(15) Respiratory Embryology (Keim) Flashcards
The respiratory system primarily comes from which germ layer?
ENDODERM
Specifically, the respiratory system’s endoderm comes from…
the 6th paryngeal arch
*technically this is the foregut endoderm
What gives rise to the larynx and trachea?
Laryngotracheal diverticulum/groove
aka
Respiratory diverticulum
The inferior portion of the laryngotrachial diverticulum is also called:
The LUNG BUD
*Found on outside of embryo
What week does the respiratory system start to develop?
Week 4
What is occuring as the laryngotracheal diverticulum is forming during week 4?
The laryngotracheal diverticulum is forming the:
Esophagus
Stomach
The primitive trachea (laryngotracheal tube) and the esophagus are developing together in week 4. They need to be separated. How does this occur?
Tracheoesophageal folds meet the midline and form the tracheoesophageal septum.
This separates the esophagus from the laryngotracheal tube.
When is the tracheoesophageal septum complete?
Week 5
What type of structure is the tracheoesophageal septum?
Long structure longitudinally!!!
What does the larynx form from?
Foregut endoderm
6th Pharyngeal Arch
What are the structures you can identify to orient yourself to the 6th pharyngeal arch?
Bilateral arytenoid swellings
*remember! pharyngeal arch 6 is directly inferior to pharngeal arch 4
What are arytenoid swellings derived from?
Neural crest
covered with endoderm
What do the arytenoid swellings give rise to?
Cartilages in the larynx
What is the black wedge on top of the arytenoid swellings?
Glottis
What is the hypobranchial/hypopharyngeal eminence?
Region that develops the epiglottis
Which pharyngeal arches give rise to the hypobranchial/hypopharyngeal eminence?
Pharyngeal arches 3 and 4
When is epithelial occlusion w/ recanalization complete?
10th week
Congenital Abnormalities
What is:
Laryngeal Atresia?
Larynx is completly filled in as the result of failure of recanalization
Breathing is impossible; children present with asphyxia at time of birth
Requires an emergency tracheotomy
Congenital Abnormalities
What are:
Laryngeal Webs
Laryngeal webs are incomplete atresia, presenting as tissue between the vocal cords which blocks the glottis
Pts present with respiratory distress and stridor
Due to failure of recanalization (week 10)
Congenital Abnormalities
What is:
Laryngomalacia
Refers to a collapse of the supraglottic structures during inspiration
Most common congenital anomaly of the larynx
The tissue of the trachea comes from?
2 sources!!!
Pulmonary epithelium and glands = endoderm
Cartilage, connective tissue, smooth muscle = splanchnic mesoderm
What are tracheoesophageal (TE) fistulas?
Almost always associated with esophageal atresia = blind ended esophagus
Pts. struggle to feed
What is the cause of tracheoesophageal (TE) fistulas?
Failure of the tracheoesophageal folds to form in week 5
The lung bud forms out of the ____________ as the inferior portion of the ___________ at week ____.
The lung bud forms out of the foregut endoderm as the inferior portion of the laryngotracheal diverticulum at week 4
Bronchi and Lungs
State the structure that forms at the following week periods:
Week 4
Week 5
Week 6
Week 7
Week 24
Week 4 : : : Lung Bud
Week 5 : : : Primary Bronchial Buds
Week 6 : : : Seondary Bronchi
Week 7 : : : Tertiary bronchi
Week 24 : : : Terminal Bronchioles
Stages of Lung Development
What is the pseudoglandular stage?
Weeks 5-17
Terminal bronchioles formed, but NO ALVEOLI
Terminal bronchioles are surrounded by connective tissue
these pts. CANNOT SURVIVE
Stages of Lung Development
What is the Canalicular stage?
Weeks 16-25
Terminal bronchioles give rise to respiratory bronchioles which give rise to primodial alveolar ducts
Stages of Lung Development
What is the Terminal Sac stage?
Weeks 24-birth (32 weeks)
Type I and Type II pneumocytes formed
Surfactant is produced by Type II pneumocytes
Children born after 24 weeks will survive
Stages of Lung Development
What is the Alveolar stage?
32 weeks to 8 years
Form the Alveolocapillary membrane
Mature alveoli form
What is the order of stages of lung development?
Fetal Breathing Movements (FBMs)
What 3 things are essential for normal lung development?
- Fetal breathing movement itself
- Adequate thoracic space in the infant
- Sufficient quantity of amniotic fluid
Fetal Breathing Movements (FBMs)
What do fetuses breathe in utero?
Amniotic fluid
Fetal Breathing Movements (FBMs)
What events must occur in order to sucessfully transfer fetus from breathing amniotic fluid to breathing air upon birth?
Must clear the amniotic fluid at birth to start taking in air.
Assisted with vaginal canal pressure on the fetal thorax during vaginal delivery
Also occurs by draining of the amniotic fluid into pulmonary capillaries, arteries, veins as well as into lymphatics
_________ retards lung development and may result in pulmonary hypoplasia.
Risk significantly increased prior to ______ weeks.
Oligohydramnios
26
CASES:
What are signs and symptoms of Hyaline Membrane Disease (Respiratory Distress Syndrome)
Tachypnea
Nasal Flaring
Suprasternal, intercostal/subcostal retractions
Grunting
Cyanosis
What is your diagnosis?
Hyaline membrane disease/respiratory distress syndrome
What caused this presentation?
Reticulogranular ground glass appearance is due to…
LACK OF SURFACTANT that should have been produced by type II pneumocytes during the terminal sac stage
(Hyaline Membrane Disease/Respiratory Distress syndrome)
CASES:
What do you see?
Intestines in the thorax
Heart is displaced to the right because the intestines are in the thorax on the left
CASES:
What would be seen during physical examination with this patient?
- Barrel chest
- No breath sounds
- Scaphoid shaped abdomen
- Displaced heart sounds
CASES:
Student doctor…What is your diagnosis?
Congenital Diaphragmatic Hernia
(interchangeable names)
Foramen of Bochdalek
CASES
Infant presents with excessive secretions that cause drooling, choking, coughing, gaggling, respiratory distress and the inability to feed.
What is your potential diagnosis?
Tracheoesophageal Fistula
CASES:
What is the embryological mechanism that can explain this abnormality?
5th week tracheoesophageal septum in the 5th week was disrupted
CASES:
What is this X-ray revealing?
Congenital lung cysts
Honeycomb appearance on X-ray
