Respiratory system
tr acheo br on chial tr ee
The trachea, bronchi and bronchioles form the tr acheobr on chial tr ee – a system of
airways that allow passage of air into the lungs, where gas exchange occurs. These airways
are located in the neck and thorax.
• Trachea divides into right- and left- primary main bronchi. Each further divides into lobar
bronchi which in turn give rise to segmental bronchi it supply air to bronchopulmonary
segments.
• Segmental bronchi divide dichotomously, eventually giving rise to terminal bronchioles
which further terminates into respiratory bronchioles.
• Originating from each respiratory bronchioles are 2-11 alveolar ducts leading to the alveolar
sacs which are extended as a group of alveoli.
• Airway becomes progressively narrower, shorter and more numerous, and Cross sectional
area, enlarges.
• Areas of tracheobronchial tree furthest from the trachea are collectively called the "distal
respiratory tree"
Trachea and the first 16 generations of tracheobronchial tree constitute the 'conducting
zone', where no gas exchange occurs.
The smallest airway in the conducting zone is the terminal bronchiole.
The last seven generations of tracheobronchial tree constitute 'the respiratory zone', where
actual exchange of gases takes place.
, This zone consists of respiratory bronchioles, alveolar ducts and alveoli.
The respiratory zone is surrounded by an extensive network of
pulmonary capillaries. The alveolar ducts and the thin-walled
alveoli together form 'the respiratory unit.
The multiple divisions of tracheobronchial tree increase the cross-
sectional area, i.e., cross-sectional area of trachea is 2.5 cm² and
that of alveoli is 11,800 cm².
There are about 300 million alveoli in human lungs. The
pulmonary capillaries and alveoli form a 'blood-gas' interface
Neur ovascular Supply of tr achea
The trachea receives sensory innervation from the r ecur r en t lar yn geal ner ve.
Arterial supply comes from the tracheal branches of the in fer ior thyr oid ar ter y,
while
venous drainage is via the brachiocephalic, azygos and accessory hemiazygos veins.
Neur ovascular Supply of br on chi
The bronchi derive innervation from pulmonary branches of the vagus ner ve (CN
X). Blood supply to the bronchi is from branches of the br on chial ar ter ies, while
venous drainage is into the br on chial vein s.
Right bronchus Left bronchus
It is wider and shorter It is narrower and longer
Extrapulmonary part: It is 2.5 cm in Extrapulmonary part-It is 5 cm in
length length
It is more vertical and makes an It is more oblique and makes an
angle of 25° with median plane angle of 45° with median plane
It enters the hilum at the level of T5 It enters hilum at the level of T6
vertebra vertebra
Within the lung root, pulmonary The bronchus passes behind and
artery is present anteriorly to the below the pulmonary artery
bronchus. without dividing
Intrapulmonary part divides into Intrapulmonary part divides into
superior, middle and inferior lobar superior and inferior lobar
bronchi branches
tr acheo br on chial tr ee
The trachea, bronchi and bronchioles form the tr acheobr on chial tr ee – a system of
airways that allow passage of air into the lungs, where gas exchange occurs. These airways
are located in the neck and thorax.
• Trachea divides into right- and left- primary main bronchi. Each further divides into lobar
bronchi which in turn give rise to segmental bronchi it supply air to bronchopulmonary
segments.
• Segmental bronchi divide dichotomously, eventually giving rise to terminal bronchioles
which further terminates into respiratory bronchioles.
• Originating from each respiratory bronchioles are 2-11 alveolar ducts leading to the alveolar
sacs which are extended as a group of alveoli.
• Airway becomes progressively narrower, shorter and more numerous, and Cross sectional
area, enlarges.
• Areas of tracheobronchial tree furthest from the trachea are collectively called the "distal
respiratory tree"
Trachea and the first 16 generations of tracheobronchial tree constitute the 'conducting
zone', where no gas exchange occurs.
The smallest airway in the conducting zone is the terminal bronchiole.
The last seven generations of tracheobronchial tree constitute 'the respiratory zone', where
actual exchange of gases takes place.
, This zone consists of respiratory bronchioles, alveolar ducts and alveoli.
The respiratory zone is surrounded by an extensive network of
pulmonary capillaries. The alveolar ducts and the thin-walled
alveoli together form 'the respiratory unit.
The multiple divisions of tracheobronchial tree increase the cross-
sectional area, i.e., cross-sectional area of trachea is 2.5 cm² and
that of alveoli is 11,800 cm².
There are about 300 million alveoli in human lungs. The
pulmonary capillaries and alveoli form a 'blood-gas' interface
Neur ovascular Supply of tr achea
The trachea receives sensory innervation from the r ecur r en t lar yn geal ner ve.
Arterial supply comes from the tracheal branches of the in fer ior thyr oid ar ter y,
while
venous drainage is via the brachiocephalic, azygos and accessory hemiazygos veins.
Neur ovascular Supply of br on chi
The bronchi derive innervation from pulmonary branches of the vagus ner ve (CN
X). Blood supply to the bronchi is from branches of the br on chial ar ter ies, while
venous drainage is into the br on chial vein s.
Right bronchus Left bronchus
It is wider and shorter It is narrower and longer
Extrapulmonary part: It is 2.5 cm in Extrapulmonary part-It is 5 cm in
length length
It is more vertical and makes an It is more oblique and makes an
angle of 25° with median plane angle of 45° with median plane
It enters the hilum at the level of T5 It enters hilum at the level of T6
vertebra vertebra
Within the lung root, pulmonary The bronchus passes behind and
artery is present anteriorly to the below the pulmonary artery
bronchus. without dividing
Intrapulmonary part divides into Intrapulmonary part divides into
superior, middle and inferior lobar superior and inferior lobar
bronchi branches
