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Similar to homeostasis (20)
homeostasis
- 1. HOMEOSTASIS
The maintenance of a steady state in
the body despite changes in the
external environment
The steady state is the optimum level
for the body functions
© 2016 Paul Billiet ODWS
- 2. A system in homeostasis
needs
Sensors to detect changes in the internal
environment
A comparator to fix the set point of the system
Effectors which bring the system back to the
set point
Feedback control. Negative feedback stops
the system over compensating (going too far)
A communication system to link the different
parts together. © 2016 Paul Billiet ODWS
- 3. A system in homeostasis
needs
Sensor
Perturbation in
the internal
environment
Return to
normal
internal
environment
Effector
Comparator
Sensor
Negative
feedback
© 2016 Paul Billiet ODWS
- 5. In animals there are two
communication systems
The endocrine system based upon
hormones
The nervous system based upon
nerve impulses.
© 2016 Paul Billiet ODWS
- 6. Hormones
Organic substances
Produced in small quantities
Produced in one part of an organism (an
endocrine gland)
Transported by the blood system
All over the body
Target organs or tissues respond to the
hormone.
© 2016 Paul Billiet ODWS
- 7. The endocrine system
Chemical signals
Specific messages
Effects may be very slow (e.g. growth
hormone over years)
Some are very fast (e.g. adrenaline which
acts in seconds).
© 2016 Paul Billiet ODWS
- 8. Nerve impulses
All nerve impulses look the same
Signals travel along nerves…
…to specific parts of the body
The nerve impulses travel very quickly
Affect their target tissues in milliseconds.
© 2016 Paul Billiet ODWS
- 9. The nervous system
The nervous system is composed of
excitable cells called neurons
Neurons have long thin extensions which
carry electrical nerve impulses
The electrical signal of the nerve impulse
needs to be converted into a chemical signal
(a neurotransmitter) so that it can pass from
nerve cell to nerve cell
The neurotransmitter is destroyed after the
signal has passed on. © 2016 Paul Billiet ODWS
- 10. The nervous system
organisation
A Central Nervous System (CNS) made of the
brain and spinal cord…
and peripheral nerves connecting it to
sensors and effectors
Stimulus
Effector
eg muscle or gland
Central Nervous
System
Receptor or Sensor
eg photoreceptor
Sensory nerve
Response
Motor nerve
© 2016 Paul Billiet ODWS
- 11. Hormone pathway
Hormone secreted
into the blood
stream
Endocrine cell
Hormone stored
in vesicles
Hormone
precursors
Hormone
synthesis
Stimulus acts on
receptor site or
directly inside cell
Chemicals stimulating the
release of the hormone © 2016 Paul Billiet ODWS