VPB 121: Veterinary Physiology - II (2+1)

TRACHEA

• The lungs are paired organs located within the thorax.
• In general, the left and right lungs have two and four lobes, respectively.  Trachea is the primary passageway of air to the lungs. It is located between larynx and bronchi.
• The tracheal wall contains cartilaginous rings to prevent collapse of the tracheal airway.
• Each tracheal ring is incomplete (not joined dorsally), which permits variations in diameter by the tracheal smooth muscle.
• The right and left bronchi and their subdivisions (bronchioles) continue all the way to the alveoli. The walls of the airways into the alveoli, particularly the bronchioles, create resistance to airflow.

• The larger the diameter of the airway,less the resistance to airflow. The diameter of the airways can be altered by the degree of contraction of the smooth muscle in these airways.
• Stimulation of the sympathetic nervous system causes relaxation of these walls, which allows air to more readily enter the lungs.
• The respiratory portion is the site of gas exchange between the air and blood and consists of the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli. This extensive branching of the respiratory channels is called the bronchial tree.
• The alveoli are thin-walled sacs where gaseous exchange occurs.