Walsh: Perinatal and Pediatric Respiratory Care, 3rd Edition

Chapter 01: Fetal Lung Development 

Answers to Assessment Questions and Clinical Scenarios

1.	B
Rationale: See Table 1-1.
2.	D
Rationale: Lung bud emerges from primordial pharyngeal tissue.
3.	A
Rationale: The tracheobronchial tree emerges in the earliest stage of development. It is frequently compared with a tree growing.
4.	B
Rationale: Type I cells function in gas exchange; type II cells manufacture surfactant, spread it from lamellar bodies through exocytosis, and may also differentiate into type I cells during development.
5.	D
Rationale: Satisfactory gas exchange cannot occur until capillaries have sufficient surface area and are close enough to the airspaces for efficient gas transfer. This development, along with the appearance of surfactant, is therefore critical to the extrauterine survival of the immature fetus. At this point fetal survivability becomes viable during the canalicular stage at 22 to 24 weeks of gestation.
6.	E
Rationale: Fetal lung liquid maintains the structure of the airway lumen and developing alveoli so they are not completely collapsed during development. With fetal breathing movements lung liquid is continuously expelled from the lungs into the oropharynx and is swallowed or excreted into the amniotic fluid.
7.	D
Rationale: Volume increases disproportionately to alveolar number. As body weight doubles in the human infant at 6 months and triples by 1 year, oxygen uptake will increase proportionally; this is matched by an increase in alveolar growth.
8.	B
Rationale: The saccular period was formerly thought to be the last stage of lung development before birth. However, because alveoli form before birth, the termination of this period is now arbitrarily set at 35 to 36 weeks of gestation. At the beginning of this phase, or 26 weeks of gestation, the terminal structures are referred to as saccules and are relatively smooth-walled, cylindrical structures. They then become subdivided by ridges known as secondary crests.
9.	D
Rationale: There are several general causes of pulmonary hypoplasia, including lung tissue compression (e.g., congenital diaphragmatic hernia [CDH]), oligohydramnios, and delayed tissue maturation associated with maternal diabetes.
10.	B.
Rationale: Reid formulated the laws of development of the human lung: (1) the bronchial tree develops by the sixteenth week of intrauterine life; (2) after birth the alveoli develop in increasing number until the age of 8 years and increase in size until growth of the chest wall is finished; and (3) preacinar arteries and veins develop after the airway has been established, and intraacinar vessels develop after the alveoli are generated.