Page 95 - NCERT Science Class 10 English Medium

Figure 5.9 Human respiratory system
Figure
Figure
5.9
Figure 5.9
Figure 5.95.9
Within the lungs, the passage divides into smaller and smaller
Do You Know? tubes which finally terminate in balloon-like structures which
are called alveoli (singular–alveolus). The alveoli provide a surface
Smoking is injurious to where the exchange of gases can take place. The walls of the alveoli
health.
contain an extensive network of blood-vessels. As we have seen
Lung cancer is one of in earlier years, when we breathe in, we lift our ribs and flatten
common causes of our diaphragm, and the chest cavity becomes larger as a result.
deaths in the world. The
upper part of respiratory Because of this, air is sucked into the lungs and fills the expanded
tract is provided with alveoli. The blood brings carbon dioxide from the rest of the body
small hair-like for release into the alveoli, and the oxygen in the alveolar air is
structures called cilia. taken up by blood in the alveolar blood vessels to be transported
These cilia help to to all the cells in the body. During the breathing cycle, when air is
remove germs, dust and taken in and let out, the lungs always contain a residual volume
other harmful particles of air so that there is sufficient time for oxygen to be absorbed
from inhaled air.
Smoking destroys these and for the carbon dioxide to be released.
hair due to which germs, When the body size of animals is large, the diffusion pressure
dust, smoke and other alone cannot take care of oxygen delivery to all parts of the body.
harmful chemicals enter Instead, respiratory pigments take up oxygen from the air in the
lungs and cause lungs and carry it to tissues which are deficient in oxygen before
infection, cough and releasing it. In human beings, the respiratory pigment is
even lung cancer.
haemoglobin which has a very high affinity for oxygen. This pigment
is present in the red blood corpuscles. Carbon dioxide is more
soluble in water than oxygen is and hence is mostly transported in
the dissolved form in our blood.

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