Bronchi is the name of the caliber airway present in the respiratory tract. It conducts air into the lungs. However, no gas exchange takes place here.
The Primary Bronchi is also known as the main Bronchi. There are two of them in human body, one at the right and one at the left. Actually the windpipe or the trachea divides into the Main bronchi. The left primary bronchi subdivides into two lobar bronchi and the right one divides into three. The cartilage and the mucous membrane of primary bronchi is the same as trachea.
On the other hand, the secondary Bronchi is a branch of the primary bronchi. Each of the secondary Bronchi acts as the airway to a specific lobe of the lung. There are organs in the Secondary Bronchi that give structural support to the bronchus and also maintain the potency of lumen. It also removed debris and dust from the lungs.