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How are the lungs formed?
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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)
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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)
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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
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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
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What are the major events of the Terminal sac period?
- Week 26 - birth
- Terminal sacs (primitive alveoli) form, and capillaries establish close contact
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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
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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
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What is the embryological defect: respiratory distress syndrome?
Deficiency or absence of surfactant
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What are tx for respiratory distress syndrome?
- Corticosteroid administration prior to delivery
- Postnatal administration of artificial surfactant
- Postnatal high-frequency ventilation
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What is the embryological defects: congenital diaphragmatic hernias?
- Bochdalek Hernia (85-90%) - left side affectedÂ
- Morgnani hernia - anterior location
- Right side closes first before left. And if it doesn't close, will get a hernia
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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
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What is another name for secondary bronchi?
Lobar bronchi
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What is another name for tertiary bronchi?
Segmental bronchi
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What is surgically significant about segmental bronchi?
Represent lungs that can be surgically resected
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What is the smallest diameter bronchiole?
Terminal Bronchiole
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What is the conducting zone?
Conduit passage ways for air and does not support gas exchange
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What is the first point in the bronchioles that allow for gas exchange?
Respiratory bronchiole
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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
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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
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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
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What are the clinical symptoms of those who don't have surfactant?
- Dyspnea
- Tachypnea
- Inspiratory retractions of the chest wall
- Expiratory grunting
- Cyanosis
- Nasal flaring
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Which vitamin is necessary for lung development and what happens when there isn't any?
- Vitamin A (RA - Retinoic Acid)
- Growth arrest
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How is the diaphragm developed?
Intraembryonic coelom is initially a single space which is later divided into the pericardial, peritoneal, and pleural spaces
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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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