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Gas exchange
Features of gas exchange in animals
•The gills of a fish are like alveoli: give oxygen to blood and take the
carbon dioxide from the blood along with other nutrients in the
•The alveoli in humans
do the same thing except
for getting nutrients.
•Lungs remain moist simply because of their location within the
•From the alveoli - the
blood then carries O2 to
all our cells via our many
capillaries, (no cell is
more than a few mm
away from one.)
•Most fish are unable to breathe on land because the structure of air
does not support their gills, leading to their collapse.
•There would also be too much water loss due to evaporation, and
both gills and lungs need to remain moist.
•When oxygen rich water is passed over their gills, the blood in the
capillaries flowing in the opposite direction to the water in a
process called counter current exchange, the fish are able to absorb
all the oxygen they require.
•The deoxygenated water then returns to the surrounding water
through openings in the side of the pharynx.
Inspired vs. expired air
Inspired air
Expired air
Oxygen %
CO2 %
Water vapor
•Body produces CO 2 due to respiration
• Nitrogen diffuses into blood and then diffuses back out (inspire/ expire)
Know the difference
 Ventilation: pumping mechanism that moves air into and
out of the lungs efficiently, thereby maintaining the
concentration gradient of diffusion
 Gas Exchange: The exchange of gases between an organism
and its surroundings (uptake of oxygen and release of
carbon dioxide in animal and plants)
 Cell Respiration: The controlled release of energy in the
form of ATP from organic compounds in cells (a
continuous process in all cells)
Intercostal Muscles
Internal and External
Intercostal Muscles
Steps to ventilation
Inspiration (inhale)
Expiration (exhalation)
Diaphragm contracts down
(pushing abdominal down)
Diaphragm relaxes and pulls
up (pressure from abdominal
pushes up)
External (ICM) contract
Internal (ICM) relax
External (ICM) relaxes
Internal (ICM) contracts
Ribs move up and out
Rib cage moves down and in
Volume of thorax cavity
Volume of thorax cavity
Air pressure of thorax drops
(below atmospheric pressure)
Air pressure of thorax rises
above atmospheric pressure
Air flows in
Air flows out
Mucus / Cillia / Gas Exchange
 Mucous Membranes - a physical barrier that
traps potential pathogens
 Epithelium cells form mucus membrane (more
fragile than skin)
 Constantly flushed with fluids ( mucus, saliva,
 CILIA in the trachea - move inhaled material trapped
in the mucous to the top of the trachea where it is
dumped down the oesophagus to be destroyed by
stomach acids (HCl)and enzymes.
 Eye lashes
 Cilia moves in unison – moving
moving along partials like a brush
Nicotine in
tobacco can
kill these cells!
Exercise on Breathing
Muscles work hard – rapid respiration
Faster respiration – more CO2 generated
CO2 goes to blood and dissolves in blood plasma
It produces a weak acid – carbonic acid (lowers pH)
Brain detects pH change
Sends signal to intercostal muscle & Diaphragm
Causing these muscles to contract hard and fast
Result – rapid breathing
Therefore fast oxygen delivery to cells / CO2 removal