1. Development of The Lower Respiratory System: Larynx And Trachea
LUFUKUJA G.

2. Development of the Larynx
The larynx develops from the entodermal lining of the cranial end of the laryngotracheal tube and surrounding mesenchyme (from branchial arches IV, V and VI)
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3. Development of the Larynx…
THE MESENCHYME of the two arches proliferates to produce paired arytenoid swellings, giving the primitive glottis a T-shaped appearance and reducing the laryngeal lumen to a slit. The laryngeal cartilages develop within the arytenoid swellings from the cartilage bars of the branchial arches.
LUFUKUJA G.

4. Development of the Larynx…
The epiglottis develops from the caudal half of the hyopbranchial eminence, a derivative of branchial arches III and IV
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6. Larynx…
THE ENTRANCE TO THE LARYNX ends blindly, between weeks 7 to 10, because of the fusion of epithelium. The laryngeal epithelium proliferates rapidly, resulting in a temporary occlusion of the lumen.
LUFUKUJA G.

7. The laryngeal epithelium proliferates rapidly, resulting in a temporary occlusion of the lumen.
LUFUKUJA G.

8. Development of the Larynx…
The epithelium breaks down, the laryngeal aditus enlarges and recanalizes. Recanalization of the larynx occur by 10th week.
A pair of lateral recesses, the laryngeal ventricles, form which are bound cranially and caudally by anteroposterior folds of mucous membrane, the future vestibular (false) and vocal (true) folds, respectively
The laryngeal muscles develop from muscle elements in branchial arches IV to VI and are innervated by laryngeal branches of the vagus nerve
LUFUKUJA G.

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10. Development of the Larynx…
Subsequently, vacuolization and recanalization produces a pair of lateral recesses, the laryngeal ventricles that are bounded by folds of tissue that differentiate into the false and true vocal cords.
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13. Embryological anomalies Laryngeal atresia
Laryngeal atresia is a congenital failure of the laryngeal opening to develop, resulting in partial or total obstruction at or just above or below the glottis. Failure of recanalization of the laryngotracheal tube during the third month of gestation leads to laryngeal atresia.
LUFUKUJA G.

14. Laryngotracheal stenosis
Laryngotracheal stenosis (LS), a narrowing of the larynx and/or trachea, is a condition that can occur in infants and children for several reasons. Acquired LS develops as a result of trauma to the larynx and trachea, usually from endotracheal intubation, while congenital LS is a narrowing present at birth. Neck trauma, inhalation burns, and prolonged intubation can also lead to LS.
Symptoms :Stridor (noisy breathing); Feeding problems; Croup, a loud cough that sounds like barking
Treatment: This condition may require surgical correction if severe. 
LUFUKUJA G.

15. Development of the trachea
The trachea: the entodermal lining of the middle segment of the laryngotracheal tube forms the epithelium and glands of the trachea. Mesenchymal cells (from splanchnic mesenchyme) surround the tracheal tube and ultimately form the cartilage, connective tissue, and smooth muscles of its walls
BY WEEK 8: mesenchymal rudiments of the tracheal cartilages are seen and, in the following 2 weeks, the masses form cartilage beginning cranially and extending caudally. Simultaneously, fibroelastic tissue of the tracheal wall arises from mesenchyme between the cartilage and, posteriorly, between the ends of the embryonic rings smooth muscle (the trachealis) arises
LUFUKUJA G.

16. Development of the trachea…
By week 12, mucosal glands are seen and develop in a craniocaudal direction
By the end of week 20, all major microscopic features of the trachea are visible, but it is short and narrow while the larynx is relatively long This relationship remains until after birth when the trachea outgrows the larynx to reach its final form
LUFUKUJA G.

17. Development of the bronchi
In the week 5 of development, the endodermal lung bud, surrounded by splanchnic mesenchyme, has developed 2 bronchial buds that will differentiate into the major bronchi as well as their ramifications in the lungs. Each bud enlarges to form a primitive primary bronchus with the right being slightly larger and more vertical than the left
LUFUKUJA G.

18. Development of the bronchi…
EACH PRIMARY BRONCHUS grows laterally into the medial walls of the pericardioperitoneal canals or primitive pleural cavities. Simultaneously, the right primary bud gives rise to 2 secondary buds (bronchi), whereas the left only gives rise to one. Thus, in the adult, there are 3 secondary bronchi and lobes (superior, middle, and inferior) on the right, but only 2 secondary bronchi and lobes on the left (superior and inferior)
LUFUKUJA G.

19. Development of the bronchi…
LUFUKUJA G.

20. Development of the bronchi…
EACH SECONDARY LUNG BUD then undergoes progressive dichotomous branching to form tertiary (segmental) bronchi: 10 in the right lung and 8 or 9 in the left, which begin to appear by week 7 Each tertiary bronchus with its surrounding mass of mesenchyme will eventually form a bronchopulmonary segment
LUFUKUJA G.

21. Development of the Pulmonary vessels
Pulmonary vessels EARLY IN WEEK 4, a primitive pulmonary artery arises from the ventral aspect of both right and left sixth (pulmonary) aortic arches and extends caudally toward the developing tubular lung bud, eventually being incorporated into the mesenchymal tissue around the primitive trachea and bronchial buds
THE VENOUS RETURN develops from the mesenchyme and the heart wall and, instead of following the bronchial tree, runs between bronchopulmonary segments
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24. Maturation of the Lungs
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25. Maturation of the Lungs…
The lungs can be described as undergoing 4 phases of development.
Pseudoglandular stage (6-16 weeks)
Canalicular stage (16-26 weeks)
Terminal sac phase (26 to birth)
Alveolar stage (up to ten years)
LUFUKUJA G.

26. Maturation of the Lungs…
LUFUKUJA G.

27. Pseudoglandular phase (6-16 weeks)
Branching has continued to form terminal bronchioles. No respiratory bronchioles or alveoli are present
Developing lungs somewhat resembles an exocrine gland during this period
Respiration is not possible thus Fetuses born during this period cannot survive
LUFUKUJA G.

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29. Canalicular Period(16-26 weeks)
Each terminal bronchiole divides into 2 or more respiratory bronchioles, which in turn divide into 3-6 alveolar ducts. The cuboidal cells lining the respiratory bronchioles. Lumina of bronchi become larger, and the lung tissue becomes highly vascularized
Respiration is possible toward the very end of this phase because a few of the terminal alveolar sacs (primordial alveoli) located superiorly have developed at the ends of the respiratory bronchioles.
Fetus born at the end of this period may survive
LUFUKUJA G.

30. Canalicular Period(16-26 weeks)…
LUFUKUJA G.

31. Terminal Sac Period (26 weeks to birth)
Cuboidal cells become very thin and flat and intimately associated with blood and lymph capillaries. Terminal sacs (primitive alveoli) form
Gas exchange occurs across type I pneumocytes
Scattered among the squamous epithelial cells are rounded secretory epithelial cells, type II pneumocytes that secrete a mixture of phospholipids called surfactant
Surfactant reduces surface tension and facilitates expansion of the terminal saccules
LUFUKUJA G.

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33. Terminal Sac Period (26 weeks to birth)…
Surfactant production increases during the terminal stages of pregnancy. Fetuses born prematurely at weeks may survive if given intensive care
Fetuses may suffer from respiratory distress due to surfactant deficiency
LUFUKUJA G.

34. Alveoli Period (8 months to childhood)
Mature alveoli have well-developed epithelial endothelial (capillary) contacts.
The number of respiratory bronchioles and alveoli increase steadily with the alveoli having more intimate contact with the epithelium of the capillaries.
Monday, April 08, 2019

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36. Alveoli Period (8 months to childhood)
Fetal Breathing movements begin before birth and cause aspiration of amniotic fluid that stimulate lung development and conditioning of respiratory muscles
At birth Lung fluid is reabsorb but not the surfactant coat. The surfactant prevents the collapse of the alveoli during expiration.
Growth of the lungs after birth is due to an increase in the number of respiratory bronchioles and alveoli and not an increase in size.
Monday, April 08, 2019

37. Respiratory distress syndrome (RDS)
Surfactant is particularly important for survival of the premature infant. When surfactant is insufficient, the air-water (blood) surface membrane tension becomes high, bringing great risk that alveoli will collapse during expiration. As a result, respiratory distress syndrome (RDS) develops.
This is a common cause of death in the premature infant. In these cases the partially collapsed alveoli contain a fluid with a high protein content, many hyaline membranes, and lamellar bodies, probably derived from the surfactant layer.
LUFUKUJA G.

38. Oligohydraminios
Oligohydramnios is a condition in pregnancy characterized by a deficiency of amniotic fluid. It is the opposite of polyhydramnios.
When oligohydromnios is severely and chronic because of amniotic fluid leakage, lung development is retarded and severe pulmonary hypoplasia results from the restriction of the fetal thorax. Approximately 50% of the time, fetal renal system abnormalities cause severe oligohydramnios
LUFUKUJA G.

39. Oligohydraminios…
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41. Development of the Diaphragm
LUFUKUJA G.

42. The diaphragm develops from four embryonic components:
Septum transversum
Pleuroperitoneal membranes
Dorsal mesentery of esophagus, in which the crura of the diaphragm develop
Muscular in growth from lateral body walls
LUFUKUJA G.

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44. Septum transversum
The septum is derived from visceral (splanchnic) mesoderm surrounding the heart and assumes its position between the primitive thoracic and abdominal cavities when the cranial end of the embryo grows and curves into the fetal position
LUFUKUJA G.

45. Septum transversum
This septum does not separate the thoracic and abdominal cavities completely, but leaves large openings, the pericardioperitoneal canals, on each side of the foregut
LUFUKUJA G.

46. Septum transversum…
Although the pleural cavities are separate from the pericardial cavity, they remain in open communication with the abdominal (peritoneal) cavity by way of the pericardioperitoneal canals.
During further development, the opening between the prospective pleural and peritoneal cavities is closed by crescent-shaped folds, the pleuroperitoneal folds, which project into the caudal end of the pericardioperitoneal canals
LUFUKUJA G.

47. Septum transversum…
Gradually, the folds extend medially and ventrally, so that by the seventh week, they fuse with the mesentery of the esophagus and with the septum transversum. Hence, the connection between the pleural and peritoneal portions of the body cavity is closed by the pleuroperitoneal membranes.
Further expansion of the pleural cavities relative to mesenchyme of the body wall adds a peripheral rim to the pleuroperitoneal membranes. Once this rim is established, myoblasts originating from somites at cervical segments three to five (C3–5) penetrate the membranes to form the muscular part of the diaphragm.
LUFUKUJA G.

48. Septum transversum…
During the fourth week, the septum transversum lies opposite cervical somites, and nerve components of the third, fourth, and fifth cervical segments of the spinal cord grow into the septum. At first, the nerves, known as phrenic nerves, pass into the septum through the pleuropericardial folds. This explains why further expansion of the lungs and descent of the septum shift the phrenic nerves that innervate the diaphragm into the fibrous pericardium.
LUFUKUJA G.

49. Septum transversum…
The phrenic nerves supply the diaphragm with its motor and sensory innervation. Since the most peripheral part of the diaphragm is derived from mesenchyme of the thoracic wall, it is generally accepted that some of the lower intercostal (thoracic) nerves contribute sensory fibers to the peripheral part of the diaphragm.
LUFUKUJA G.

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51. Embryological anomalies
Congenital hiatal hernia: because of large esophageal hiatus
LUFUKUJA G.

52. Embryological anomalies
LUFUKUJA G.

53. Embryological anomalies
LUFUKUJA G.

54. Embryological anomalies
A severe left-sided congenital diaphragmatic hernia with liver and bowel herniation in to the fetal chest.
Commonly through a posterolateral defect in diaphragm. Mostly on left side. Left lung shows hypoplasia
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