Development of the Lung Flashcards
What tissues of the respiratory tract arise the endoderm? What tissues arise from the (splanchnic) mesoderm?
Endoderm: epithelial linings of the larynx, trachea, bronchi, and lungs Mesoderm Cartilage, Smooth Muscle, Elastic and Fibrous Connective tissue
What is the laryngotracheal tube? What structures does it turn into?
A combined tube that will turn into the esophagus and the trachea when separated by the tracheoesophageal septum
What is the first tracheal division? How many divisions are there? What is the second tracheal division? How many divisions are there?
Primary Bronchi; 1 on the left, 1 on the right Lobar Bronchi; 3 on the right, 2 on the left
What can occur from abnormal or insufficient development of the tracheoesophageal septum?
tracheoesophageal fistulas various types, all have weird connection between stomach, trachea, and esophagus
How are tracheoesophageal defects evaluated?
X-ray (look for gas in bowels) Contrast study Bronchoscopy
What are some anomalies associated with abnormal tracheoesophageal septum formation? Which TE septum abnormalities are most likely to have associated abnormalities?
Cardiac abnormalities; renal agenesis, dysplasia, or horseshoe; hemi-vertebrae; intestinal atresia, malformation Most common with esophageal atresia and least common with transesophageal fistulas.
What is the biggest determiner of survival for patients with TEF disorders?
Birth weight (and presence of cardiac defect)
What occurs during the pseudoglandular phase? When does this take place?
Airway branching continues, capillaries begin to form week 6-16
What occurs during the canalicular phase? When does this take place?
Capillary density increases, pneumocytes differentiate week 16-26 (The end of this phase is the beginning of extrauterine viability)
What occurs during the terminal sac phase? When does this take place?
Distal airways dilate, terminal sacs form, elastic fibers form, epithelium thins week 26-Birth
What is Congenital Cystic Adenomatoid Malformation (CCAM)?
Overgrowth of bronchial tissue compared to surrounding mesenchyme; this limits the lung development as the CCAM will never be functional lung
What are the three classifications of CCAM?
Type I- large macroscopic cysts Type II- small macroscopic cysts Type III-microscopic cysts
What are potential symptoms of CCAM?
- Respiratory distress
- Recurrent lung infections (pneumonia w/ abcess formation is a major concern)
- pulmonary hypoplasia
- pulmonary hypertension
- mediastinum distortion
- imparied venous returns
- hydrops fetalis
- Asymptomatic (ultrasound abnormalities)
- How much of the lung is affected in CCAM?
- How is CCAM treated?
- Usually affects only a single lobe
- Treatment:
- Intubation to improve hypoxemia
- Thoracotomy & Lobectomy
What is hydrops fetalis / prenatal hydrops?
How is prenatal hydrops treated?
Prenatal hydrops is edema within at least two compartments in a fetus.
Options:
- Thoracocentesis
- Thoracoamniotic shunt
- Fetal lobectomy
- Induce delivery & perform resection
Why is it recommended that CCAMs are almost always resected within the first 3-6 months of life (3 reasons)?
- CCAMs can cause recurrent infections; resection of symptomatic lesions are more difficult
- There is always diagnostic uncertainty before a pathologic specimen is available
- Cancers can develop in CCAMs at as little as 1 year of age
- When is the alveolar phase of lung development?
- What occurs during this phase?
- When do most alveoli form?
- 32 weeks - 8 years
- Alveolar formation occurs via subdivision of terminal sacs aka septation. The alveolar septa (walls) become thinner.
- Most alveoli form after birth
- Are phases of lung development distinct or overlapping?
- What is the direction of lung development?
- When does functional lung tissue form in comparison to funcitonal tissues in many other organs?
- Overlapping
- Proximal to distal (aka centrifugal)
- Functional lung tissue develops relatively late (we don’t use ‘em much before we’re born!)
The prenatal lung contains fluid. What happens when the prenatal lung produces an insufficient amount of fluid? Why?
Hypoplastic Lung
The fetus has shallow and episodic respiratory movements during development wherein the fluid helps to stretch the lungs out. Less fluid = less stretching = small lungs.
- What is wet lung?
- How does it present? When?
- How is it treated?
- Wet lung is a problem with fluid removal from the lungs after birth.
- Transient tacypnea. Presents immediatelly or within hours of birth, lasts a few hours to two days
- Typically a transient condition. Supportive care if needed.
- What produces pulmonary surfactant?
- When does this production begin?
- Why is this important in terms of preterm babies?
- Type II pneumocytes
- Begins toward end of the canalicular period, with significant increase in production at 35 weeks
- Prior to 35 weeks, usually insufficient surfactant to support extrauterine life
What are the three major components of surfactant?
- Phospholipid
- Dipalmitoylphosphatidylcholine
- Dipalmitoylphosphatidylglycerol
- Protein
- Antioxidant
Name 7 clinical signs of respiratory distress.
- Rapid breathing (>60/min in infant)
- Flaring nostrils
- Chest retractions
- Expiratory grunt
- Often cyanotic
- Tachycardia
- Anxious expression
- In what context is Respiratory Distress Syndrome typically seen?
- What is its other name?
- What is the central problem in RDS?
- What pathologic changes to the lungs occur in RDS?
- Usually premature with immature lungs
- aka Hyaline membrane disease
- inability to keep alveoli filled with air
- Pathologic changes:
- Poor lung tissue compliance
- Alveolar collapse causes atelectasias
- Engorgement of pumonary capillaries
- Formation of Hyaline Membranes
