Development of repiratory system By Adhish Gautam

DEVELOPMENT OF THE

RESPIRATORY SYSTEMName- Adhish Gautam

Group-216

FORMATION OF THE LUNG BUDS

• Embryo is 4 weeks old

• respiratory diverticulum (lung bud) appears as an

outgrowth from the ventral wall of the foregut .

• Dependent upon: retinoic acid (RA) produced by

adjacent mesoderm.

• Epithelium of the internal lining of the larynx, trachea;

bronchi; lungs, is Endoderm

• The cartilaginous; muscular,; connective tissue

components of the trachea; lungs are splanchnic

mesoderm ( that surrounds the foregut)

A Embryo of approximately 25 days' gestation showing the relation

of the respiratory diverticulum to the heart, stomach, and liver.

B. Sagittal section through the cephalic end of a 5-week embryo

showing the openings of the pharyngeal pouches and the

laryngotracheal orifice.

FORMATION OF THE LUNG BUDS -2

• The diverticulum expands caudally, and two longitudinal

ridges, the tracheoesophageal ridges, separate it from the

foregut.

• These ridges fuse to form the tracheoesophageal septum

• The respiratory primordium communicates with the pharynx

through the laryngeal orifice

• Foregut Divides into:

1) Dorsal portion: Oesophagus.

2) Ventral portion: Trachea & Lung Buds.

• A-C. Successive stages in development of the respiratory

diverticulum showing the tracheoesophageal ridges and

formation of the septum, splitting the foregut into esophagus

and trachea with lung buds.

• D. The ventral portion of the pharynx seen from above

showing the laryngeal orifice and surrounding swelling.

TRACHEOESOPHAGEAL FISTULAS (TEFS)

• Abnormalities in partitioning of the esophagus and

trachea by the tracheoesophageal septum ensuing

Esophageal Atresia with or w/o TEFs.

• Approx. 1/3,000 births

• Blind pouch and the lower segment forming a

fistula with the trachea (90% of cases)

• Isolated Oesophageal Atresia

• H-type TEF without oesophageal Atresia

• A. most frequent

abnormality (90% of

cases) occurs with the

upper oesophagus

ending in a blind

pouch and the lower

segment forming a

fistula with the

trachea.

• B. Isolated

oesophageal atresia

(4% of cases).

• C. H-type

tracheoesophageal

fistula (4% of cases).

• D,E. Other variations

(each 1% of cases).

BUT THESE ABNORMALITIES ARE ASSOCIATED WITH OTHER BIRTH DEFECTS

• Including cardiac abnormalities (33% of cases)

• TEFs are a component of the VACTERL Group:

• Vertebral anomalies

• Anal Atresia

• Cardiac Defects

• Tracheoesophageal Fistula

• Esophageal Atresia,

• Renal Anomalies

• Limb Defects

• A, Tracheoesophageal fistula (TEF) in a 17-week male fetus. The upper esophageal segment

ends blindly (pointer).

• B, Contrast radiograph of a newborn infant with TEF. Note the communication (arrow)

between the esophagus (E) and trachea (T).

LARYNX

• Internal lining: originates from endoderm.

• Cartilages; muscles originate from mesenchyme of

the 4th & 6th pharyngeal arches.

• Laryngeal orifice changes from a sagittal slit to a T-

shaped opening.

• Caracteristic adult shape of the laryngeal orifice

can be recognized when mesenchyme of the two

arches transforms into the thyroid; cricoid;

arytenoid cartilages.

• Laryngeal orifice and surrounding swellings

at successive stages of development:

• A. 6 weeks.

• B. 12 weeks

TRACHEA & BRONCHI & LUNGS

• The bronchial buds forms

• 5th week, each of these buds enlarges

to form right and left main bronchi.

• The right forms three secondary

bronchi.

• The left forms two.

• Stages in development of the trachea and lungs:

• A. 5 weeks.

• B. 6 weeks.

• C. 8 weeks

FURTHER DEVELOPMENT

• Subsequent growth in caudal and lateral directions, the

lung buds expand into the body cavity .

• The spaces for the lungs, which are the

pericardioperitoneal canals, are narrow.

• The mesoderm[covers outside of the lung] develops into

the visceral pleura.

• The somatic mesoderm layer[covering the body wall

from the inside] becomes the parietal pleura

• The space between the parietal and visceral pleura is

the pleural cavity .

• Expansion of the lung buds into the pericardioperitoneal canals. At this

stage, the canals are in communication with the peritoneal and

pericardial cavities.

• A. Ventral view of lung buds.

• B. Transverse section through the lung buds showing the

pleuropericardial folds that will divide the thoracic portion of the body

cavity into the pleural and pericardial cavities.

• pericardioperitoneal

canals separate from

the pericardial and

peritoneal cavities,

• the lungs expand in

the pleural cavities.

• Note the visceral

and parietal pleura

and definitive

pleural cavity. The

visceral pleura

extends between the

lobes of the lungs.

SURFACTANT

• Important for survival of the premature infant.

• When insufficient, the air-water (blood) surface

membrane tension becomes high, bringing great

risk that alveoli will collapse during expiration.

• Resulting in respiratory distress syndrome (RDS)

• Common cause of death in the premature infant.

THE END