Respiratory Tract anatomy

The Respiratory Tract anatomy is very essential for understanding the functions of a lung and hence should be known to every doctor.

The Respiratory Tract anatomy starts with the oropharynx and the nasopharynx which are spaces in the mouth and the nose that act as conduit for the respiratory gases.

At carina trachea divides into right and left main bronchus. Distance of carina from upper incisors is 28 to30cm. Further right main bronchus divides into right upper, middle and lower lobe bronchus and left main bronchus into left upper and lower lobe bronchus. Right upper lobe bronchus divides into apical, posterior and anterior segment bronchi.

At carina trachea divides into right and left main Right middle lobe bronchus divides into lateral bronchus. Distance of carina from upper incisors is 28 and medial segment bronchi.

Due to shorter, wider and less acute angle chances of endotracheal tube to be positioned on right side (endobronchial intubation) are more.Children have a very different Respiratory Tract anatomy when compared to the adults. In children the angle of both right and left bronchus is same i.e., 55° up to the age of 3 years.

These segmental bronchi further divide and redivide till terminal bronchioles. Further these terminal bronchioles lose their cartilage to form respiratory bronchiole which with alveolar duct and alveolar sac forms the respiratory unit. It is at this alveolar capillary membrane where gaseous exchange takes place. The thickness of alveolar capillary membrane is 0.3 mm.

Total number of alveoli in the lungs are 300 million with have a surface area of 70 m2.

Alveolar epithelium has type I and type II cells. Type II cells secrete surfactant.

Respiratory Tract anatomy – Mucosa:

Ciliated epithelium up to terminal bronchioles after which non ciliated epithelium.

Ciliary activity is inhibited by all inhalational agents except ether.

Respiratory Tract anatomy – Arterial supply:

Bronchial artery up to terminal bronchioles and beyond terminal bronchioles by pulmonary artery.

Respiratory Tract anatomy – Nerve supply:

Parasympathetic by vagus (causes bronchoconstriction).

Sympathetic by T2 to T5 (causes bronchodila tation).

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