A bronchus is a passage of airway in the respiratory tract

Respiratory tract

In humans the respiratory tract is the part of the anatomy involved with the process of respiration.The respiratory tract is divided into 3 segments:*Upper respiratory tract: nose and nasal passages, paranasal sinuses, and throat or pharynx...

 that conducts air into the lung

Lung

The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...

s. The bronchus branches into smaller tubes, which in turn become bronchioles.
No gas exchange

Gas exchange

Gas exchange is a process in biology where gases contained in an organism and atmosphere transfer or exchange. In human gas-exchange, gases contained in the blood of human bodies exchange with gases contained in the atmosphere. Human gas-exchange occurs in the lungs...

 takes place in this part of the lungs.
The trachea

Trachea

Trachea may refer to:* Vertebrate trachea, or windpipe, in terrestrial vertebrates, such as birds and mammals* Invertebrate trachea, in terrestrial invertebrates, such as insects and crustaceans* Vessel elements in plants...

 (windpipe) divides into two main bronchi (also mainstem bronchi), the left and the right, at the level of the sternal angle

Sternal angle

The sternal angle or 'angle of Louis', from the Latin angulus Ludovici is the anterior angle formed by the junction of the manubrium and the body of the sternum in the form of a secondary cartilaginous joint . This is also called the manubriosternal joint or Angle of Louis...

 at the anatomical point known as the carina.