By DR QAZI IMTIAZ RASOOL
1.
Discuss feedback (negative & positive) as a common
characteristic of control system.
2.
Describe the concept of tone and antagonism in control
of body functions.
3.
Discuss other types of control as feed-foreword and
adaptive control.
4.
Describe the concept of regulated change (rheostasis
versus homeostasis).
5.
Apply the knowledge gained to examples of control.
Which internal factors are being stressed in each picture?
1.Negative feedback
2.Positive feedback
3.Feed forward feedback
4. Servo-mechanisms
5. Others
1.Process by which a mechanism is activated
to restore conditions to their original state
2.It ensures that small changes don’t become too large.
3. Defending the set point
4. Main form of regulation. (most feedback systems in the body)
5. Driving the variable in the opposite direction of the initial change.
6. Multiply the error signal by some proportionate factor(cold-shiveri
(Y)
(T)
GAIN=
CORRECTION APPLIED
RESIDUAL CHANGE
(Y)
(T)
1.
It must first suffer a disturbance before it can act
2.
Delayed response
3.
Overshoots the set point
4.
FLAWS OVERCOME by : Feedforward system
(Anticipation) Predicts
Positive feedback
1.
↑es
and amplifies the actions of the body
2.
Produces more instability in the body
3.
Produces more chaos in the body
4.
Few types necessary for our survival
5.
Short-lived
6.
Controls less frequent forms of events that do not
require continuous adjustments
7.
Considered to be the uncommon loop
8. Driving the variable in the same direction of the initial
change.
Harmful Effects of Positive Feedback
Positive feedback can be harmful. e.g:
1. Fever can cause a positive feedback within homeostasis
that pushes the body temperature continually higher.>
450 c(1130 F) cellular proteins denature bringing
metabolism to a stop and death.
2. Chronic hypertension - favor the process of
atherosclerosis - narrow. This, in turn, will intensify the
hypertension bring on more damage to the walls of
blood vessels.
3. Feed-forward control
ADAPTIVE FEEDBACK CONTROL
Concept: a direct effect of stimulus on the control system
before the action of feedback signal occurs.
(prepare the body for the change).
1.
Less frequent form of regulation.
2.
Mechanism for minimizing lag time,stimulus triggers a response in
anticipation of a change in a variable.
3. Here the direct effect of the stimulus is termed disturb signal or
interfere signal. e,g 1. Shivering , smelling,Eating – sight or smell of
food causes feedforward mechanisms
,Muscle-Exercise –.
Significance of Feedback-forward :
1.
Adaptive feedback control.
2.
Makes the human body to fore-see and adapt the
environment promptly and exactly
3.
Prepare the body for the change.
Servomechanism
1.Set piont is not fixed
2. Changes from time to time
e.g stretch reflex
-Variation in the environment stimulates change
– body response can result in either increase or decrease in activity.
NOTE;-So when dealing with a body’s response to the environment it is
not just simply on or off.
 EX: insulin – bolus of food -glucose increases - glucose drops - decrease
production- lower production
2. Antagonistic control
If in the body something exists to shift homeostasis in one direction, an
mechanisms exists that produces the opposite effect.
 EX: Parasympathetic and sympathetic nervous system
1. Dynamic stability,
2. Regulated change.
3. Reset System changes the set point of a negative
feedback system
◦ Recognizes that the body does not just stay the same all
the time. There are necessary changes that occur – growth,
development of the body – permanent changes result
1. Temporary emergencies
1. Fever, set point it centrally reset to higher and the body in turn
attempts to maintain the set point – you shiver
2. Exposure to extreme cold – drives down the heart rate, blood
pressure, and respiratory rate (used during heart and operations
allow for manipulation of structures)
1. Cyclical “clocks – Circadian rhythms
1. Temp – set point varies throughout the day. Am tends to be
lower and PM tends to be slightly higher
1.
2. Sex-Hormones released in a cycle- GH, cortisol at puberty
3. Reproductive cycle -menstrual cycle
evolution by natural selection
Acclimatization
-physiological, biochemical, or anatomical change within
an individual from chronic exposure to a new environment
1.
2.
Chemical reactions in our body rely on enzymes (biological catalysts made
of proteins)
They need a reasonably high temperature to allow enough collisions with
other molecules (substrates) but not too high in case they denature (no
longer work)
37.5 °
36.5 °
37.0 °
(set point)
7.4
1.
Your cells also need an exact level of glucose in the
blood.
2.
Excess glucose gets turned into glycogen in the liver
3.
This is regulated by 2 hormones (chemicals) from the
pancreas
Insulin Glucagon
If there is too
much glucose in
the blood, Insulin
converts some of
it to glycogen
Glycogen
Glucose in the blood
If there is not enough
glucose in the blood,
Glucagon converts
some glycogen into
glucose.
Glycogen
Glucose in the blood
The glucose in the
blood increases.
Glycogen
But there is no
insulin to convert i
into glycogen.
Glucose
concentration
rises to
dangerous
levels.
Glucose in the blood
Glucose
Concentration
Glucose levels rise
after a meal.
Insulin is produced
and glucose levels
fall to normal
again.
Normal
Meal eaten
Time
Glucose
Concentration
Glucose levels rise
after a meal.
Diabetic
Insulin is not
produced so
glucose levels stay
high
Meal eaten
Time
The
skin
This means more heat is lost from the
surface of the skin
If the
temperature
rises, the
blood vessel
dilates (gets
bigger).
This means less heat is lost from the surface of
the skin
If the
temperature
falls, the blood
vessel
constricts (gets
shut off).
What mechanisms are there to warm
the body up?
Vasoconstriction
What mechanisms are there to warm the body up?
Piloerection
This is when the hairs on your skin “stand up” .
It is sometimes called “goose bumps” or “chicken skin”!
The hairs trap a layer of air next to the skin which is then warmed by the body heat
The air becomes an insulating layer.
HR [bpm]
70
Healthy response
HR [bpm]
70
65
60
60
Sit
50
Stand
Sit
55
50
45
40
40
35
30
0:00:00
Time
0:02:00
Healthy mean and
variance
0:04:00
0:06:00