3. The primary function is to
obtain oxygen for use by
body's cells & eliminate
carbon dioxide that cells
produce
Includes respiratory airways
leading into (& out of)
lungs plus the lungs
themselves
Pathway of air: nasal
cavities (or oral cavity) >
pharynx > trachea >
primary bronchi (right &
left) > secondary bronchi >
tertiary bronchi >
bronchioles > alveoli (site of
gas exchange)
4.
5. 1.Total lung capacity: It’s the maximum volume to which the
lungs can expand and its about 5-6 liter .Vital capacity is the
maximum amount of air that a person can expel after first filling
the lung.(4.5 ltr)
2.Residual volume: It’s the air that cannot be removed from lungs
even by forceful exhalation. It is about 1 ltr.
RV=TLC-VC
3.Tidal volume: In the process of normal or tidal breathing , nearly
.5 ltr air is inspired or expired by a normal man during each
breath. This is tidal volume.
4.Dead space volume: with each breath, air first fills parts of
respiratory passage, called dead space like nasal
passage,trachea etc. on expiration , all the air in dead space
is expired first. Normal dead space volume for a man is about
150 ml.
6. The walls of alveoli are coated with a thin film
of water & this creates a potential
problem. Water molecules, including
those on the alveolar walls, are more
attracted to each other than to air, and
this attraction creates a force called
surface tension. This surface tension
increases as water molecules come closer
together, which is what happens when we
exhale & our alveoli become smaller (like
air leaving a balloon). Potentially, surface
tension could cause alveoli to collapse
and, in addition, would make it more
difficult to 're-expand' the alveoli (when
you inhaled). Both of these would
represent serious problems: if alveoli
collapsed they'd contain no air & no
oxygen to diffuse into the blood &, if 're-
expansion' was more difficult, inhalation
would be very, very difficult if not
impossible. Fortunately, our alveoli do not
collapse & inhalation is relatively easy
because the lungs produce a substance
called surfactant that reduces surface
tension.
7. Of the two barriers to respiration, airway resistance and lung
compliance, it is only the first of these, which requires
actual work to be done to overcome it. Airway resistance
to flow is present during both inspiration and expiration
and the energy required to overcome it, which represents
the actual work of breathing, is dissipated as heat.
Although energy is required to overcome compliance in
expanding the lung, it does not contribute to the actual
work of breathing as it is not dissipated but converted to
potential energy in the distended elastic tissues. Some of
this stored energy is used to do the work of breathing
produced by airways resistance during expiration.
