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Questions and Answers
What marks the beginning of the development of the respiratory passages during gestation?
What marks the beginning of the development of the respiratory passages during gestation?
Which phase of lung development is characterized by the appearance of Clara cells and endocrine cells?
Which phase of lung development is characterized by the appearance of Clara cells and endocrine cells?
What is the primary function of type II pneumocytes that arise during the 28th week of gestation?
What is the primary function of type II pneumocytes that arise during the 28th week of gestation?
Which cell type is NOT typically found in the early development of the respiratory epithelium?
Which cell type is NOT typically found in the early development of the respiratory epithelium?
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During which phase do the respiratory bronchioles begin to develop into tubes lined by flattened epithelium?
During which phase do the respiratory bronchioles begin to develop into tubes lined by flattened epithelium?
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In the glandular phase of lung development, what do the columnar cells primarily contain?
In the glandular phase of lung development, what do the columnar cells primarily contain?
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Which statement accurately describes the changes in type II pneumocytes as they mature?
Which statement accurately describes the changes in type II pneumocytes as they mature?
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During which phase do the terminal buds transform from being spherical and become less so?
During which phase do the terminal buds transform from being spherical and become less so?
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When is the adult number of alveoli typically reached?
When is the adult number of alveoli typically reached?
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Which of the following structures is primarily responsible for the lining epithelium of the respiratory tract?
Which of the following structures is primarily responsible for the lining epithelium of the respiratory tract?
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Which adaptation is NOT necessary for the transition from placental to autonomous gas exchange?
Which adaptation is NOT necessary for the transition from placental to autonomous gas exchange?
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Identify the image that best represents the differentiation of lung structures during gestation.
Identify the image that best represents the differentiation of lung structures during gestation.
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What type of intercellular junctions are found between the epithelial cells in the early stages of lung development?
What type of intercellular junctions are found between the epithelial cells in the early stages of lung development?
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What type of epithelium lines the developing alveoli more closely associated with capillaries?
What type of epithelium lines the developing alveoli more closely associated with capillaries?
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Identify the stage where the lumina of bronchi and terminal bronchioles are enlarging.
Identify the stage where the lumina of bronchi and terminal bronchioles are enlarging.
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What is the primary origin of the epithelium and glands of the trachea?
What is the primary origin of the epithelium and glands of the trachea?
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What happens to the septa between capillaries as the lungs develop?
What happens to the septa between capillaries as the lungs develop?
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Which structure is formed as the laryngotracheal groove evaginates?
Which structure is formed as the laryngotracheal groove evaginates?
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Which mesoderm is responsible for the cartilage, connective tissue, and muscles of the trachea?
Which mesoderm is responsible for the cartilage, connective tissue, and muscles of the trachea?
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At what week of development do the lower respiratory organs begin to form?
At what week of development do the lower respiratory organs begin to form?
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Which pair of pharyngeal arches contribute to the muscle and cartilage of the larynx?
Which pair of pharyngeal arches contribute to the muscle and cartilage of the larynx?
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Which structures develop from the primary bronchial buds?
Which structures develop from the primary bronchial buds?
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What layer is formed from the splanchnic mesenchyme during lung development?
What layer is formed from the splanchnic mesenchyme during lung development?
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Which of the following structures does NOT develop from the laryngotracheal diverticulum?
Which of the following structures does NOT develop from the laryngotracheal diverticulum?
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Study Notes
Development of the Respiratory System
- The lower respiratory organs (larynx, trachea, bronchi, and lungs) develop during the fourth week of development.
- The tracheobronchial tree develops caudal to the fourth pair of pharyngeal pouches.
- The endoderm lining the laryngotracheal groove forms the pulmonary epithelium and glands of the larynx, trachea, and bronchi.
- Connective tissue, cartilage, and smooth muscle develop from the splanchnic mesoderm.
- By the end of the fourth week, the laryngotracheal groove evaginates to form a laryngotracheal diverticulum (lung bud).
Laryngotracheal Diverticulum
- The laryngotracheal diverticulum separates from the foregut to form the trachea and two lateral outpouchings (primary bronchial buds).
- The endoderm lining the laryngotracheal tube, distal to the larynx, differentiates into the epithelium and glands of the trachea and the pulmonary epithelium.
- Cartilage, connective tissue, and muscles of the trachea are derived from the surrounding splanchnic mesenchyme.
Development of the Trachea
- The endoderm forms the epithelium and glands of the trachea.
- The surrounding mesenchyme forms the connective tissue, muscle, and cartilage.
Development of the Larynx
- The epithelium lining the larynx is endodermal in origin.
- The larynx's cartilages and muscles arise from the fourth and sixth pharyngeal arches' mesenchyme.
Development of Bronchi and Lungs
- The respiratory bud develops at the caudal end of the laryngotracheal diverticulum in the fourth week.
- The bud divides into two outpouchings (primary bronchial buds), which grow laterally into the pericardioperitoneal canals (primordia of the pleural cavities).
- Secondary and tertiary bronchial buds develop.
- The lungs acquire a visceral pleura from the splanchnic mesoderm and a parietal pleura from the somatic mesoderm.
Development of Respiratory Passages
- The respiratory passages appear as an endodermal bud arising from the caudal end of the laryngotracheal groove.
- The bud becomes covered by mesenchyme that differentiates into blood vessels, cartilage, smooth muscle, and connective tissue.
- The endoderm lines the entire respiratory tract.
- The lung bud grows caudally and undergoes successive divisions that form the main bronchi.
- Subsequent divisions result in finer branches, culminating in small expansions called infundibula, which become definitive alveoli.
Successive Stages of Bronchial Bud Development
- Diagrams illustrate the development of bronchial buds, bronchi, and lungs from 28 days to 56 days.
- The primordia of secondary bronchial buds and main bronchi are shown at various stages.
- Diagrams show lobes of the lungs in different phases.
Maturation of the Lungs
- The lung development goes through three phases: pseudoglandular, canalicular, and terminal sac.
- The repeated divisions of the endodermal tubes create a glandular appearance in the lung.
- Nuclei are variable, and mitosis is common in the earliest stages.
- Epithelial cells are separated from the mesenchyme by a basement membrane.
- Cells become cuboidal, and cilia and goblet cells appear. Clara cells differentiate, and endocrine cells can be found later.
Canalicular Phase
- The canalicular phase extends from week 17 to 26.
- Tubules transform into canaliculi, with epithelial flattening and cytodifferentiation.
- Osmiophilic lamellar bodies associated with surfactant production appear.
- The cells have well-developed endoplasmic reticulum and ribosomes.
- Type II pneumocytes and surfactant appear.
- Intercellular junctions shift to the lower cell half.
Terminal Sac Phase
- The terminal sac phase extends from week 26 until birth.
- Respiratory bronchioles develop into tubes with flattened epithelium on one side and ciliated cuboidal epithelium on the other.
- Clusters of five to six generations of saccules appear and are lined with flattened epithelium associated with capillaries.
- Alveoli are small and shallow at birth, with only a few present in respiratory bronchioles.
- Inflation of alveoli begins after birth, first in the hilar region.
- Distal alveoli are inflated after several hours of breathing.
- The adult number of alveoli is reached by the eighth postnatal year.
Adaptations for Autonomous Gas Exchange
- Surfactant production in alveolar sacs.
- Transformation of lungs from secretory to gas-exchanging organs
- Parallel pulmonary and systemic circulations.
Histological Stages
- Images show the histological stages (pseudoglandular, canalicular, etc.) of lung development at different weeks of gestation.
- Stages include the appearance of bronchi, bronchioles, and alveoli, along with changes in the epithelial cells and surrounding tissue.
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Description
Explore the stages of respiratory system development in this quiz. Learn about the formation of the lower respiratory organs and the laryngotracheal diverticulum, crucial for proper lung function. Test your knowledge on embryonic development and the formation of key structures.
