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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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…

Page 2

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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




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…

Page 3

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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



4 Progesterone Ova Uterus Maintaining lining
ry/C
orpu
s
Lute
um
Ne N Pr
gati o o
ve t g
fee f es
dba e te
ck r ro
inhi t…

Page 4

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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




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…

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