Our cells need oxygen to survive. One of the waste products produced
by cells is another gas called carbon dioxide. The respiratory system
takes up oxygen from the air we breathe and expels the unwanted carbon
dioxide. The main organ of the respiratory system is the lungs.
The nose and trachea
Breathing in through the nose humidifies the air. Nose hairs help to
trap any particles of dust. The warmed air enters the lungs through the
windpipe, or trachea. The trachea is a hollow tube bolstered by rings of
cartilage to prevent it from collapsing.
The lungs are inside the chest, protected by the ribcage and wrapped in a
membrane called the pleura. The lungs look like giant sponges, since
they are filled with thousands of tubes, branching smaller and smaller.
The smallest components of all are the air sacs, called 'alveoli'. Each
one has a fine mesh of capillaries. This is where the exchange of oxygen
and carbon dioxide takes place.
The breathing muscles
To stay inflated, the lungs rely on a vacuum inside the chest. The
diaphragm is a sheet of muscle slung underneath the lungs. When we
breathe, the diaphragm contracts and relaxes. This change in air
pressure means that air is ‘sucked’ into the lungs on inhalation and
‘pushed’ out of the lungs on exhalation. The intercostal muscles between
the ribs help to change the internal pressure by lifting and relaxing
the ribcage in rhythm with the diaphragm.
The exchange of gas
The blood containing carbon dioxide enters the capillaries lining the
alveoli. The gas moves from the blood across a thin film of moisture and
into the air sac. The carbon dioxide is then breathed out. On
inhalation, oxygen is drawn down into the alveoli where it passes into
the blood using the same film of moisture.
The respiratory system also allows us to talk. Exhaled air runs over the
vocal cords inside the throat. The sound of the voice depends on:
The tension and length of the vocal cords
The shape of the chest
How much air is being exhaled.
Problems of the respiratory system
Some common problems of the respiratory system include:
Asthma – wheezing and breathlessness caused by a narrowing of the airways
Bronchitis – inflammation of the lung’s mucous lining
Emphysema – disease of the alveoli
Hayfever – an allergic reaction to pollen, dust or other irritants
Influenza – caused by viruses
Laryngitis – inflammation of the vocal cords (larynx)
Pneumonia – inflammation of the lung.