Secondary bronchi arise from the primary bronchi, with each one serving as the airway to a specific lobe of the lung

Human lung

The human lungs are the organs of respiration in humans. Humans have two lungs, with the left being divided into two lobes and the right into three lobes. Together, the lungs contain approximately of airways and 300 to 500 million alveoli, having a total surface area of about in...

.

Structure

They have relatively large lumens that are lined by respiratory epithelium

Respiratory epithelium

Respiratory epithelium is a type of epithelium found lining the respiratory tract, where it serves to moisten and protect the airways. It also functions as a barrier to potential pathogens and foreign particles, preventing infection and tissue injury by action of the mucociliary escalator.-...

. There is a smooth muscle

Smooth muscle

Smooth muscle is an involuntary non-striated muscle. It is divided into two sub-groups; the single-unit and multiunit smooth muscle. Within single-unit smooth muscle tissues, the autonomic nervous system innervates a single cell within a sheet or bundle and the action potential is propagated by...

 layer below the epithelium arranged as two ribbons of muscle that spiral in opposite directions. This smooth muscle layer contains seromucous glands. Irregularly arranged plates of hyaline cartilage

Hyaline cartilage

Hyaline cartilage consists of a slimy mass, pearly bluish in colour with firm consistency and considerable collagen. It contains no nerves or blood vessels, and its structure is relatively simple....

 surround the smooth muscle. These plates give structural support to the bronchus

Bronchus

A bronchus is a passage of airway in the respiratory tract that conducts air into the lungs. The bronchus branches into smaller tubes, which in turn become bronchioles....

 and maintain the patency of the lumen.

A bronchus has cartilage plates, smooth muscle, and mucus-secreting gland-cells in its wall. It also has lining cells with cilia departing towards the mouth; this removes dust and other small debris.

Secondary bronchi of right lung

Right lung

The human right lung is divided into three lobes , superior, middle, and inferior, by two interlobular fissures:-Fissures:...

• superior lobe bronchus (or eparterial bronchus
  Eparterial bronchus
  Also known as the right superior lobar bronchus, the eparterial bronchus is a branch of the right main bronchus given off about 2.5 cm. from the bifurcation of the trachea. This branch supplies the superior lobe of the right lung and is the most superior of all secondary bronchi...
  
  )
• middle lobe bronchus