What structures are included in the lower respiratory system?

The lower respiratory system is primarily responsible for the conduction of air to the lungs and the exchange of gases during respiration. It includes several critical structures that facilitate these functions. The trachea, bronchi, and bronchioles are all integral components of this system.

The trachea, often referred to as the windpipe, is the main airway that leads from the larynx down into the thoracic cavity, where it divides into the left and right bronchi. These bronchi branch off into progressively smaller air passages known as bronchioles, which ultimately lead to the alveoli—tiny air sacs where gas exchange occurs. This hierarchical structure allows for effective distribution of air throughout the lungs and plays an essential role in respiratory mechanics.

In contrast, the other options include structures that do not belong to the lower respiratory system. For example, the nasal cavity and larynx are part of the upper respiratory system, as is the pharynx, while the diaphragm, although crucial for breathing, is a muscle that aids in respiratory movement rather than being a part of the respiratory tract itself. The thorax refers to the chest area, which houses the lungs but does not constitute a structure within the lower respiratory system. Thus, the inclusion of