The document provides a comprehensive overview of the embryological development of the respiratory system, including the formation of lung buds, larynx, trachea, bronchi, and lungs, along with their maturation stages and associated congenital abnormalities. Key periods like the pseudoglandular, canalicular, and terminal sac stages are detailed, highlighting the ongoing development of respiratory structures and the critical role of surfactant production. It also describes various congenital anomalies affecting the respiratory system, their implications, and diagnostic approaches.

1. Embryology Of The Respiratory System
thoracic cage, bones and muscles ,upper
airway ,the lungs, lung segments
Presenter:- Dr. Abdinasir
Tutor:- prof abdulaziz

2. OUTLINE
• Formation of lung buds
• Development of larynx and epiglottis
• Development of trachea
• Development of bronchi and lungs
• Lung maturation
• Congenital anomalies of the respiratory
system
• Anotomy of the respiratory system

3. Formation Of The Lung Buds
• When the embryo is approximately 4 weeks old (28), the respiratory diverticulum
(lung bud) appears as an outgrowth from the ventral wall of the foregut.
• Epithelium of the internal lining of the larynx, trachea, and bronchi, as well as
that of the lungs, is entirely of endodermal origin.
• The cartilaginous, muscular, and connective tissue components of the trachea
and lungs are derived from splanchnic mesoderm surrounding the foregut.
• Initially, the lung bud is in open communication with the foregut . When the
diverticulum expands caudally, however, two longitudinal ridges, the
tracheoesophageal ridges, separate it from the foregut.
• Subsequently, when these ridges fuse to form the tracheoesophageal septum,
the foregut is divided into a dorsal portion, the esophagus, and a ventral portion,
the trachea and lung buds.
• The respiratory primordium maintains its communication with the pharynx
through the laryngeal orifice.

6. • The proximal part of the
respiratory diverticulum
remains tubular and forms
larynx & trachea.
• The distal end of the
diverticulum dilates to
form lung bud, which
divides to give rise to 2
lung buds (primary
bronchial buds

7. Development Of The Larynx
• The internal lining of the larynx originates from the endoderm,
but the cartilages and muscles originates from the
mesenchyme of the 4th
and 6th
pharyngeal arches.
• The sagittal slit shaped laryngeal orifices change to T-slit
shaped opening because of the rapid proliferation of this
mesenchyme.
• Recanalization of the larynx
• The laryngeal epithelium proliferates rapidly resulting in
temporary occlusion of the laryngeal lumen
• Recanalization of larynx normally occurs by the 10th
week.
• Laryngeal ventricles, vocal folds and vestibular folds are
formed during recanalization.

9. Epiglottis
pharynx.

10. Trachea

11. Bronchi and Lungs
• The lung buds form the trachea and the two lateral outpocketings
during its separation from the foregut.
• At 5th
week each of these buds enlarges to form right (3 bronchi) and
left (2 bronchi) main bronchi.
• The lung buds expand into the body cavity caudally and laterally.
• The pleuroperitoneal and the pleuropericardial folds separate the
pericardioperitoneal canals from the peritoneal and pericardial cavities
respectively. And the remaining spaces form:-
a) The primitive pleural cavity.
b) The mesoderm, develops into the visceral pleura
c) The somatic mesoderm, becomes parietal pleura
d) The space b/n the parietal and the visceral pleura is the pleural cavity.

13. further development
• Secondary bronchi divide repeatedly in a dichotomous
fashion, forming 10 tertiary (segmental) bronchi in the
right lung and 8 in the left, creating the
bronchopulmonary segments of the adult lung.
• By the end of the 6th
month, approximately 17
generations of subdivisions have formed.
• an additional six divisions form during postnatal life.
• The lungs assume a more caudal position, so that by
the time of birth, the bifurcation of the trachea is
opposite the 4th
thoracic vertebra.

15. Maturation Of The Lungs

16. Pseudoglandular Period (5-17 weeks
• Branching has continued to form terminal
bronchioles
• By 17 weeks all major elements of the lung
have formed except those involved with gas
exchange (alveoli).
• Respiration is not possible.
• Fetuses born during this period are unable to
survive.

17. Canalicular Period (16-25 weeks)
• Lung tissue becomes highly vascular.
• Lumina of bronchi and terminal bronchioles become larger.
• By 24 weeks each terminal bronchiole has given rise to two or more respiratory
bronchioles.
• The respiratory bronchioles divide into 3 to 6 tubular passages called alveolar
ducts.
• Some thin-walled terminal sacs (primordial alveoli) develop at the end of
respiratory bronchioles.
 Respiration is possible at the end of this period.
 Fetus born at the end of this period may survive if given intensive care (but usually
die because of the immaturity of respiratory as well as other systems)
• Surfactant production begins by 20 weeks and increases during the terminal stages
of pregnancy.
• Sufficient terminal sacs, pulmonary vasculature & surfactant are present to permit
survival of a prematurely born infants.

20. Terminal Sac Period (24 weeks - birth)
• Many more terminal sacs develop.
• Their epithelium becomes very thin.
• Capillaries begin to bulge into developing alveoli.
• The epithelial cells of the alveoli and the endothelial cells of the capillaries
come in intimate contact and establish the blood-air barrier.
• Adequate gas exchange can occur which allows the prematurely born fetus
to survive.
• Fetuses born prematurely at 24-26 weeks may suffer from respiratory
distress due to surfactant deficiency but may survive if given intensive
care.
• By 24 weeks, the terminal sacs are lined by:
 Squamous type I pneumocytes and
 Rounded secretory, type II pneumocytes, that produce a surfactant a
phospholipid-rich fluid capable of lowering surface tension at the air–
alveolar interface.

22. CONGENITAL ABNORMALITIES
1.Abnormalities in the development of the
larynx.
2.Tracheobronchial Abnormalities.
3. Pulmonary Under Development.
4. Bronchopulmonary foregut malformation.
5. Diaphragmatic Abnormalities.

23. Larynx developmental abnormities
1.laryngeal atresia and stenosis- failure of recanalization of the larynx, leading to
obstruction of URT, it is also called congenital high airway obstruction syndrome.
2.laryngeal web-an abnormal membranous, web like tissue is present in the lumen of
the larynx, near the vocal fold. This partially obstruct the airway. This web like tissue is
derived from endodermal cells that fail to breakout during recanalization.
3.one or more laryngeal cartilage may be absent.
4.Double/Bifid larynx or some part of it may be double. Laryngoscopy
5.Laryngoptosis-abnormal downward displacement, some part of it may lie behind the
sternum. Referred to laryngoptosis when descent is excessive or prematurely.
6.Laryngocele- is a bening, air-filled dilation or herniation of the saccule of the laryngeal
ventricle, and may extend beyond the larynx proper and forms swelling in the neck.
Types: internal laryngocele confined within the larynx
External laryngocele Extends through the thyrohyoid membrane to the neck
combined laryngocele has both

24. Cont.
• Laryngoptosis is also due to aging trauma surgical procedures neuromuscular diseases. Xray,
laryngoscopy CT or MRI.
• Laryngocele: also is due to increased intralaryngeal pressure due to singing, playing wind
instruments, or chronic cough CT/MRI extent and nature
• A. Major Laryngeal cartilages:1. thyroid cartilage shape(Shield), Function protects the vocal
cord and supports the laryngeal structure Adams apple anterior part
• 2. Cricoid cartilage ring shaped located below thyroid cartilage function provides support to
larynx and is connected to the trachea, serves attachment
• 3. Epiglottis: leaf-shaped cartilage sits above the glottis function flap that covers the glottis
during swallowing to prevent food and liquids from entering the trachea.
• 4. Arytenoid Cartilages: paired pyramid shape located on cricoid cartilages function anchor the
vocal cords and voice modulation by their movement.
• B. Minor cartilages 1. corniculate cartilages small horn-like cartilages sit atop the arytenoids
function assist in the opening and closing of the glottis, Vocal cord movement.
• 2. cuneiform: pair small rod- shaped cartilages embedded within the aryepiglottic folds.
• Function provide structural support to the vocal cords and the lateral aspects of the epiglottis.

25. Double larynx and laryngocele

26. Tracheal Developmental Abnormalities
1. Tracheal agenesis
2. Tracheal stenosis
3. Tracheomalacia
4. Tracheo-oesophageal fistula (TOF)
5. Bronchial atresia
6. Tracheal bronchus (PIG bronchus)

27. Tracheal agenesis
• Rare
• Commonly associated with maternal polyhydramnios
• Presentation is immediate and acute with severe respiratory distress,
absent cry and inability to intubate the airway.
• There are three main forms of tracheal agenesis:

28. Tracheal stenosis
• Congenital stenosis due to complete cartinogenous
rings.
• is rare.
• 50% focal, 30% generalised ,20% funnel shaped
• 90% of affected children present in the first year of
life with biphasic stridor.
• CT is useful in assessing the anatomy and has the
added advantage of angiographic capabilities.
• MRI and bronchoscopy

29. Tracheomalacia
•
Tracheomalacia, is a common incidental finding on
imaging of the chest of older patients and manifests as an
increase in tracheal diameter as well as a tendency to
collapse on expiration.
• The underlying etiology is one of reduced or abnormal
connective tissues in the trachea, particularly the
cartilaginous rings.
• Generally more than 70% of collapse of the trachea
during the expiration is considered as imaging evidence of
the tracheomalacia.

30. Trachea-esophageal fistula (TOF)
• It is abnormal communication between trachea and esophagus.
• Majority of cases are associated with the presence of esophageal atresia.
(obstruction).
• It is due to defective development of the tracheoesophageal septum.
• Symptoms are due to recurrent aspiration and include paroxysmal cough,
feeding difficulties, and recurrent pneumonia.
• Contrast esophagram is used to demonstrate the presence of a fine hair-like
structure connecting the esophagus and trachea with linear opacification of the
posterior tracheal wall
• H-type fistula may not be detected until adult life even though
symptoms may have been present from infancy. 2–4%
• Connects the adjacent trachea and esophagus, with the fistula forming the
transverse bar of the ‘H’.
• VATER complex: VACTEL complex, and ARTICLE ± V complex
• Other congenital pulmonary lesions, 2% of patients.

33. Bronchial atresia
• The upper lobe bronchi are more frequently affected by
congenital atresia of lobar or segmental bronchi.
• May be associated abnormalities such as bronchogenic cyst,
intralobar sequestration or cystic adenomatoid malformation.

34. CT shows a round opacity at the site of the
atresia, medial to the air trapping,
representing mucoid impaction just distal to
the atresia.

35. Tracheal bronchus ( Pig bronchus
• Tracheal bronchus (with some variations also known as a pig bronchus)
is an anatomical variant where an accessory bronchus originates directly
from the supracarinal trachea. The latter term (pig
bronchus or bronchus suis) is often given when the entire upper lobe
(usually right side) is supplied by this bronchus 5
.
• Pathology
• Tracheal bronchi arise from the right lateral wall of the trachea usually
at a distance of <2 cm from the level of the carina 5
.
• They can be classified into two main types:
• supernumerary: usual bronchial supply to affected lung segment is
concurrently present
• displaced: usual bronchial supply to affected lung segment is
concurrently absent.

36. Tracheal bronchus

37. DIAPHRAGMATIC ABNORMALITIES
• Hernia
• Eventeration
• Agenesis
• Diaphragmatic abnormalities may be
associated with lung malformations and cause
severe respiratory symptoms

38. Congenital diaphragmatic hernia
• is one of the commonest congenital anomalies of the thorax.
• is a birth defect where there's an abnormal opening in the diaphragm,
the muscle that separates the chest cavity from the abdomen.
• This opening allows abdominal organs, such as the stomach,
intestines, or liver, to move into the chest cavity, putting pressure on
the lungs and potentially affecting their development.
• Types
a) Boakdalek hernia (75 %) severe respiratory distress in neonates
The prognosis correlates with the degree of underlying
lung hypoplasia
b) Morgagni hernia (at front typically on the right side)
 The diagnosis is now frequently made prenatally at antenatal ultrasound or MRI

39. Congenital eventration of the diaphragm
• Is a permeant elevation of a hemidiaphragm
• Either partial or complete
• Often Right sided, due to hypoplasia of the
diaphragmatic muscle.
• Most eventerations are minor, transitory, local
diaphragmatic elevations found incidentally
within the first few years of life
• Disappear with age.

40. Diaphragmatic Agenesis
• Is an extremely rare congenital condition where
the diaphragm fails to develop properly during
fetal development.
• This results in a complete absence or severe
underdevelopment of the diaphragm, the
muscular partition separating the chest from the
abdomen.
• Consequences
• Abdominal organs Migration
• Underdevelopment and function of major organs

41. Diaphragmatic agenesis

42. CYSTIC FIBROSIS
• Autosomal recessive genetic disease that affects the exocrine function of the
lungs, liver, pancreas, small bowel, sweat glands, and the male genital system.
• It results in progressive disability and multisystem failure.
• Prevalence of approximately 1 in 2500.
• initially thought to be related to viral pneumonitis and early radiological
appearance.
• Chronic respiratory illness
• prone to develop atelectasis, focal or generalized overinflation with mucus
plugging partially obstructing the airway producing secondary hyperinflation.
• In older children chest radiographs show overinflation with bronchial wall
thickening, dilatation and bronchial mucus plugging with frank bronchiectasis.
• Bronchiectasis cavities may contain air-fluid levels
• Eventually hilar adenopathy or pulmonary hypertension resulting in large
central pulmonary arteries develops.

43. Cystic fibrosis

44. Structures of the Respiratory System

45. Nose
 External nose – portion visible on face
 Internal nose – large cavity beyond nasal vestibule
Internal nares or choanae
Ducts from paranasal sinuses and nasolacrimal ducts open into
internal nose
Nasal cavity divided by nasal septum
Nasal conchae subdivide cavity into meatuses
Increase surface area and prevents dehydration

47. Ns Nasal Cavity and SinusesCavity and Sinuses
This CT is like studying a parasagittal section of a head in
the Dissecting Room, but the sinuses are visible.

48. NASAL CAVITY AND SINUSES
• The sphenoid sinus opens into the spheno-
ethmoidal recess above the superior meatus.
• The frontal, ethmoidal and maxillary open into
the middle meatus.
• The nasalacrimal duct drains lacrimal fluid
from the conjuctival sac to the inferior meatus
of the nasal cavity

49. PHARYNX
 Starts at internal nares and extends to cricoid cartilage of larynx.
 Contraction of skeletal muscles assists in deglutition.
Functions
1. Passageway for air and food
2. Resonating chamber for voice….during vocalizing the pharynx serves
the purpose of amplifying the sound waves produced by the vibrating
of the focal folds in the larynx.
3. Houses tonsils
 3 anatomical regions
i. Nasopharynx.
ii. Oropharynx.-primary resonator for vocal sounds.
iii. Laryngopharynx.

68. Hilum
• Left hilum
– The left pulmonary artery
runs over the left main and
upper lobe bronchus
• Right hilum
– The right pulmonary artery
runs in front of the right

70. Microscopic Anatomy of Lobule of Lungs

84. Boundaries of the Mediastinum
 Boundaries
 Anterior – sternum and costal
cartilages
 Posterior – 12 thoracic
vertebrae
 Superior – thoracic inlet
 Inferior – diaphragm
 Lateral – mediastinal pleura

87. Right Para-tracheal Stripe
• From the level of the
clavicles to the azygos
vein the right edge of
the trachea is seen as a
thin white stripe.
• Normal: <3 mm
• Thickened: may
represent paratracheal
mass or enlarged lymph
node

88. Normal Aortic Knuckle
• The aortic knuckle (red
line) represents the left
lateral edge of the aorta as
it arches backwards over
the left main bronchus,
and pulmonary vessels.
• The contour of the
descending thoracic aorta
(yellow line) can be seen in
continuation from the
aortic knuckle.

89. Aorto-Pulmonary Window
• The aorto-pulmonary
window lies between the
arch of the aorta and the
pulmonary arteries.
• Between the Aortic
Knuckle (AK) and the Left
Pulmonary Artery (LPA)
• The descending aorta (DA)
marks its posterior
boundary.

90. References
• Atlas of human anatomy
• Textbook of human anatomy
• Radiological anatomy
• Radiopaedia