Slides in this set
The Mechanics of Breathing
Air is a mixture of gases oxygen, nitrogen, carbon dioxide, inert gases and some water vapour.
Air enters the mouth and travels through the naval cavity, through the larynx, down the trachea, into the
right or left bronchus, and then into the alveoli.
The lungs are two spongy sac-like organs that lie in the chest. They are surrounded by a membrane
called the pleural membrane and bordered on the bottom by a sheet of muscle called the diaphragm.
Air moves from areas of higher pressure to areas of lower pressure, and it is necessary for the air
pressure in our lungs to be lower than the atmospheric air pressure.
Atmospheric air pressure is 100 kPa (kilo Pascal a measure of pressure), and in the alveoli it is 99.74
Inspiration at rest
Chest cavity is lifted up and
Diaphragm muscle flattens
out by the intercostal Air is pushed into the lungs
and contracts (moves down),
muscles, increasing the from the higher outside
increasing the volume inside
volume inside the chest pressure
the chest cavity
Expiration at rest
Diaphragm relaxes and Internal intercostal Pressure inside the lungs
moves upwards, muscles relax, decreasing increases and air is foced
decreasing the volume of the volume of the chest out of the lungs to the
the chest cavity cavity lower outside pressure…read more
Inspiration and Expiration During Exercise
The rate and depth of breathing increase.
The depth of breathing is caused by a greater expansion of the chest cavity. This
is caused by the action of three other muscles:
The sternocleidomastoid raises the sternum.
The scalene and pectoralis minor lift the ribs further.
The greater expansion of the ribcage stretches the lungs further and allows for
and allows for a larger inspiration of air.
During exercise expiration is more active, with the internal intercostal muscles
contracting to pull the ribcage inwards and downwards, the abdominals also
contract which helps to push the diaphragm up with a much more rapid
reduction in the volume of the chest cavity.
Specific example changes between rest and exercise:
Tidal volume (amount of air in one breath) can vary from 0.5 Lat rest to 3.5 L
Rate of breathing can increase from 11-14 breaths per minute up to approx 45.…read more
Lung Volumes and Capacities
Volume name Description/equation Value at rest (ml) of an Change during exercise
Tidal volume (TV) Amount of air breathed in or 500 Increases
out per breath (like a tide)
Inspiratory Reserve Volume Maximal amount of air 3100 Decreases
(IRV) forcibly inspired in addition to
Expiratory Reserve Volume Maximal amount of air 1200 Decreases
(ERV) forcibly expired in addition to
Vital Capacity (VC) Maximum amount of air 4800 Slight
exhaled after a maximal
Residual Volume (RV) Amount of air left in the lungs 1200 None
after a maximal expiration
Total Lung Capacity (TV ) Total amount of air that could 6000 None
ever be in the lungs, vital
capacity plus residual volume