Respiratory System Embryo Flashcards
Where are the primitive pharynx, laryngotracheal groove and laryngotracheal diverticulum derived from?
Endoderm
When do the lung buds form?
Week 4
What are two other names for lungs buds?
Laryngotracheal diverticulum, respiratory diverticulum
What do the tracheoesophageal folds become?
Tracheoesophageal septum -> separating trachea (anteriorly) and esophagus (posteriorly)
When do tracheoesophageal folds appear?
Week 5
Where are the lungs, larynx and trachea derived from?
Foregut endoderm
Where are the artynoid swellings of the larynx derived from, and what are they comprised of?
Neural crest
They are cartilage covered in endoderm
What is the growth pattern of arytenoid swellings
They grow toward the tongue, first filling up the space where the future glottis will be, then apoptosis occurs creating “T” shapped opening of the glottis
What is recanalization and when does it occur?
Process of proliferation followed by apoptosis of the bilateral arytenoid swellings, which form the glottis and laryngeal ventricles
This happens during week 10
What are the 3 laryngeal abnormalities discussed?
- Laryngeal atresia
- Laryngeal webs
- Laryngomalacia
Describe laryngeal atresia and what it results from:
It is a full obstruction of the upper fetal airway, present with asphyxia at birth
It results from failure of recanalization during week 10 of development
Describe laryngeal webs, how they present and what they result from:
Incomplete atresia (type 4 is complete blockage), where tissue is present between vocal folds, blocking vocal cords. Present in infancy as respiratory distress and an unusal high pitched cry (stridor)
They result from failure of recanalization during week 10 of development
Describe layngomalacia
Most common congenital anomaly of the larynx (also called congenital laryngeal stridor)
We watched the video of this one: collapsing of the supraglottic structures during inspiration (airway open during expiration, but then collapses during inhalation)
What does endoderm in the trachea give rise to?
Epithelium, glands of trachea and pulmonary epithelium
What does splanchnic mesenchyme (mesoderm) give rise to in the trachea?
Cartilage, connective tissue, smooth muscles
What are the two variations of Tracheoesophageal fistulas?
- Esophageal atresia: most common - blind ended esophagus
- Tracheoesophageal fistula: abnormal passage between trachea and esophagus - this one harder to diagnose because its not as severe, but pts are prone to recurrent infections due to cross contamination b/w trachea and esophagus
Both caused by defect in tracheoesophageal folding during week 5.
What do the lung buds give rise to, and during what week of development?
R/L primary bronchi/bronchial buds during week 5
What do the primary bronchial buds give rise to, and during what week of development?
Secondary bronchi (3 on right, 2 on left) during week 6
What space do bronchiole buds grow into?
Pericardial peritoneal space
What do secondary bronchi give rise to, and during what week of development?
Tertiary bronchi (10 on right, 9 on left) during week 7
What week of development would we see terminal bronchioles, and how many branches?
By week 24, 17 orders of branches!
What are the 4 stages of lung development?
- Pseudoglandular (5-17 weeks)
- Canalicular (16-25 weeks)
- Terminal sack (24 weeks-birth)
- Alveolar (32 weeks-8 years)
What do you see during the pseudoglandular stage of lung development?
- terminal bronchioles, connective tissue and capillaries are formed, but capillaries are NOT in close proximity to terminal sacks -> so no gas exchange :(
- premi’s born during this stage cannot survive
What do you see during the canalicular stage of lung development?
- respiratory bronchioles continue proliferating to give primordial alveolar ducts
- also see terminal sacks (primitive alveoli), and better vascularization -> more surface area and vessels closer to terminal sacks means babies born during this stage have a better chance of survival (closer to 23-25 weeks)
What would you see during the terminal sack stage of lung development?
Squamous epithelium = Type I pneumocytes = gas exchange!
Secretory epithelial cells = Type II pneumocytes = surfactant!
Also see the formation of lymphatic capillaries. Infants born during this stage are very likely to survive
What is atelectasis?
Collapsing of the alveoli
What would you see during the alveolar stage of lung development?
- alveolar capillary membrane forms (endoderm and mesoderm)
- primitive alveoli continue proliferating to give more primitive alveoli
Note: 95% of mature alveoli form AFTER birth (usually by age 3, but up to 8 years). This is the reason why smoking around children is so dangerous
What are the 3 essential things for lung development?
- Fetal breathing movements
- Alveolar space (for lungs to grow)
- Amniotic fluid
What is Oligohydramnios?
Too little amniotic fluid: will retard lung development and the risk of developing pulmonary hypoplasia (low plasticity) increases significantly if low AF presents prior to 26 weeks
What is respiratory distress syndrome (aka hyaline membrane disease)? What does it look like on Xray and which lung developmental stage was messed up?
Caused by a lack of Type II pneumocytes (leading to a lack of surfactant) during the terminal sack stage of development. It looks like fuzzy ground glass in the lungs on an Xray
What is a congenital diaphragmatic hernia (aka Foramen of Bochdalek), and what stage of lung development went wrong?
Failure of septum transversum and pleuroperitoneal fold to fuse during week 6 of development. Will see intestine in thorax on Xray, barrel shaped chest, scaphiod appearing (sunk in) abdomen, absence of breath sounds and heartbeat displaced to the right
What are congenital lung cysts?
Cysts filled with either fluid or air, thought to result from disturbance in bronchial development during late fetal life. Will have a honeycomb appearance on Xray
What structure does the lower respiratory system develop from?
A single evagination from the anterior wall of the foregut
