Question

The structural and functional unit of lung is

• A. Alveoli
• B. Trachea
• C. Bronchiole
• D. Bronchus

Answer 1

The correct option is A Alveoli

Lungs are the organs of ventilation in terrestrial animals. In humans, nostrils lead to trachea or wind pipe through nasopharynx. Trachea is a straight tube extending up to the mid-thoracic cavity, which divides at the level of 5th thoracic vertebra into a right and left primary bronchi. Each bronchi undergoes repeated divisions to form the secondary and tertiary bronchi and bronchioles ending up in very thin terminal bronchioles. The tracheae, primary, secondary and tertiary bronchi, and initial bronchioles are supported by incomplete cartilaginous rings. Each terminal bronchiole gives rise to a number of very thin, irregular walled and vascularised bag-like structures called alveoli. The branching network of bronchi, bronchioles, and alveoli comprise the lungs.

So, the correct answer is option A.