TRACHEA AND BRONCHI :::
Trachea is about four inches long and extends from larynx to the level of the fifth thoracie vertebra It is composed of 16-20 C -Shaped incomplete rings Front part of the trachea is made up of cartilage and its back part is made up of fibrous tissue The oesophagus is situated on the back of the trachea C -shaped cartilage provide semirigid support
The bronchi are formed by the bilateral bifurcation of trachea at the level of the fifth thoracic vertebra The point at which trachea divides into two branches is known as carina
The bronchi pass downwards and outwards towards the roof of both the lungs osprimary bronchi The right pronchus is shorter and wider than the left one Right bronchus is divided into upper middle and lower secondary bronchi whereas left bronchus is divided into upper and lower secondary bronchi
The secondary bronchi further form smaller tertiary or segmental bronchi which form small bronchioles Bronchioles branch further into smaller tubes called terminal bronchioles As branching increases structural changes occur in bronchi epithelium is pseudostratified cilliated columnar which changes to non ciliated simple cuboidal epithelium in terminal bronchioles The incomplete rings of cartilage in primary bronchi disappear in distal bronchioles and amount of smooth muscle increases
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