1. EMBRIOLOGY OF THE RESPIRATORY SYSTEM

2. Formation of Embryonic Disk (first three weeks)
Gastrulation
15 days

3. Formation of Embryonic Disk (first three weeks)
Implantation of blastocyst
Exocoelomic cavity
Inner cell mass
Formation of amniotic cavity inside inner cell mass
Formation of primary yolk sac cavity inside exocoelomic cavity
Formation of bilaminar embryonic disc between amniotic cavity & yolk sac
Epiblast Layer (amniotic cells - epiblasts) – Future Ectoderm
Hypoblast Layer (primary yolk sac cells) – Future Endoderm
Gastrulation:
Formation of primitive streak & groove on surface of Epiblast
Migration of Epiblast cells to Hypoblast & formation of Endoderm
Formation of Intraembryonic Mesoderm between Ectoderm & Endoderm from Epiblast cells
Formation of the Ectoderm from cells remaining in Epiblast
Formation of Trilaminar Enbryonic Disc between amniotic cavity & yolk sac

4. ESTABLISHMENT of GENERAL BODY FORM (at the beginning of the fourth week)
Folding of the flat trilaminar embryonic disk into a cylindrical embryo.
Longitudinal Folding in the Median Plane:
Cranial and caudal folding
Transverse Folding in Horizontal Plane:
Right and left lateral to medial folding.

5. Trilaminar Embryonic Disk (3 weeks)

6. Trilaminar Embryonic Disk (3 weeks)

7. Folding in Median & Horizontal Plane (4th week)

8. Folding in Median & Horizontal Plane (4th week)

9. Oropharyngeal membrane (ruptures at 24 days)

10. Cloacal Membrane (ruptures at the end of 7th week)

11. DEVELOPMENT OF THE FACE (from fourth to eighth weeks)
DEVELOPMENT OF THE PRIMITIVE MOUTH – STOMODEUM (beginning of 4th week)
Rupture of oropharyngeal; membrane (24th day)
DEVELOPMENT OF THE NASAL CAVITY (from the end of 4th week)
Rupture of oronasal membrane (6th week)
Development of paranasal air sinuses from deverticuli of nasal walls during late fetal life & after birth

12. DEVELOPMENT OF THE PRIMITIVE MOUTH (STOMODEUM)
It develops from five facial primordia:
Frontonasal prominence
It constitutes cranial boundary
Paired maxillary prominences
They form lateral boundaries
Paired mandibular prominences
They constitute caudal boundary

13. Stomodeum & Nasal Placodes

14. DEVELOPMENT OF THE NASAL CAVITY
Nasal placodes (bilateral right & left oval thickenings of surface ectoderm) develop on each side of inferior part of frontonasal prominence by the end of the fourth week.
Horseshoe-shaped elevations at margins of these placodes are formed
Medial & lateral sides of each elevation (surrounding one placode) are called as Medial & Lateral Nasal Prominences respectively
Nasal placodes now lie in depressions called Nasal Pits
Progressive deepening of nasal pits form Nasal Sacs
Medial & Lateral Nasal Prominence form a boundary of Naris
Nasal sacs are separated from oral cavity by oronasal membrane, which ruptures during the sixth week
This forms primitive choanae, which lie posterior to primitive palate
After secondary palate develops, choanae lie at junction of nasal cavity and nasopharynx
Nasal septum, incisive bone & central part of upper lip develop from merged medial nasal prominences.

15. Formation of Nasal Placodes

16. Formation of Nasal Pits & Sacs

17. Boundaries of Right Nasal Pit

18. Merging of Medial Nasal Prominences

19. Formation of Nasal Prominences

20. Beginning of Merging of Medial Nasal Prominences

21. Merging of Medial Nasal Prominences is Completed

22. Derivatives of Merged Medial Nasal Prominences

23. Development of Nasal Cavity

24. Components of Inferior Nasal Wall in Adult
View from Oral Cavity
Interpalatine suture
Secondary Palate
or Incisive bone
(primary palate)

25. Congenital Anomalies of Middle Face Area:
Oblique cleft of the face (persistent nasolacrimal grove)
It connect mouth to medial palpebral angle of the orbit
Nasolacrimal duct is present as open grove
It results from failure of fusion of lateral nasal and maxillary prominences
Cleft upper lip, superior alveolar arch and palate
It results from failure of fusion of medial nasal and maxillary prominences
They could be unilateral or bilateral

26. Bilateral Oblique Cleft of the Face

28. Unilateral Cleft Upper Lip, Superior Alveolar Arch & Palate
Right

29. Bilateral Cleft Upper Lip, Superior Alveolar Arch & Palate
After Orthopedic Correction

30. Remaining Bilateral Cleft Palate in Adult

31. DEVELOPMENT OF THE BRANCHIAL APPARATUS (arches, pouches, grooves, membranes)
Branchial arches (from 1 to 6) develop early in week 4 as neural crest cells migrate through the mesenchyme to the future head and neck region, forming elevations of mesoderm on each side of the primitive pharynx.

32. BRANCHIAL APPARATUS INCLUDES:
Branchial arches
Branchial membranes
Branchial grooves
Branchial pouches

33. A Typical Branchial Arch Contains:
An aortic arch
Derivatives of branchial arch arteries
A cartilaginous road
Derivatives of branchial arch cartilages
A nerve
Derivatives of branchial arch nerves
A muscular component
Derivatives of branchial arch muscles

34. Development of Branchial Apparatus

35. FURTHER DEVELOPMENT OF THE BRANCHIAL APPARATUS AND ITS DERIVATIVES
DEVELOPMENT OF THE LARYNX, TRACHEA, BRONCHIAL TREE, LUNGS AND PLEURA

36. Development of Lower Airway & Lungs
The lower airway and lungs develop as an outgrowth from the primitive gut.
A laryngotracheal diverticulum buds out from the primitive pharynx about the fourth week.
Its blind end forms the lung bud.
The tracheoesophageal septum separates the growing lung bud from the esophagus.
The lung bud continues to elongate and branch into bronchial buds, secondary bronchi etc.
About 24 orders of branches are eventually formed, with the last few being formed after birth.
The endoderm of the lung bud gives rise only to the epithelium and glands of the lower airway.
The mesenchyme, that surrounds the bud, gives rise to all other structures: connective tissue, cartilage, muscle, vessels & pleurae.

37. Scheme of Development of Lower Airway & Lungs

38. Scheme of Development of Lower Airway & Lungs
Bud
Bronchial

39. View of Developing Lower Airway & Lung Bud

40. Development of Laryngeal Inlet

41. Development of Trachea & Lung Buds

42. Separation of Trachea from Esophagus

43. CONGENITAL ABNORMALITIES OF TRACHEA:
Tracheoesophageal Fistula (Common):
Communication connecting trachea & esophagus that occurs in every 2500 births
It has four main varieties:
1. Superior portion of esophagus ends blindly (esophageal atresia), inferior portion joins trachea near its bifurcation (most common – 90%)
2. Esophagus has communication with trachea near its bifurcation
3. Upper end of esophagus has communication with trachea near its bifurcation, whereas the lower portion ends blindly
4. Upper end of esophagus has communication with trachea, whereas the lower portion of esophagus also has communication with trachea near its bifurcation
Tracheal Stenosis (narrowing) and Atresia (closure)
Tracheal diverticulum

44. Tracheoesophageal Fistula - 1

45. Tracheoesophageal Fistula - 2

46. Tracheoesophageal Fistula - 3

47. Tracheoesophageal Fistula - 4

48. Development of Lungs

49. Development of Lungs

50. Development of Lungs

51. Development of Lungs

52. Development of Lung Buds: 41-45 days

53. Development of Lungs: 13 weeks
Posterior View

54. Adult Lungs – Front View Not Smoker Smoker

55. Periods of Lung Development
Pseudoglandular period (5 – 17 weeks)
Canalicular period (16 – 25 weeks)
Terminal sac period (24 weeks to birth)
Alveolar period (late fetal period to 8 years after birth)

56. Periods of Lung Development
From 5-17 weeks the branching forms the bronchi and terminal bronchioles.
From weeks the diameter of the tube increases and respiratory bronchioles and alveolar ducts develop.
At 25 weeks the alveolar ducts give rise to primitive alveoli with cuboidal epithelium. By 26 weeks the alveoli have become vascularized.
By this stage the production of surfactant has begun and the fetus might survive if born prematurely.

57. Periods of Lung Development

58. Pseudoglandular (5-17 w) & Canalicular (16–25 w) Periods

59. Canalicular (16–25 w) & Terminal Sac (24w to birth) Periods

60. Periods of Lung Development
Barriers to survival born by 26 week are the small surface area available for gas exchange, lack of adequate development of the pulmonary vasculature and insufficient surfactant production.
The lung must develop further however before it is mature.
This process of maturation continues for about eight years, as the number of alveoli increase.

61. Developed Respiratory System

62. CONGENITAL ABNORMALITIES:
INFANT RESPIRATORY DISTRESS SYNDROME (IRDS):
Also called Hyaline Membrane Disease
Congenital Lung Cysts
Agenesis of Lungs or one Lung
Lung Hypoplasia
Accessory Lung
Lobe of Azygos Vein

63. Features of Respiratory Distress Syndrome
Infants born premature with weights of up to 1.5 kg show RDS
Their surfactant producing cells (type II pneumocytes & Clara cells) are not properly developed
Deficiency of pulmonary surfactant
In absence of surfactant alveoli tend to collapse during exhalation
Lungs are under inflated, alveoli contain a fluid of high protein content that resembles a hyaline (glassy) membrane
Prolonged intrauterine asphyxia may also produce irreversible changes in type II alveolar cells (responsible for surfactant production)
Infants develop rapid, labored breathing
Infants must inhale each time with extra force to reopen alveoli on next breath and they rapidly becomes exhausted

64. DEVELOPMENT OF THE PLEURA AND PLEURAL CAVITIES
Pleural cavities develop from the Intraembryonic Coelom
Right pleural cavity forms from Right Pericardio-Peritoneal Canal
Left pleural cavity forms from Left Pericardio-Peritoneal Canal
Pleurae develop from the Lateral Mesoderm of Three Laminar Embryonic Disc
Parietal Pleura – from Somatopleure
Visceral Pleura – from Splanchnopleure

65. 3 Somite Embryo of 21 Days

66. Position of Intraembryonic Coelom

67. Development of Pleural Cavities

68. Development of Pleural Cavities

69. Development of Diaphragm
Diaphragm develops from 4 sources:
1) Septum Transversum
2) Pleuroperitoneal Membranes
3) Dorsal Mesentery of Esophagus
4) Body Wall

72. Diaphragmatic Hernias

73. FETAL CIRCULATION: Oxygenated Blood
Oxygenated Blood from Placenta 
Umbilical vein 
Branch of Hepatic Portal Vein  Ductus venosus 
Inferior Vena Cava (Mixture with Venous blood) 
Right atrium 
Foramen Ovale 
Left atrium 
Left ventricle 
Aorta 
Mixture with Venous blood from Pulmonary trunk
Systemic circulation 
Umbilical artery 
Placenta 

74. FETAL CIRCULATION: Deoxygenated Blood
Venous blood from Superior Vena Cava 
Right atrium 
Right ventricle 
Pulmonary trunk 
Left pulmonary artery 
Ductus arteriosus 
Left end of aortic arch 
Descending aorta: Mixture with Arterial blood 
Umbilical artery 
Placenta 

75. Prenatal circulation

76. Aeration of Lung at Birth
Lungs at birth are half filled with amniotic fluid because breathing movements occur before birth to cause aspiration of amniotic fluid into the lungs
Fluid in lungs is cleared by three routes:
Through mouth and nose by pressure on thorax during delivery
Into pulmonary capillaries and blood vessels
Into lymphatic capillaries and vessels

77. CHANGES THAT OCCUR AFTER BIRTH
After birth, the circulation of fetal blood through the placenta ceases:
Delivery of oxygenated blood to fetus via umbilical vein ceases
The sphincter of ductus venosus constricts so all blood entering the liver passes through the hepatic sinusoids
Fall of blood pressure in the IVC and right atrium occur
Hypoxia of all tissues is increasing
Respiratory centers of the brain stem are stimulated by carbon dioxide
Inspiratory muscles contract, thoracic cage is expanded
Expansion of the lungs and First Breath takes place
Inspired air enters respiratory passageways, pushes the contained fluids out of the way and inflates the bronchial and respiratory trees
Infant’s lungs begin to function and newborn infant utters a loud cry

78. CHANGES THAT OCCUR AFTER BIRTH
Fall in pulmonary vascular resistance
Ductus arteriosus constricts
Increase in pulmonary blood flow
Left atrium pressure becomes higher than in right atrium
Valve of oval foramen is pressed against septum secondum
Foramen ovale closes

79. Postnatal circulation

80. THANK YOU