Histology/Embryology – Respiratory Development

1. Which of the following series of stages are in the correct developmental sequence?

Alveolar period, terminal saccular period, canalicular period, pseudoglandular period

Pseudoglandular period, terminal saccular period, canalicular period, alveolar period

Terminal saccular period, pseudoglandular period, alveolar period, canalicular period

Pseudoglandular period, canalicular period, terminal saccular period, alveolar period

Canlicular period, alveolar period, terminal saccular period, pseudoglandular period

The correct developmental sequence of the stages is as follows: pseudoglandular period, canalicular period, terminal saccular period, alveolar period. During the pseudoglandular period, the lung buds develop and divide into bronchial tree structures. This is followed by the canalicular period, where the lungs continue to develop and the respiratory bronchioles form. The terminal saccular period comes next, during which the terminal sacs and alveoli begin to form. Finally, in the alveolar period, the number and size of the alveoli increase, allowing for gas exchange to occur.

Explanation

The correct developmental sequence of the stages is as follows: pseudoglandular period, canalicular period, terminal saccular period, alveolar period. During the pseudoglandular period, the lung buds develop and divide into bronchial tree structures. This is followed by the canalicular period, where the lungs continue to develop and the respiratory bronchioles form. The terminal saccular period comes next, during which the terminal sacs and alveoli begin to form. Finally, in the alveolar period, the number and size of the alveoli increase, allowing for gas exchange to occur.

2. A young mother brings her recently born infant into your office and complains that the infant gags and chokes after swallowing milk. A physical examination indicates excessive mucus around the mouth and nose, abdominal distention, pneumonitis, and radiographs indicate air in the infant's stomach. Which is the most likely cause?

Hypertrophic pyloric stenosis

Tracheoesophageal fistula

Congenital lobar emphysema

Respiratory distress syndrome

Pulmonary hypoplasia

The most likely cause for the infant's symptoms is a tracheoesophageal fistula. This condition is characterized by an abnormal connection between the esophagus and the trachea, leading to the passage of air and fluids between the two structures. The symptoms of gagging, choking, excessive mucus, abdominal distention, and pneumonitis are all consistent with this condition. The presence of air in the infant's stomach on radiographs further supports the diagnosis of a tracheoesophageal fistula.

Explanation

The most likely cause for the infant's symptoms is a tracheoesophageal fistula. This condition is characterized by an abnormal connection between the esophagus and the trachea, leading to the passage of air and fluids between the two structures. The symptoms of gagging, choking, excessive mucus, abdominal distention, and pneumonitis are all consistent with this condition. The presence of air in the infant's stomach on radiographs further supports the diagnosis of a tracheoesophageal fistula.

3. Which of the following statements concerning the developing respiratory system is correct?

The blood-air barrier develops during the alveolar period

A premature infant born at the end of the pseudoglandular period will survive if given intensive care

The lungs of a newborn baby contain the same number of alveoli as an adult

Pseudostratified columnar epithelium of the respiratory system is derived from splanchnic mesoderm

Respiratory bronchioles develop during the canalicular period

During the canalicular period, the respiratory bronchioles develop. This period occurs between the pseudoglandular period and the alveolar period in the development of the respiratory system. The respiratory bronchioles are the smallest airways in the lungs and are responsible for conducting air to the alveoli. Therefore, this statement correctly describes the development of the respiratory system.

Explanation

During the canalicular period, the respiratory bronchioles develop. This period occurs between the pseudoglandular period and the alveolar period in the development of the respiratory system. The respiratory bronchioles are the smallest airways in the lungs and are responsible for conducting air to the alveoli. Therefore, this statement correctly describes the development of the respiratory system.

4. A premature female infant is born about 24 weeks after fertilization and develops rapid, labored breathing shortly after birth. She is immediately transferred to intensive care where she is diagnosed with hyaline membrane disease (HMD). Which of the following is most likely deficient in the infant?

Alveolar ducts

Lung surfactant

Terminal saccules

Type 1 alveolar cells

Type 2 alveolar cells

(RDS) of the newborn is an acute lung disease caused by surfactant deficiency.

Explanation

(RDS) of the newborn is an acute lung disease caused by surfactant deficiency.

5. In which stage of lung maturation is the blood-air barrier established?

Embryonic period

Pseudoglandular period

Canalicular period

Terminal sac period

Alveolar period

During the terminal sac period, which occurs between weeks 24 and 36 of gestation, the blood-air barrier is established in the lungs. This is when the terminal sacs, which are the precursors to the alveoli, begin to form and differentiate. The thin walls of the terminal sacs allow for gas exchange between the air in the lungs and the blood vessels surrounding them, thus establishing the blood-air barrier. This stage is crucial for the maturation of the lungs and prepares them for breathing after birth.

Explanation

During the terminal sac period, which occurs between weeks 24 and 36 of gestation, the blood-air barrier is established in the lungs. This is when the terminal sacs, which are the precursors to the alveoli, begin to form and differentiate. The thin walls of the terminal sacs allow for gas exchange between the air in the lungs and the blood vessels surrounding them, thus establishing the blood-air barrier. This stage is crucial for the maturation of the lungs and prepares them for breathing after birth.

6. What is the function of the ductus venosus?

To participate in the formation of the inferior vena cava

To allow blood to bypass the hepatic sinusoids

To connect the right umbilical vein to the superior vena cava

To assist in blood flow to the hepatic sinusoids

To form a conduit through the diaphragm

In the fetus, the ductus venosus shunts a significant majority (80%) of the blood flow of the umbilical vein directly to the inferior vena cava. Thus, it allows oxygenated blood from the placenta to bypass the liver

Explanation

In the fetus, the ductus venosus shunts a significant majority (80%) of the blood flow of the umbilical vein directly to the inferior vena cava. Thus, it allows oxygenated blood from the placenta to bypass the liver

7. The chart below shows the four stages of lung maturation with the events occurring at each stage. Which of these lists is CORRECT?

	Stage	Weeks	Respiration	Process
A	Pseudoglandular	6-16	Yes	More terminal saccules, blood-air barrier, and type I and II pneumocytes form
B	Canalicular	16-26	Only towards the end	Respiratory bronchioles, alveolar ducts and some terminal saccules form
C	Terminal saccular	26-birth	Yes	Terminal bronchioles form
D	Alveolar	Birth – 8 years	No	Increased respiratory bronchioles, terminal saccules and mature alveoli

A

B

C

D

The correct answer is B because during the Canalicular stage, which occurs between 16-26 weeks, respiratory bronchioles, alveolar ducts, and some terminal saccules form. This is different from the other stages where different structures form. In stage A, the Pseudoglandular stage, more terminal saccules, blood-air barrier, and type I and II pneumocytes form. In stage C, the Terminal saccular stage, terminal bronchioles form. In stage D, the Alveolar stage, there is an increase in respiratory bronchioles, terminal saccules, and mature alveoli.

Explanation

The correct answer is B because during the Canalicular stage, which occurs between 16-26 weeks, respiratory bronchioles, alveolar ducts, and some terminal saccules form. This is different from the other stages where different structures form. In stage A, the Pseudoglandular stage, more terminal saccules, blood-air barrier, and type I and II pneumocytes form. In stage C, the Terminal saccular stage, terminal bronchioles form. In stage D, the Alveolar stage, there is an increase in respiratory bronchioles, terminal saccules, and mature alveoli.

8. At which of the following locations does fetal blood contain the highest level of oxygen?

Left umbilical artery

Proximal region of descending aorta

Ductus venosus

Right atrium

Inferior vena cava

The correct answer is ductus venosus. The ductus venosus is a blood vessel that connects the umbilical vein to the inferior vena cava in the developing fetus. It allows oxygenated blood from the placenta to bypass the liver and flow directly to the heart. As a result, the blood in the ductus venosus has the highest level of oxygen compared to the other locations listed.

Explanation

The correct answer is ductus venosus. The ductus venosus is a blood vessel that connects the umbilical vein to the inferior vena cava in the developing fetus. It allows oxygenated blood from the placenta to bypass the liver and flow directly to the heart. As a result, the blood in the ductus venosus has the highest level of oxygen compared to the other locations listed.

9. A 2 hour old term newborn male has coughing, choking, and cyanosis prior to feeding. A nasogastric tube is placed and meets resistance at 10cm. Prenatal history is significant for polyhydramnios. Which of the following is most likely to be found in this infant?

Vertebral defects

Anal atresia

Congenital heart defects

Tracheoesophageal fistula

Esophageal atresia

The presence of coughing, choking, and cyanosis prior to feeding, along with resistance encountered at 10cm during nasogastric tube placement, suggests a possible obstruction in the esophagus. Given the prenatal history of polyhydramnios, which is often associated with esophageal atresia, it is likely that this newborn has esophageal atresia. Esophageal atresia is a condition where the esophagus does not fully develop, leading to an incomplete connection between the mouth and stomach. This results in feeding difficulties and respiratory distress, which explains the symptoms seen in this newborn.

Explanation

The presence of coughing, choking, and cyanosis prior to feeding, along with resistance encountered at 10cm during nasogastric tube placement, suggests a possible obstruction in the esophagus. Given the prenatal history of polyhydramnios, which is often associated with esophageal atresia, it is likely that this newborn has esophageal atresia. Esophageal atresia is a condition where the esophagus does not fully develop, leading to an incomplete connection between the mouth and stomach. This results in feeding difficulties and respiratory distress, which explains the symptoms seen in this newborn.

10. A newborn infant suffers from a posterolateral defect on the left side of the body. His abdominal contents have herniated through the defect into the thoracic cavity, and as a result, the infant suffers from pulmonary hypoplasia. His breathing difficulty is life threatening because the herniation has inhibited lung development and inflation. This congenital defect is due to a malformation of which of the following?

Mesentery of the esophagus

Muscular ingrowth of the body wall

Pleuropericardial membrane

Pleuroperitoneal membrane

Septum transversum

The correct answer is the pleuroperitoneal membrane. In this case, the newborn infant has a defect in the pleuroperitoneal membrane on the left side of the body. This defect allows the abdominal contents to herniate into the thoracic cavity, leading to pulmonary hypoplasia. The pleuroperitoneal membrane normally separates the thoracic and abdominal cavities, and when it is malformed, it can result in this type of congenital defect.

Explanation

The correct answer is the pleuroperitoneal membrane. In this case, the newborn infant has a defect in the pleuroperitoneal membrane on the left side of the body. This defect allows the abdominal contents to herniate into the thoracic cavity, leading to pulmonary hypoplasia. The pleuroperitoneal membrane normally separates the thoracic and abdominal cavities, and when it is malformed, it can result in this type of congenital defect.