feet, pulmonary hypoplasia and cranial anomalies related to the oligohydramnios

Question 45

what is Respiratory Distress Syndrome ?

Answer 45

Rapid, labored breathing develops shortly after birth

biggest cause of premature death!!

sulfactant defiency: lungs are underinflated

type II alveolar cells not working!

Question 46

what are the symptoms of RDS?

Answer 46

Tachypnea, nasal flaring

Suprasternal, intercostal, or subcostal retractions

Grunting & cyanosis

Question 47

what are Congenital Lung Cysts?

Answer 47

Filled with fluid or air

Thought to be formed by the dilation of terminal bronchi

Disturbance in bronchial development during late fetal life

may exhibit wheezing, cyanosis, difficulty breathing