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1.
Chemical signals11.3
Chemical
signalsare molecules
that transfer information from one
cell to another. They are
classified by how far
apartthe two cells are
and what route the molecule
has to take to get between them.
a.
Short range
If the cell making the signal is really
closeto the the target
cell, it is known as a
paracrine factor. These are important in
coordinating the growth and
function of particular tissues.
b.
Neurotransmitters
A nerve cell acts on a target cell right next to
itby secreting
molecules known as
neurotransmitters.
c.
Pheromones
Sometimes the signalling cell and the target cell are
reallyfar apart - in
different individuals.
Pheromonesare
small, volatile molecules that
disperse into the environment and can be detected by other
members of the same species.
d.
Hormones45.7
Hormonesare
molecules that are produced in specialized organs
called
glandsand are
sent to target cells in other organs via the
blood. It's the type of
delivery and not the chemical nature of the
molecule that makes it a
hormone; the same or very similar molecules can sometimes
act as hormones and sometimes as
neurotransmitters.
Hormones
are made by two types of cells:
i. Neurosecretory
cells
-specialized
neurons that receive a signal and respond by releasing
hormones into the blood or into a storage organ.
ii.
Endocrine cells
-non-nervous system
cells that produce hormones and secrete them into the blood
after receiving a signal
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