Development of the Respiratory System Flashcards
When does the primordium of the tracheobronchial tree develop?
During week 4
What starts as a median laryngotracheal groove in the caudoventral wall of the primitive pharynx?
Primordium of tracheobronchial tree
What gives rise to the epithelium and glands of the larynx, trachea, bronchi, and the pulmonary epithelium?
The endoderm lining of the median laryngotracheal groove
Connective tissue, cartilage, and smooth muscle of the larynx, trachea, and bronchi develop from what?
Splanchnic mesenchyme surrounding the foregut
The laryngotracheal groove deepens into what?
A respiratory diverticulum ventrally
The respiratory diverticulum enlarges distally into what?
A lung bud
Where does the epithelial lining of the larynx develop from?
The endoderm of the cranial end of the laryngotracheal tube
The cartilages of the larynx develop from where?
The cartilages in the 4th and 6th pairs of pharyngeal arches
The laryngeal cartilages develop from where?
Mesenchyme that is derived from neural crest cells
The mesenchyme at the cranial end of the laryngotracheal tube proliferates rapidly, producing what?
Paired arytenoid swellings
The paired arytenoid swellings grow toward the tongue, converting the slitlike aperture, “the primordial glottis”, into what?
A T-shaped laryngeal inlet
The laryngeal epithelium proliferates rapidly, resulting in?
Temporary occlusion of the laryngeal lumen
Recanalization of the larynx normally occurs by when?
The 10th week
Vocal cords develop from?
Folds of mucous membrane during the process of recanalization
The epiglottis develops from?
The caudal part of the hypo pharyngeal eminence
What is laryngeal atresia?
Rare anomaly resulting from failure of recanalization of the larynx, and causes obstruction of the upper fetal airway. AKA congenital high airway obstruction syndrome
Laryngeal web results from?
Incomplete recanalization of the larynx causing partial airway obstruction
The endodermal lining of the laryngotracheal tube distal to the larynx differentiates into?
The epithelium and glands of the trachea and the pulmonary epithelium
The cartilage, connective tissue, and muscles of the trachea are derived from?
The splanchnic mesenchyme surrounding the laryngotracheal tube
A tracheoesophageal fistula is an abnormal communication between the trachea and esophagus caused by?
A malformation of the tracheoesophageal septum
Tracheoesophageal fistula is generally associated with?
Esophageal atresia (a condition in which a body orifice or passage in the body is abnormally closed or absent) Polyhydramnious (too much amniotic fluid in the amniotic sac)
Tracheoespophageal fistula results in?
Gaging and cyanosis after feeding, excessive accumulation of saliva or mucus in the nose and mouth, abdominal distention after crying, and reflux of gastric contents into lungs causing pneumonitis
Tracheoesophageal fistula is most commonly located where?
Between the esophagus and distal third of the trachea
The lung bud develops into what?
2 endodermal bronchial buds
The 2 endodermal bronchial buds grow into what?
Pericardioperitoneal cavities and the primordial of the pleural cavities
When do the bronchial buds enlarge into the primordial of a primary bronchus?
Early in week 5
Which bronchial bud is slightly larger and is oriented more vertically?
The right bronchial bud
The primary bronchi subsequently divides into what by week 7?
Secondary bronchi and then into tertiary bronchi
What happens to the primary bronchi by week 24?
They divide another 14 times and respiratory bronchioles have developed
Before birth, the bronchi will divide then another how many times before birth?
7 more times before birth
As the bronchi develop, the surrounding mesenchyme synthesizes what?
The surrounding cartilages, smooth muscle, connective tissue, and capillaries
The lungs acquire a layer of visceral pleura from where?
The splanchnic mesenchyme
The splanchnic layer forms what?
The circulatory system and future gut wall
The thoracic body wall becomes lined by what?
A layer of parietal pleura derived from the somatic mesoderm
Maturation of the lungs is divided into what 4 periods?
- Pseudo glandular period
- Canalicular period
- Terminal saccular period
- Alveolar period
Pseudo Glandular Period/Stage
Weeks 5-17
- Respiration is not possible
- Premature fetuses cannot survive
- Lungs look like an exocrine organ
Canalicular Period/Stage
Weeks 13-25
- Overlaps with pseudo glandular period because cranial segments of the lungs mature faster than caudal ones
- The lumen of the bronchi and terminal bronchioles become larger and the lungs become vascularized
- Respiration is not possible
- Premature rarely survive
Terminal Sac Period/Stage
Weeks 24-birth
- Type 1 & Type 2 pneumocytes are present
- The epithelium becomes very thin
- The intimate contact between epithelial and endothelial cells establishes the blood-air barrier
- Respiration is possible
- Premature fetuses born between weeks 25-28 can survive with intensive care
Alveolar Period/Stage
Birth-8 years old
- 95% of the mature alveoli develop after birth
- Respiratory bronchioles, terminal sacs, alveolar ducts, and alveoli increase in number
- Chest radiograph is more dense in children
The blood-air barrier permits what?
Adequate gas exchange for survival of the fetus if it is born prematurely
When does the production of surfactant increase?
During the last 2 weeks of pregnancy
Type II pneumocytes secrete what?
Surfactant counteracting the surface tension forces and facilitating expansions of the terminal sacs
Adequate pulmonary vasculature and sufficient surfactant are critical for what?
The survival of premature infants
Developing lungs at birth are half filled with amniotic fluid. How is the fluid in the lungs cleared?
- through the mouth and nose by pressure on the thorax during delivery
- into the pulmonary capillaries
- into the lymphatics and pulmonary arteries and veins
What 3 factors are important for normal lung development?
- Adequate thoracic space for lung growth
- Fetal breathing movements
- Adequate amniotic fluid volume
