In this video we will see how a negative
feedback system works with other types
of control systems to bring about
various functions. One such system is
positive feedback system. Since it's a
feedback system, output is fed back as
input into the system just like we saw
in negative feedback. The loop of the
control system is same as that of
negative feedback system except one
change here. If there is a disturbance
which leads to increase in regulated
variable, the system works to further
increase the value of the regulated
variable. Now this means that positive
feedback system will keep on increasing
the value of the variable with no end
point this will be hazardous to any
system since it can change the variable
to non-viable values. Well to prevent
that, physiological systems have made
sure that all positive feedback systems
work under the ambit of negative
feedback system thus when a desired
value of variable is reached the process
is stopped. Let us take one example of
milk ejection reflex.
In milk ejection reflex, the ejection of
milk and also the synthesis of milk
continues till the baby is suckling. So
the sucking of nipple is sensed and the
information is sent to Control Center
leading to increase in the ejection as
well as continuous synthesis of milk. Now
this feedback loop is kept under check
by negative control by hypothalamus. Now
as soon as the baby stops sucking the
nipple, the information from the sensors
stops and also the inhibitory control
from hypothalamus takes over to stop
this positive feedback loop. So the thing
to remember is that positive feedback
systems always work under the loop of
negative feedback system otherwise it
will be hazardous and it can change the
variable to non-viable values. One other
system which works together with
negative feedback system is feed-forward
system. These control systems act in
anticipatory manner and prevent any
change in the regulated variable due to
disturbance. You might have noticed that
in feedback systems, disturbance leads to
a change in the regulated variable which
is then corrected. So there is a latent
period only after which correction takes
place. This is known as lag in the system.
Now imagine could there be a scenario
where the internal or external
disturbance which can lead to change in
the value of the variable it sends
directly and the expected change in the
variable is corrected.We will see one
example where release of insulin starts
after eating food but before entry of
glucose in blood vessel. So this is the
normal negative feedback control system
where once food is eaten it is absorbed
via gastrointestinal tract
and it causes rise in blood glucose
concentration which is sensed and the
blood glucose concentration is brought
back to normal. Now in feed forward
control systems, the disturbance itself
is sensed by control center and the
expected change is corrected. So this
loop is the feed forward control but
again you see.. since it is an anticipated
change actual variable values are
monitored by a negative feedback system.
Let's conclude this way to ensure proper
body functions in an effective manner
there are multiple control systems but
all work under the ambit of negative
feedback system.
