Development Of Respiratory System Flashcards
Which portions of the respiratory tract will develop from the lung bud?
Future trachea and primary bronchi
Describe the origin of the respiratory diverticulum/lung bud
The laryngotracheal groove appears in the floor of the caudal pharynx during week 4. The groove protrudes ventrally, forming an endodermal outgrowth from the foregut, called the lung bud or respiratory diverticulum.
What structure developed to separate the trachea from esophagus?
Tracheoesophageal septum
What is the tracheoesophageal fistula?
An abnormal connection between the trachea and esophagus. It is often associated w another abnormality, esophageal atresia.
How might the most common variation of this fistula result in polyhydramnios?
Polyhydramnios often results from this atresia because the fetus cannot swallow the amniotic fluid as it normally would. Excess fluid can lead to premature rupturing of water and premature delivery.
Name the embryonic germ layer that gives rise to the epithelial lining and glands of the respiratory tract.
Endoderm leads to pulmonary epithelial lining and glands of airways.
Name the embryonic germ layer that gives rise to the smooth muscle and connective tissue of the respiratory tract as well as to the visceral pleura of the lungs
Splanchnic mesoderm
Describe the pattern of branching that arises from the lung bud to eventually give rise to the respiratory tree.
Lung bud-> two primary bronchial buds-> secondary bronchial buds-> tertiary bronchial bud.
Each secondary bronchus will supply a lobe of the lung
What is the respiratory tree order?
Trachea-> primary bronchi-> secondary-> tertiary-> bronchioles-> terminal bronchioles-> respiratory bronchioles-> alveolar ducts-> terminal sacs
Describe the first stage of lung maturation
1) Pseudoglandular Stage (Weeks 6-16)
-lung tissue appears as a collection of exocrine glands
-all major lung structures have developed (except for most distal portions of respiratory tree where gas exchange occurs
-fetus delivered at this stage will not survive
Describe the second phase of lung maturation
2) Canalicular Stage (Weeks 16-26)
-lung tissue becomes highly vascular -respiration is possible at the end of this stage
- each terminal bronchiole has split into 2+ respiratory bronchioles, which have developed primitive alveolar sacs
-fetus born at the end of this stage may survive, but many die due to extremely immature lung development & lack of surfactant
Describe the third phase of lung maturation
3) Terminal Sac Stage (Week 26-Birth)
-more terminal sacs/primitive alveoli develop, establishing blood-air-
barrier
- terminal sac walls consist of a single layer of squamous cells, most of which are Type 1 Alveolar Cells through which gases diffuse
-between the Type 1 Alveolar Cells are a few rounded Type 2 Alveolar Cells, which can divide to replace Type 1 cells, but more importantly, produce, store, and secrete pulmonary surfactant
Describe the fourth phase of lung maturation
4) Alveolar Stage (Weeks 32 - 8 years of age)
-alveoli are fully functional
-95% of mature alveoli develop postnatally (most of which form in the first 3 years) and will continue to develop until age 8
What is the function of pulmonary surfactant And what cells secrete it?
A fatty, phospholipid fluid secreted by Type 2 Alveolar Cells that reduces surface tension at the alveolar interface to prevent alveolar collapse upon exhalation. This is a good thing if you enjoy breathing.
