3.5.5 Feedback Mechanisms (AQA A2 Biology)

Overview of feedback mechanisms involved in human biology. Includes negative feedback, positive feedback and oestrous cycle (hormones incl. FSH, LH, oestrogen and progesterone) which are on the AQA A2 syllabus.

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  • Created on: 01-05-14 18:13
Preview of 3.5.5 Feedback Mechanisms (AQA A2 Biology)

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3.5.5 Negative feedback helps maintain an optimal internal state in the context of dynamic
equilibrium. Positive feedback also occurs
THE PRINCIPLES OF FEEDBACK MECHANISMS
Negative feedback restores systems to their original level.
The possession of separate mechanisms involving negative feedback
controls departures in different directions from the original state, giving
a greater degree of control.
Positive feedback results in greater departures from the original levels.
Positive feedback is often associated with a breakdown of control
systems, e.g. in temperature control.
What is a feedback loop?
A feedback loop informs the receptor of changes to the system brought about by
the effector.
When an effector has returned from a deviation of the set point, it is important that
the information is returned back to the receptor so it doesn't overcorrect and deviate
in the opposite direction. There are two types:
Negative feedback: The corrective measures are turned off.
Positive feedback: The corrective measures stay turned on.
Negative Feedback
Negative must happen otherwise the corrective measure overshoots which causes
further deviation. For example, if the body was too hot and thermoreceptors in the
hypothalamus sense this they stimulate the effector (sweat glands, vasodilation etc)
to cool the body down. Once the body returned to the set point the negative feedback
loop would be cool blood passing through the thermoreceptors and stopping the
cooling measures (effector) otherwise the body would keep dropping in temperature
until hypothermia and death.
Having different feedback loops for different systems helps maintain better
homeostatic control.
Positive Feedback
Very rarely happens but does when sodium ions pass through gated channels in
neurones causing a faster action potential. More often happens in the breakdown of
systems. When hypothermia happens, the body tends to break down causing positive
feedback so the body gets colder.
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Negative feedback helps maintain an optimal internal state in the context of dynamic
equilibrium. Positive feedback also occurs
CONTROL OF THE OESTRUS CYCLE
Mammalian oestrus is controlled by FSH, LH, progesterone and
oestrogen.
The secretion of FSH, LH, progesterone and oestrogen is controlled by
interacting positive and negative feedback loops.…read more

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Negative feedback helps maintain an optimal internal state in the context of dynamic
equilibrium.…read more

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Negative feedback helps maintain an optimal internal state in the context of dynamic
equilibrium. Positive feedback also occurs
w
n
IN MORE DETAIL...
1. Menstrual cycle begins when the
uterus lining is shed.
2. FSH released from pituitary
stimulating follicle.
3. Follicles secrete small amounts
of oestrogen to build the uterus
lining and inhibit LH and FSH
through negative feedback.
4. Follicles become more mature
secreting more oestrogen
causing positive feedback and
more FSH and LH released.
5.…read more

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