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Nasal cavity: Air is filtered. The moist surface of the lining of the nasal
cavity,, and the hairs growing from its sides, remove some
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of the tiny particles of dirt in the air. In addition, as the
inhaled air passes through the nasal cavity, its temperature
is brought close to that of the body, and it takes up water
vapour so that it becomes more moist than before.
Pharynx: Warming and moistening goes on in this common passage
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of digestive and respiratory system. Epiglottis, a flap like
muscular valve controls movement of food and air towards
their respective passages.
Larynx: This stiff box contains our vocal cords. When air passes
out of the lungs and over the vocal cords, it causes them
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to vibrate. This produces sounds on the basis of our
speech, song etc.
Trachea: ind pipe channeling air to lungs. Touch your throat to
Wind
feel the tube like structure.
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Bronchus: At its lower end the trachea or the wind pipe divides into
two bronchi-one leading to each lung.
Bronchioles: Each bronchi is further divided into smaller and smaller
branches called bronchioles.
Alveolus: These finally terminate in clusters of air sacs called
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alveoli in the lungs which are very small and numerous.
Gaseous exchange takes place here as blood capillaries
take up oxygen and expel carbon dioxide.
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Blood: Blood carries oxygen, to each and every cell of the body
and collects CO2 from them.
The whole passage from nostrils to alveolus is moist and warm.
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Do you know?
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The interior of lung is divided into millions of small chambers, thus tremendously
increasing the moist surface available for transfer of gases between air and blood.
The linings of the lungs are much folded and so their total surface is enormous. If all
alveoli of our lungs are spread out they will cover an area of nearly 160 m2. Which is
equivalent to tennis court.
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28 X Class Respiration - The energy releasing system
Think and discuss
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What will happen if the respiratory tract is not moist?
Are both lungs similar in size?
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Why are alveoli so small and uncountable in number?
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Epiglottis and passage of air
Epiglottis diverts air to Epiglottis diverts food mass
From the nasal cavity, the air goes lungs away from opening of larynx
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into the pharynx. There is a tricky
problem here. From the pharynx there
are two passages, beginning with nearly
same opening and ending into separate
ones, one to the lungs and one to the
stomach. It is important that air goes into
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one and food into the other. It is also
important that food does not enter the
tube through which air goes into the
fig-5(a): Breathing fig-5(b): Swallowing
lungs. The traffic is kept properly
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