• Our lungs, heart and blood vessels
collaborate to ensure that body cells are well
supplied with Oxygen and give up carbon
• Body needs oxygen to process aerobic cell
• In aerobic respiration Chemical bond within
glucose molecule are sequentially broken to
release energy. Much energy stored in body
is in form of ATP.
• This aerobic respiration requires Oxygen
molecules and six carbon of glucose are
released as a carbon dioxide as a waste.
• In daily life we are continuously inhale air to the lung
and exhale the carbon dioxide out. This cycle is called
• The air stays in lung for only brief moment but that brief
second is enough for diffusion of gas
• Oxygen in lung tissue diffuses into the blood stream.
• The movement of the gas is also called gas exchange
and there are two locations where gas exchange
• In lungs oxygen moves from air to the lungs in to the
• In capillary bed oxygen diffuse out of the blood stream
and into the body cell and carbon dioxide diffuses out
of the body cell into capitally bed.
• There are some organisms without
ventilations system such as amoeba. These
organisms do not require ventilation system
as long as they are in environment with
higher concentration of air compare to
concentration of oxygen inside body.
• Other reason for ventilation is concentration
of the respiratory gases within the lungs
encourages the diffusion of each gas in a
direction that is beneficial to the body.
• The air first enter trachea
• Then your right and left primary bronchi
• Then smaller and smaller branches of
• Then very small braches called bronchi
• Finally, the air enters the small air sacs in the
lungs called alveoli
• Alveoli in the lungs are found as clusters at
the ends of the smallest bronchioles. This has
appearance that is very similar to a brunch of
• There are 300 million alveoli in each of the
• Each cluster of alveoli has a surrounding
• The blood entering these capillary beds
comes from the right ventricle via the
• The blood in pulmonary arteries is relatively
low in oxygen and high in carbon dioxide
• While this blood is in the capillary bed
surrounding a cluster of alveoli, oxygen
diffuses from the air in each alveolus across
two cell membrane.
• One of the two cell membranes is the single
cell membrane making up the wall of the
alveolus and the second is the single cell
membrane making up the wall of the capillary
• Carbon dioxide diffuses in the opposite
direction through the same two cell
membranes. As long as organism breathe
and refresh the gases within alveoli, the
concentration gradients of these two gases
will ensure diffusion of each gas in the
direction described previously.
Spherical shape of alveoli Provides a large surface area for
respiratory gases to diffuse through
Flattened, single cell thickness of each
Prevents respiratory gases from having
to diffuse through more cell layer
Most inner lining of alveolus Allows for efficient diffusion
Associated capillary bed nearby Respiratory gases do not have to diffuse
far to reach single cell thick capillaries
• Each time organism breath, a fairly complex
series of events occurs within.
• The mechanism of breathing is based on the
inverse relationship between pressure and
• An increase in volume will lead to a decrease in
• Volume will do the opposite and whatever
• The lungs are located within thoracic cavity
• The thoracic cavity is closed to the outside air,
which lungs have only one opening to the
outside air, which is trachea
• 1.The diaphragm contracts and at the same times the
abdominal muscle and intercostals muscles help to
raise the rib cage. Collectively, these action act to
increase the volume of the thoracic cavity.
• 2.After Thoracic cavity has increased its volume, the
pressure inside the cavity decreases. This leads to less
pressure pushing on the passive lung tissue.
• 3.The lungs tissue increase its volume because there is
less pressure exerted on it
• 4.This leads to a decrease in pressure inside of the
lungs, also known as a partial vacuum
• 5.Air comes in through open mouth or nasal passages
to counter the partial vacuum with in the lungs.
• Alan Damon. “Higher Level Biology.“Gas
exchange, Pearson.2007. 2010.10.17
• Michael Kent.”Advanced Biology.”Oxford
publish. Oxford. 2007.2010.10.17
• Gaseous Exchange in Human Beings . India:
TutorVista Global Pvt. Ltd, 2010. Print.
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