L24. Embryology - Lung Development

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Questions and Answers

What condition is primarily caused by esophageal atresia in neonates?

Oligohydramnios

Pulmonary hypoplasia

Polyhydramnios (correct)

Congenital diaphragmatic hernia

What is the most common cause of congenital diaphragmatic hernias in newborns?

Shortening of the diaphragm muscle

Failure of the pleuroperitoneal membranes to close (correct)

Underdevelopment of the esophagus

Presence of a peritoneal sac

In congenital diaphragmatic hernias, where are the abdominal viscera typically found?

In the pleural cavity (correct)

In the heart's pericardial sac

In the mediastinum

In the abdominal cavity

What is a potential consequence of failure of the pericardioperitoneal canal to close?

Esophageal hernia Signup and view all the answers

Which of the following describes a parasternal hernia?

Small intestine entering the mediastinum region Signup and view all the answers

What primary germ layer gives rise to the internal lining of the larynx?

Endoderm Signup and view all the answers

Which components of the larynx are formed from mesenchyme?

Thyroid, cricoid, and arytenoid cartilages Signup and view all the answers

At what gestational week does the laryngotracheal opening begin to take shape?

Week 4 Signup and view all the answers

What is the process called that leads to the reopening of the laryngeal cavity?

Recanalization Signup and view all the answers

Which pharyngeal arch is responsible for sensory and motor innervation above the vocal folds?

4th pharyngeal arch Signup and view all the answers

Which nerves provide innervation to the laryngeal muscles and mucosa below the vocal folds?

Recurrent laryngeal nerves Signup and view all the answers

What structure is formed from the mesenchyme between the 4th and 6th pharyngeal arches?

Laryngeal cartilages Signup and view all the answers

At what point during development is the epiglottis formed?

Between the 3rd and 4th pharyngeal arches Signup and view all the answers

What are the paired ventricles of the larynx formed from?

Reopening of the occluded laryngeal cavity Signup and view all the answers

Which cartilages complete their growth by the 12th week of gestation?

Thyroid, cricoid, and arytenoid cartilages Signup and view all the answers

What significant change occurs in the type II respiratory epithelial cells by week 26?

They start releasing surfactant into the lumen. Signup and view all the answers

Why is funding must be available to facilitate survival for premature births by week 26?

Functional blood/gas exchange can occur. Signup and view all the answers

At which gestational week is adequate blood-gas exchange possible for premature infants?

Week 26 Signup and view all the answers

What is the primary function of surfactant in the lungs?

Lower tension at the air-alveolar interface. Signup and view all the answers

What occurs during the canalicular period of lung development?

No gas exchange is possible. Signup and view all the answers

How many generations of subdivisions does the respiratory tree undergo by the sixth month of gestation?

17 generations Signup and view all the answers

What marks the terminal sac stage of lung development?

Formation of primordial terminal sacs. Signup and view all the answers

What occurs after the alveolar stage of lung development in early childhood?

Formation of additional alveolar tree subdivisions. Signup and view all the answers

What is a key developmental milestone reached by the end of week 26 concerning gas exchange?

Initiation of functional blood/gas exchange. Signup and view all the answers

What developmental period is characterized by the formation of the conducting system of the bronchial tree?

Pseudoglandular period Signup and view all the answers

During which period do terminal bronchioles start dividing into respiratory bronchioles?

Canalicular period Signup and view all the answers

What is the primary feature of the terminal sac stage in terms of cellular structure?

Single layer of flattened epithelial cells Signup and view all the answers

Why is survival from premature birth not possible during the pseudoglandular period?

Gas exchange structures have not developed Signup and view all the answers

What characterizes the ducts formed during the canalicular period?

Cuboidal epithelium surrounded by smooth muscle Signup and view all the answers

At what stage are primitive terminal sacs first formed?

Weeks 24-birth Signup and view all the answers

What is the main challenge for premature infants born during the canalicular stage?

Insufficient gas exchange capabilities Signup and view all the answers

What developmental structure emerges from terminal bronchioles during the canalicular period?

Respiratory bronchioles Signup and view all the answers

Which of the following statements about the terminal sac stage is false?

Surfactant production is fully operational. Signup and view all the answers

What defines the epithelial lining of the respiratory bronchioles formed during weeks 16-24?

Cuboidal epithelium Signup and view all the answers

What is the primary role of type II alveolar epithelial cells during lung development?

Activation and migration of alveolar macrophages Signup and view all the answers

What key development occurs during the canalicular period in lung formation?

Formation of terminal and respiratory bronchioles Signup and view all the answers

What anatomical structure is primarily responsible for separating the pleural and pericardial cavities?

Pleuropericardial folds Signup and view all the answers

Which condition involves a lack of communication between the esophagus and trachea during development?

Esophageal atresia Signup and view all the answers

What contributes to the muscular part of the diaphragm during development?

Invasion of myoblasts Signup and view all the answers

What is a consequence of full esophageal atresia in fetal development?

Polyhydramnios Signup and view all the answers

Which anatomical structure's development is essential for the compartmentalization of the pleural and peritoneal cavities?

Pleuroperitoneal folds Signup and view all the answers

During lung maturation, what is the final developmental period called?

Alveolar period Signup and view all the answers

Study Notes

Lung Development Stages

Pseudoglandular Period (Weeks 5-16): Formation of the conducting system of the bronchial tree.
Canalicular Period (Weeks 16-24): Formation of the duct system for gas exchange.
- Terminal bronchioles divide into respiratory bronchioles.
- Cuboidal epithelium with smooth muscle and no cartilage.
- Rapidly forming capillary beds in surrounding mesenchyme.
- Premature birth survival unlikely due to no gas exchange.
Terminal Sac Stage (Weeks 24-Birth): Formation of primitive terminal sacs (primordial alveolar sacs) off respiratory bronchioles.
- Single layer of flattened epithelial cells close to capillaries in mesoderm.
- Limited gas/blood exchange possible.
- Type II cells release surfactant by week 26, which supports premature birth survival.
- By week 26, sufficient alveolar sacs for adequate blood-gas exchange.
- 17 generations of subdivisions by the sixth month.
- 6 more subdivisions post-natally.
Alveolar Stage (Late Gestation-Early Childhood): Maturation of the lungs.
- Alveoli expand and mature, increasing surface area for gas exchange.

Role of Breathing Movements in Lung Development

Breathing movements expand the lungs, stimulating further development.
This promotes formation of new airways, alveolar sacs, and capillaries.
Essential for normal lung function.

Role of Type II Alveolar Epithelial Cells

Produce surfactant, which reduces surface tension in the alveoli.
Prevents alveolar collapse during exhalation.
Critical for gas exchange and lung function.

Summary of Lung Maturation

Lungs are not fully mature at birth, with continued development into early childhood.
Premature birth before 26 weeks poses significant risks due to immature lungs.

Transition of Developing Lungs into the Pleural Cavity

Early development within the splanchnic mesoderm.
Expansion into the pericardioperitoneal canals and acquisition of visceral pleura.
Mesothelial lining of the pleural cavity.

Formation of the Pericardial and Pleural Cavities

Pleuropericardial Folds (Membranes):
- Contain cranial and caudal folds.
- Closure of the right and left pleuropericardial folds separates the pleural and pericardial cavities.

Formation of the Thoracic Diaphragm and Compartmentalization of the Pleural and Peritoneal cavities

Septum Transversum: Forms the central tendon of the diaphragm.
Pleuroperitoneal Folds (Membranes): Grow ventrally and meet the septum transversum, separating the pleural and peritoneal cavities.
Myoblast Migration: Contributes to the muscular part of the diaphragm.
Displacement of Diaphragm: Moves from the cervical region to the thoracic region.
Innervation:
- Peripheral region of the diaphragm: Motor and sensory innervation from nerves associated with cervical segments.
- Central region of the diaphragm: Motor and sensory innervation from phrenic nerves originating from C3, C4, and C5 spinal segments.

Clinical Significance

Esophageal Atresia with or without Tracheoesophageal Fistulas:
- Atresia: Complete closure of the esophagus.
- Fistula: Abnormal connection between the esophagus and trachea.
- Esophageal Atresia with Tracheoesophageal Fistula: Can result in polyhydramnios, aspiration, and respiratory distress.
- Full Esophageal Atresia: Prevents swallowing and passage of amniotic fluid into the gastrointestinal tract, leading to polyhydramnios.
Diaphragmatic Hernias:
- Congenital: Most frequent cause is failure of one or both pleuroperitoneal membranes to close.
- Parasternal Hernia: Failure of muscle fibers formation near the sternal attachment.
- Esophageal Hernia: Under-development of the esophagus or failure of pericardioperitoneal canal closure.

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Description

Test your knowledge about the stages of lung development, including the Pseudoglandular, Canalicular, and Terminal Sac stages. Understand the structural changes that occur and their implications for gas exchange and premature birth survival. Challenge yourself with questions that cover key concepts and details from this critical developmental period.