Transcript HOMEOSTASIS - The Open Door Web Site : Home Page

HOMEOSTASIS
Homeostasis is 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
© 2008 Paul Billiet ODWS
A system in homeostasis
needs

Sensors to detect changes in the internal
environment

A comparator which fixes the set point of the system
(e.g. body temperature).
The set point will be the optimum condition under
which the system operates
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




© 2008 Paul Billiet ODWS
A system in homeostasis
needs
Perturbation in
the internal
environment
Sensor
Comparator
Effector
Sensor
Negative
feedback
© 2008 Paul Billiet ODWS
Return to
normal
internal
environment
Communication systems
These should
consist of the
following
components
Stimulus
Sensor
Linkage
system
Effector
Reponse
© 2008 Paul Billiet ODWS
In animals there are two
communication systems
The endocrine system based upon
hormones
 The nervous system based upon
nerve impulses

© 2008 Paul Billiet ODWS
Hormones
Organic substances
 Produced in small quantities
 Produced in one part of an organism
(an endocrine gland)
 Transported by the blood system
 To a target organ or tissue where it
has a profound effect

© 2008 Paul Billiet ODWS
The endocrine system

The endocrine system produces chemical
signals

Each hormone is different and they travel
relatively quickly through the blood stream all
over the body

Their effects may be very slow (e.g. growth
hormone over years)

Some are very fast (e.g. adrenaline which acts
in seconds)
© 2008 Paul Billiet ODWS
Nerve impulses

All nerve impulses look the same

So the nervous system sends signals
along nerves to specific parts of the
body

The nerve impulses travel very quickly
and affect their target tissues in
milliseconds
© 2008 Paul Billiet ODWS
The nervous system



The nervous system is composed of
excitable cells called neurones (also
neurons)
Neurones, characteristically, have long thin
extensions which carry electrical nerve
impulses
This 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
© 2008 Paul Billiet ODWS
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
Central Nervous
System
Sensory nerve
Motor nerve
Receptor or Sensor
Effector
eg photoreceptor
eg muscle or gland
Stimulus
Response
© 2008 Paul Billiet ODWS
Hormone pathway
Endocrine cell
Hormone
synthesis
Hormone
precursors
Stimulus acts on
receptor site or
directly inside cell
Chemicals stimulating the
release of the hormone
Hormone stored
in vesicles
Hormone secreted
into the blood
stream
© 2008 Paul Billiet ODWS
Hormone pathway
Hormone
receptor site
Metabolic effect
© 2008 Paul Billiet ODWS
Target cell