There are several synonyms for the word "tracheas," which refer to the main air passages that lead into the lungs of many animals. In humans, tracheas are also known as windpipes. Other synonyms for tracheas include bronchi, bronchial tubes, and respiratory tracts. The bronchi are the two main branches that branch off from the trachea and lead to the lungs. The bronchial tubes then divide into smaller and smaller branches that eventually lead to the alveoli in the lungs, where gas exchange takes place. The respiratory tract encompasses the entire system of air passages from the nostrils to the lungs, including the nasal cavity, pharynx, larynx, trachea, bronchi, and bronchioles.