Page 114 - NCERT Science Class 10 English Medium

6.3
6.3 HORMONES IN ANIMALSHORMONES IN ANIMALS
HORMONES IN ANIMALS
IN
ANIMALS
6.3
6.3 HORMONES
6.3 HORMONES IN ANIMALS
How are such chemical, or hormonal, means of information transmission
used in animals? What do some animals, for instance squirrels,
experience when they are in a scary situation? Their bodies have to
prepare for either fighting or running away. Both are very complicated
activities that will use a great deal of energy in controlled ways. Many
different tissue types will be used and their activities integrated together
in these actions. However, the two alternate activities, fighting or running,
are also quite different! So here is a situation in which some common
preparations can be usefully made in the body. These preparations
should ideally make it easier to do either activity in the near future. How
would this be achieved?
If the body design in the squirrel relied only on electrical impulses
via nerve cells, the range of tissues instructed to prepare for the coming
activity would be limited. On the other hand, if a chemical signal were to
be sent as well, it would reach all cells of the body and provide the wide-
ranging changes needed. This is done in many animals, including human
beings, using a hormone called adrenaline that is secreted from the
adrenal glands. Look at Fig. 6.7 to locate these glands.
Adrenaline is secreted directly into the blood and carried to different
parts of the body. The target organs or the specific tissues on which it
acts include the heart. As a result, the heart beats faster, resulting in
supply of more oxygen to our muscles. The blood to the digestive system
and skin is reduced due to contraction of muscles around small arteries
in these organs. This diverts the blood to our skeletal muscles. The
breathing rate also increases because of the contractions of the
diaphragm and the rib muscles. All these responses together enable the
animal body to be ready to deal with the situation. Such animal hormones
are part of the endocrine system which constitutes a second way of control
and coordination in our body.

Activity 6.3
Activity 6.3
Activity
Activity 6.36.3
Activity 6.3
n Look at Fig. 6.7.
n Identify the endocrine glands mentioned in the figure.
n Some of these glands have been listed in Table 6.1 and discussed
in the text. Consult books in the library and discuss with your
teachers to find out about other glands.

Remember that plants have hormones that control their directional
growth. What functions do animal hormones perform? On the face of it,
we cannot imagine their role in directional growth. We have never seen
an animal growing more in one direction or the other, depending on
light or gravity! But if we think about it a bit more, it will become evident
that, even in animal bodies, growth happens in carefully controlled places.
Plants will grow leaves in many places on the plant body, for example.
But we do not grow fingers on our faces. The design of the body is carefully
maintained even during the growth of children.

Control and Coordination 109

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