Bronchi and Bronchioles

• The trachea splits into two primary bronchi which enter each lung.
• Within the lung, the bronchi split into smaller secondary bronchi which enter separate lobes.
• Within the lobes, they split into even smaller tertiary bronchi.
• Allows passage of air.
• Bronchioles are the smallest airways of the respiratory tract with a diameter of 1mm or less. They get smaller with each successive branch point where one branch divides into two.
• The most distal branches are referred to as respiratory bronchioles.
• • From the trachea to the alveoli, the airway divides 23 times. 
• The size of the airway, from the trachea to the bronchi and as it goes to the alveoli, reduces approximately 2-2.5 cm in diameter.
• From the terminal bronchioles and as it goes distally, it reduces to about less than 0.5 mm.
• As the smooth muscle thickens or increases in proportion, the lesser the cartilage is.
• • The reason why the respiratory bronchioles have a thinner layer of epithelium is because it is a part of the respiratory zone where gas exchange is taking place.
• Bronchi

  • Larger diameter
  • More cartilage
  • Thicker layer of epithelium
  • Lesser proportion of smooth muscle
• Bronchioles

  • Smaller diameter
  • Less cartilage
  • Thinner layer of epithelium
  • Greater proportion of smooth muscle