Lungs Diagram

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Our lungs consist of the millions of tiny alveoli. The alveoli and associated bronchioles give the lung a soft, spongytexture. Inaddition, there are elastic tissue, numerous nerves, and blood vessels. The pair of lungs lies free in the chest or thoracic cavity, attached to each other by the bronchi. The two lungs are not mirror images of each other. Inhumans, the right lung is the larger of the two and is partially divided into three lobes. The left lung is divided into two lobes.

A thin sheet of epithelial cells, called the pleural membrane, which encloses each of the lungs and is continuous with the lining of the chest cavity. The pleural membrane secretes a lubricating fluid that reduces friction and allows the lungs to expand and contract without being irritated. The amount of fluid secreted is quite small, and it is normally absorbed by lymph vessels as rapidly as it is produced.
Internal structure of the lungs:

Bronchi: When primary bronchus reaches to lungs, it soon divides into secondary bronchi which further divide into tertiary bronchi.

Bronchioles: The tertiary bronchi divide into bronchioles .Thebronchioles divide repeatedly and give smaller bronchioles. Each bronchiole enters into lung lobules known as lobular bronchioles. It gives rise to terminal bronchioles which further divides into respiratory bronchioles.

The respiratory bronchioles open into alveolar duct. The alveolar duct terminates in atria which is expanded passages. These in turn lead into air sacs, which later open into alveoli. The wall of the alveoli is very thin and made up of squamous epithelium. Here exchange of gases takes place easily.



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