Test 2 (Lung Embryology) Flashcards
Explain the development of the Tracheoesophageal (respiratory) Diverticulum
- Development begins in Week 4 with formation of the Laryngeotracheal (Respiratory) Diverticulum.
- Outgrowth of Foregut (future esophagus) into the surrounding Splanchnic Mesoderm
- The original opening becomes the laryngeal orifice
- Surrounding MESENCHYME will become she supporting CARTILAGES!!!
- The Laryngeotracheal Diverticulum grows DISTALLY. Separated from Esophagus (Dorsally) by Tracheoesophageal Septum!!!
Which signaling molecules and transcriptions factor specify its position, growth, and development (Tracheoesophageal Diverticulum)?
- Location is determined by TBX4
- Linked to an INCREASE in RETINOID ACID produced by adjacent mesoderm
- It is expressed in the ENDODERM surrounding the foregut
- It induces FORMATION, GROWTH, and continued DIFFERENTIATION
Compare and contrast the contributions from Endoderm and Mesoderm
- Outgrowth of Foregut (future esophagus) into the surrounding Splanchnic Mesoderm
- The original opening becomes the laryngeal orifice
- Surrounding MESENCHYME will become she supporting CARTILAGES!!!
- The Laryngeotracheal Diverticulum grows DISTALLY. Separated from Esophagus (Dorsally) by Tracheoesophageal Septum!!!
ENDODERM: Epithelium of the Respiratory System
MESODERM: Connective Tissue, Cartilage, and Smooth Muscle
Describe the separation of the Respiratory and Gastrointestinal System
- Outgrowth of Foregut (future esophagus) into the surrounding Splanchnic Mesoderm
- The original opening becomes the laryngeal orifice
- Surrounding MESENCHYME will become she supporting CARTILAGES!!!
- The Laryngeotracheal Diverticulum grows DISTALLY. Separated from Esophagus (Dorsally) by Tracheoesophageal Septum!!!
What is the most common congenital abnormality associated with improper separation of the Esophagus and Trachea?
- Tracheoesophageal Fistula
- Abnormal communication between the Trachea and Esophagus
- Caused by IMPROPER formation of Tracheoesophageal Septum!!!
What abnormality of the Amniotic fluid, often detected on ultrasound, may be an indicator of this condition?
- Chest radiograph demonstrates an air-filled pouch representing the Proximal Esophagus.
- The distention of the Proximal segment is causing Anterior DISPLACEMENT of the Trachea
***** ESOPHAGEAL ATRESIA with TRACHEOESOPHAGEAL FISTULA and has an 87% recurrence!!!
***** Misexpression of TBX4 causes ectopic Endodermal budding and Trachea- Esophageal FISTULA!!!
- ** When an infant with the abnormality is fed, these infants SWALLOW normally but begin to cough and STRUGGLE as the fluid returns through the NOSE and MOUTH!!!
- The infant may be Cyanotic and may stop breathing as the overflow of fluid from the blind pouch is aspirated the Trachea and Lung
Describe the Branching pattern of the Lung Buds to Primary, Secondary, and Tertiary segmental Bronchi
- Left and Right Lung (Bronchial) buds form
- In week 5, they divide into the Bronchial buds
- These will become the PRIMARY BRONCHI
- Advanced stage of lobe development, end of week 6
- Secondary Bronchial Buds undergo a long series of branchings to form Respiratory Bronchioles
- The surrounding Mesenchyme also regulates the pattern of Branching of Lung Endoderm (Lining Epithelium)
- Pattern of segmentation also optimized to MINIMIZE RESISTANCE TO FLOW (Maximum area with Minimal Resistance)
**Parietal Pleura: SOMATIC
- **Visceral Pleura: SPLANCHNIC
- Splanchnic mesoderm differentiates into the SMOOTH MUSCLE, NERVES, and BLOOD VESSELS of the Lung
- **PULMONARY VEINS
- Single Pulmonary vein from POSTERIOR LEFT ATRIUM anastomoses with Veins forming in Mesoderm around developing Bronchioles
1) By 6 months, the Bronchi will divide into 17 Generations of Subdivisions
2) After birth there are an additional 6 divisions of the Bronchial Tree!!
3) As growth occurs, there is CAUDAL Development of the Lungs
4) At BIRTH the Tracheal bifurcation is at the level of T4!!!
Compare and contrast the stages of Lung Development.
1) Embryonic: (W4-7)
- Initial formation of Respiratory Diverticulum up to formation of ALL MAJOR BRONCHOPULMONARY Segments
- Differentiation of Pleura
2) Pseudoglandular: (W8-16)
- Major formation and growth of duct systems with Bronchopulmonary Segments
- INDUCTION of VASCULOGENESIS of Pulmonary Veins is through to be mediated by VASCULAR ENDOTHELIAL GROWTH FACTOR (VEGF), which is expressed in the Epithelium of TERMINAL BUDS in the Human Fetal Lung during the LATE PSEUDOGLANDULAR PHASE!
3) Canalicular: (W17-26)
- Formation of respiratory Bronchioles and Respiratory Sacs (Primitive Alveoli)
- Vascularization Increases
- Capillaries found in Walls
***SURFACTANT MADE FIRST TIME!!!!!
4) Terminal Sac: (W26 - 36)
- Alveoli or Terminal Sacs, develop from Respiratory Bronchioles
- Epithelium lining Alveoli differentiates into TWO CELL TYPES (Type I and Type II)
5) Postnatal (Alveolar): (W36 to Birth)
- Up to 90% of Alveoli formed after birth
- Primary mechanism of SEPARATION of Preexisting Alveoli
Which stage is viability possible?
- CANALICULAR STAGE because of the production of SURFACTANT!!!!!!!
What are the functional requirements that must be met for preterm infants to survive?
- Must be able to produce SURFACTANT!!!!!
- Weeks 24-26
Explain the functions of Type I and Type II Alveolar cells. pneumocytes and the roles of SURFACTANT and MACROPHAGES in preparation for Labor and Delivery
1) Type I:
- Form part of the Blood-air Barrier
2) Type II:
- Secretory cells that produce SURFACTANT
- Reduces SURFACE TENSION
- Facilitates ALVEOLAR EXPANSION
Describe Respiratory Distress Syndrome (RDS).
- Occurs primarily in Immature Lungs
- 60% of cases occur in infants born at less than 28 weeks
- 5% of cases occur in infants born at less than 37 weeks
- Labored Breathing
- DEFICIENCY/ ABSENCE of SURFACTANT!!!!!!!
- **Coats Alveoli and maintains Alveolar Patency
- ATELECTASIS is the Incomplete expansion or Collapse of Parts of or a whole Lung!!!
- **Histologic Examination: Alveoli are collapsed and the Alveolar ducts and Respiratory Bronchioles are DILATED!!!
- The lining of the Alveolar ducts is covered with FIRBIN-RICH HYALINE MEMBRANES (Damaged cells from collapsed Alveoli)
- Some RBC accumulate
What is the cause of RDS and current treatment?
- Deficiency in SURFACTANT!!!
- Give mother Glucoccortico Steroids to help treat!!!
Describe the primitive body cavity and how it is subdivided into Pleural, Pericardial, and Peritoneal cavities.
- Intraembryonic coelom is a continuous space
- Divide into Thoracic Cavity and Abdominopelvic cavity
- Further divided Thoracic Cavity into 1 Pericardial Cavity and 2 Pleural Cavities
- PLEUROPERICARDIAL MEMBRANES and DIAPHRAGM!!!
**PHRENIC NERVE sits inside the Pleuropericardial Membranes!!!!!!!!
What are the components of the Respiratory diaphragm?
1) Septum Transversum
2) Plemroperitoneal Membranes
3) Dorsal Mesentery of Esophagus
4) Lateral body wall (Cervical Somite Myotome)
***Week 4: Developing Diaphragm becomes Innervated by the PHRENIC NERVE (C3-5)
***Week 8: Descent of the Diaphragm to L1
