The purpose of the respiratory system is to supply oxygen
to body tissues and to remove carbon dioxide, which is a waste product, from
the body tissues. Breathing is the process by which oxygen in the air is
brought into the lungs and into close contact with the blood, which absorbs
it and carries it to all parts of the body. At the same time, the blood gives
up carbon dioxide, which is carried out of the lungs with air breathed out.
Upper Respiratory System
The parts of the upper respiratory system are illustrated above.
The Nasal cavity or Nose is the preferred entrance for outside
air to enter into the respiratory system.
The Oral cavity or Mouth is an alternative way for air to enter
the respiratory system.
The Pharynx or Throat collects incoming air from the nose and
mouth and passes it downward to the trachea (windpipe).
The Epiglottis is a flap of tissue that guards the entrance to the
trachea, closing when anything is swallowed in order to prevent food or fluid
from entering the lungs.
The Larynx or Voice Box contains two vocal cords. Air moving
through the larynx creates voice sounds.
The Esophagus is the passage leading from the mouth and throat to
The Trachea or Windpipe is the passage leading from the pharynx
to the lungs.
The Bronchi or Tubes are the two main tubes into the lung that
divide from the trachea. The bronchi subdivide into the lobar bronchi --
three on the right side and two on the left. These, in turn, subdivide further.
Lower Respiratory System
The parts of the lower respiratory system are illustrated above.
The Bronchioles are the smallest subdivisions of the bronchi, at the
end of which are the alveoli (plural of alveolus).
The Alveoli are the very small air sacs that are the destination of
inhaled air. The capillaries are blood vessels that are imbedded in the walls
of the alveoli. The blood discharges carbon dioxide into the alveoli and
takes up oxygen from the air in the alveoli.
The Lungs are elastic organs with sponge-like tissue. Inhalation requires
an active effort, whereas exhalation occurs automatically. The right lung
is divided into three lobes and the left is divided into two lobes.
The Pleura are the two membranes (actually one continuous membrane
folded on itself) that surround each lobe of the lungs and separate the lungs
from the chest wall. The pleural space is the space between the two pleura.
Diaphragm is the strong wall of muscle that separates the chest cavity
from the abdominal cavity. By moving downwards, it creates suction to draw
in air and expand the lungs.
Ribs are bones separating and protecting the chest cavity. They move
to a limited degree, helping the lungs to expand and contract.
Muscles of the Respiratory System
There are four sets of muscles that control the respiratory system.
The Diaphragm is a dome-shaped muscle, which separates the chest from
the abdominal cavity. It is the major muscle and the one that begins the
inhalation process. During inhalation, the diaphragm contracts and moves
downwards, pushing out the abdomen and creating suction which draws in the
air and expands the lungs.
The Intercostal muscles, located between the ribs, act to increase
and decrease the diameter of the chest cage. The ability to take a deep breath
and cough is affected by the loss of the intercostal muscles.
The Abdominal muscles are the most essential for an effective cough.
When the abdominal muscles contract, the diaphragm is forced upward and coughing
or forcefully blowing out air results.
The Accessory muscles, located in the neck, act to elevate the rib
cage and can assist in deep respiration. However, they alone are not sufficient
to support deep ventilation.