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take large gulps of air while panting, or sleep with an open mouth when the nose is
congested.
Air then passes into the pharynx, which is also involved in swallowing. The epiglottis
prevents the movement of food into the respiratory tract and the misdirection of air towards
the esophagus. When the epiglottis doesn’t function properly, small particles can enter the
trachea. These are removed through coughing. If food is lodged or stuck in the airway, it
may need to be quickly removed through abdominal thrusts, also known as the Heimlich
maneuver.
The larynx follows the pharynx and its main function is the production of sound. The flow of
air through this region can influence pitch and volume. Air then enters the trachea, a long
tube that is covered by a series of cartilaginous rings, which help this tubular structure retain
its shape during inhalation and exhalation. The trachea is lined by pseudostratified columnar
epithelia with goblet cells secreting mucins and helping to form mucus.
The trachea splits to form two primary bronchi, called the left and right bronchi. Each of
these leads towards a lung and then undergoes repeated branching to produce secondary,
tertiary bronchi and bronchioles, with successively smaller diameters. When the bronchioles
are less than a millimeter in diameter, they are called terminal bronchioles, whose purpose is
to end in vascularized alveoli. As the bronchi begin to branch, their internal structure
changes. Cartilage is more common in the larger airways, and a single epithelial layer is
common in the smallest parts of the conducting zone and the respiratory zone. Bronchi and
bronchioles both contain smooth muscles that can constrict in times of rest, or dilate during
exercise.
Lungs are made of spongy tissue containing many vascular tissues and much of the airway
that appears after the trachea. A pleural membrane allows these paired organs to expand and
contract with minimal friction. The left lung is smaller than the right due to the location of
the heart on the left side of the thoracic cavity.
Diseases of the Respiratory System
Diseases of the respiratory tract can arise due to obstruction to the airway, constriction of the
passages, or the loss of the extensive surface area of alveoli for gas exchange. There could
also be difficulties with the capillaries surrounding these alveoli, either due to clots or due to
altered cardiac function. These illnesses could be chronic conditions or temporary infections.
They could also simply be minor changes to the breathing pattern, as seen with hiccups.
Common Cold
The common cold, appropriately named for its ubiquitous nature is caused by a large number
of different viruses, with rhino viruses being the most varied and common cause for this
complaint. It is usually an infection of the upper respiratory tract, though it can occasionally
spread towards the ears or the lower respiratory structures as well. The infection is