Respiratory Embryology Flashcards
What is the first structure in the formation of the respiratory system?
laryngotracheal groove
Where does the laryngotracheal groove form?
in the anterior portion of the foregut and primordial pharynx
-inferior to the 4th pharyngeal arches
What does the laryngotracheal groove morph into as it expands?
laryngotracheal diverticulum
In the respiratory system, what does the endoderm become?
- pulmonary epithelium
- glands of the larynx, trachea, and bronchi
In the respiratory system, what does the splanchnic mesoderm become?
- connective tissue
- cartilage
- smooth muscle
What is the structure that grows inward to separate the esophagus from the trachea?
tracheoesophageal fold
What does the tracheoesophageal fold become?
tracheoesophageal septum
What are the inner and outer linings of the esophagus and the trachea?
-endoderm surrounded by splanchnic mesoderm
What are the growths around the laryngeal groove that aid in transforming it into the laryngeal inlet?
arytenoid swellings
True or False: the laryngeal epithelium proliferates at such a rate that it occludes the laryngeal inlet at a point in time during development
True
What is the embryological process that re-opens the laryngeal inlet and when does it occur?
recanalization at 10 wks
Is the larynx of a neonate higher or lower than that of an adult?
higher
What is the embryological origin of the epiglottis?
hypopharyngeal eminence
-from mesenchyme of the 3rd and 4th pharyngeal arches
From what structures do the laryngeal muscles develop?
4th and 6th pharyngeal arches
True or False: in an infant, the epiglottis is in contact with the soft palate
True; it assists in the suckling reflex while nursing
What are two consequences of the larynx still descending over the course of a child’s first two years?
children are nosebreathers
children are at a higher risk of choking
What are the endodermal components of the trachea?
- trachea epithelium
- trachea glands
- pulmonary epithelium
What are the mesodermal components of the trachea?
- tracheal cartilages (hyaline)
- connective tissue
- smooth muscle
What is the role of the tracheoesophageal septum?
separation of respiratory and digestive system structures
During what week does the respiratory bud form and bifurcate into the primary bronchial buds?
week 4
During what week do the primary bronchial buds branch into the secondary bronchial buds?
week 5
During what week do the secondary bronchial buds branch into the tertiary bronchial buds?
week 7
During what week does the tracheoesophageal septum form?
week 5
What are the four stages of lung development?
1) pseudoglandular
2) canalicular
3) terminal sac
4) alveolar
What weeks comprise the pseudoglandular stage?
weeks 5-17
What are the characteristics during the pseudoglandular stage?
- histologically. the lung tissue looks like an exocrine gland
- all major elements have formed, except those involved with gas exchange
Can a fetus survive if born during the pseudoglandular stage of lung development?
No
What weeks comprise the canalicular stage?
weeks 16-25
What are the characteristics during the canalicular stage?
- vascularization
- formation of respiratory bronchioles
- formation of primordial alveolar sacs
Which parts of the lungs develops in advance of the other?
cranial segments advance in development before the caudal segments
Can a fetus survive if born during the canalicular stage of lung development?
some can
some can’t
What weeks comprise the terminal sac stage of lung development?
week 24 to birth
What are the characteristics of the terminal sac stage?
- numerous alveoli are forming
- thin epithelium w/ vascularization
- Type I and Type II pneumocytes
- gas exchange can occur
Can a fetus survive if born during the terminal sac stage of lung development?
Yes, but it depends on the production of surfactant and capillary development.
What weeks comprise the alveolar stage of lung development?
32 weeks to 8 yrs of age
What are the characteristics of the alveolar stage of lung development?
- primitive alveoli still forming
- mature alveoli exist
- new alveoli are formed
- largely completed by age 3 yrs
Can a fetus survive if born during the alveolar stage of lung development?
Yes
What cells produce surfactant?
Type II pneumocytes
What is the role of surfactant?
decrease surface tension of the lungs so that they can expand during breathing
Where is surfactant found in the body?
in the pleural cavity
Pathology: Laryngeal Atresia
- CHAOS (congenital high airway obstruction syndrome)
- dilated airways
- enlarged lungs filled w/ fluid
- diaphragm flattened or inverted
What is the embryological cause of laryngeal atresia?
failure of recanalization of larynx
What is the treatment for laryngeal atresia?
endoscopic dilation of the laryngeal web
Pathology: Tracheoesophageal Fistula
- abnormal connetion b/w esophagus and trachea
- most common congenital anomaly of the lower respiratory tract (1/4,000 live births)
Symptoms of a tracheoesophageal fistula
- cannot swallow
- frequently drool
-immediate regurgitation upon eating or gastric/intestinal contents may reflux into trachea/lungs
What is the most common form of a tracheoesophageal fistula?
-85% associated with an esophageal atresia
What is the embryologic cause of a tracheoesophageal fistula?
-failure of foregut endoderm to proliferate rapidly enough in relation to the rest of the embryo
What condition of pregnancy may accompany the presence of a tracheoesophageal fistula in a fetus?
polyhydramnios
- excess amniotic fluid bc it can’t enter fetal stomach
- fluid can’t be transferred via placenta for disposal
Pathology: Pulmonary Agenesis
1/15,000
- unilateral loss of a lung or a lobe of a lung and its accompanying bronchi
- respiratory bud fails to split into R/L bronchial buds
Pathology: Oligohydramnios
14/10,000
- insufficient amniotic fluid, <500 mL
- can retard lung development if chronic/severe
What fetal condition is often associated w/ oligohydramnios?
- renal agenesis
- renal failure
What fetal lung condition is associated with oligohydramnios?
- pulmonary hypoplasia
- d/t restriction of fetal thorax as a result of uterine pressure
When during pregnancy does oligohydramnios carry the greatest risk of pulmonary hypoplasia?
-prior to 26 weeks
What are some fetal characteristics caused by oligohydramnios?
- breech presentation
- positioning defects of hands and feet
Pathology: Respiratory Distress Syndrome
- rapid, labored breathing shortly after birth
- approx. 2% of infants
- 50-70% of deaths in premature infants
- surfactant deficiency
- underinflated lungs
Symptoms of Respiratory Distress Syndrome
- tachypnea or nasal flaring
- suprasternal, intercostal, or subcostal retractions
- grunting and cyanosis
What are characteristics of Respiratory Distress Syndrome?
- alveoli contain fluid that resembles a glassy membrane
- irreversible changes in Type II pneumocytes that make them incapable of producing surfactant
Pathology: Congenital Lung Cysts
- filled with fluid or air
- thought to be formed by abnormal dilation of certain segments of bronchi
Symptoms of Congenital Lung Cysts
- wheezing
- coughing
- difficulty breathing
