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Chapter 5

BIOLOGY 2A03 Chapter 5: Chapter 5 Cell Communication

Course Code
Graham R.Scott

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Chapter 5: Cell Communication
-Cell-cell communication  important for homeostasis
-Performed by intracellular chemical messengers
1. Hormones – Any messenger that is circulated in the blood
oSecreted by endocrine cells – reach target cells via blood
Then binds to receptors on target cells
oSlow acting
oe.g. insulin, regulates glucose homeostasis
2. Neurotransmitters
oSecreted by nerve cell (at synapse w/ target cell)
Very short distance the neurotransmitter needs to
Signals can be transported very far distances
axons can be very long
oFast acting
oe.g. acetylcholine, controls heart rate
3. Autocrine/paracrine agents released by a variety of
oLocal homeostatic responses, reach target cell by
oAuto = same cell; para = neighbouring cells
oe.g. nitric oxide, regulates blood vessels
Signal Transduction Pathways
-detect intercellular messengers and convert them into a meaningful
intracellular response
-Four features
1. Speci'city: signal molecule *ts in its receptor
while others do not
2. Ampli'cation: 1 receptor binding can lead to
1,000,000 intracellular signals
3. Desensitization/adaptation: feedback can
‘shut o&’ the receptor
4. Integration: the intracellular signal can be the result of integration of
multiple receptor inputs
-Magnitude of a cell’s response is dictated by the number of receptors bound,
which depends upon
1. Messengers concentration
a. Increase (beginning with low concentration of messengers)
increases the numbers bound, but eventually will saturate the
number of receptors available
2. Number of receptors present
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