4.1 Embryology of the Respiratory System
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How are the lungs formed?
How did the lungs grow?
- Lung buds made in wk 5
- Keeps growing and will be covered w/ mesoderm (gives rise to visceral and parietal pleura)
What are the stages of lung development?
- Pseudoglandular period (wk 5-16)
- Canalicular period (wk 16-26)
- Terminal sac period (wk 26-birth)
- Alveolar Period (8 mo - childhood)
What are the major events of the Pseudoglandular period?
- Week 5-16
- Branching has continued to form terminal bronchioles
- No respiratory bronchioles or alveoli are present
- Building up conducting zone but don't have respiration yet
What are the major events of the Canalicular period?
- Week 16-26
- Each terminal bronchiole divides into 2 or more respiratory bronchioles, which divide into 3-6 alveolar ducts
What are the major events of the Terminal sac period?
- Week 26 - birth
- Terminal sacs (primitive alveoli) form, and capillaries establish close contact
What are the major events of the Alveolar period?
- 8mo to childhood
- Mature alveoli have well developed epithelial endothelial (capillary) contacts
- 20-70 million alveoli at birth; 300-400 million by 8 yo
What is the embryological defects: tracheoesophageal fistulas?
- Esophagus doesn't lead to stomach
- Atresia - congenital absence or closure of a normal body orifice or tubular organ
- Fistula - abnormal or surgically made passageway between a hollow or tubular organ and the body surface, or between two hollow or tubular organs
What is the embryological defect: respiratory distress syndrome?
Deficiency or absence of surfactant
What are tx for respiratory distress syndrome?
- Corticosteroid administration prior to delivery
- Postnatal administration of artificial surfactant
- Postnatal high-frequency ventilation
What is the embryological defects: congenital diaphragmatic hernias?
- Bochdalek Hernia (85-90%) - left side affected
- Morgnani hernia - anterior location
- Right side closes first before left. And if it doesn't close, will get a hernia
What is the embryological defects: lung hypoplasia?
- Kidney development can impact lung development
- Kidneys help produce amniotic fluid and w/o it, the lung will be affected
What is another name for secondary bronchi?
What is another name for tertiary bronchi?
What is surgically significant about segmental bronchi?
Represent lungs that can be surgically resected
What is the smallest diameter bronchiole?
What is the conducting zone?
Conduit passage ways for air and does not support gas exchange
What is the first point in the bronchioles that allow for gas exchange?
Which germ layers contribute to the lungs?
- Endoderm - epithelial parts of lung
- Mesoderm - serous membranes of pleura, pericardium, peritoneum. Smooth muscle, cartilage, connective tissue components
What is the most important factors for the survival of premature infants?
- Establishing the blood-air barrier (begins in the late canicular period)
- Surfactant production
What is surfactant and how is it produced?
- Composed of phospholipids that decrease surface tension w/in the alveoli and prevent alveolar collapse
- Produced by Type II pneumocytes
What are the clinical symptoms of those who don't have surfactant?
- Inspiratory retractions of the chest wall
- Expiratory grunting
- Nasal flaring
Which vitamin is necessary for lung development and what happens when there isn't any?
- Vitamin A (RA - Retinoic Acid)
- Growth arrest
How is the diaphragm developed?
Intraembryonic coelom is initially a single space which is later divided into the pericardial, peritoneal, and pleural spaces
What are the changes that occur at birth?
- Aeration - replacement of lung liquid w/ air in the newborn's lungs (chest compression eliminates 1/3 fluid; adrenaline promotes absorption of the rest)
- Surfactant is released
- Fall in capillary pressure occurs w/ expansion of alveoli
- Respiratory movements of the chest begin
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