Positive and negative feedback

seminar

1. Positive and negative feedbackPositive and negative feedback
ByBy
Ali Faris AbdulbaqiAli Faris Abdulbaqi
Hamed Mejbas Al-majedyHamed Mejbas Al-majedy

2. Many biological systems are regulated by feedback Many biological systems are regulated by feedback
mechanisms. The definition is the word “feedback” mechanisms. The definition is the word “feedback”
Back to the source of signal and whether this will inhibit Back to the source of signal and whether this will inhibit
or stimulate the source. In this seminar, we'll investigate or stimulate the source. In this seminar, we'll investigate
the difference between positive and negative feedback the difference between positive and negative feedback
as they pertain to living things and explore examples of as they pertain to living things and explore examples of
each feedback type in actioneach feedback type in action
Control & RegulationControl & Regulation
All living things, even the tiniest of bacteria, are able to All living things, even the tiniest of bacteria, are able to
function only because of the intricate and complex function only because of the intricate and complex
workings of many different systems. You obtain oxygen workings of many different systems. You obtain oxygen
because of your respiratory system, you can avoid pain because of your respiratory system, you can avoid pain
because of your nervous system, and you know when because of your nervous system, and you know when
your body needs food or rest because of your endocrine your body needs food or rest because of your endocrine
system. system.

3. These are only a few small examples of the myriad of These are only a few small examples of the myriad of
processes that are constantly taking place in your body! processes that are constantly taking place in your body!
Thankfully, you don't have to consciously think about Thankfully, you don't have to consciously think about
these systems for them to work. Many living things are these systems for them to work. Many living things are
not capable of thinking at all, yet all of their biological not capable of thinking at all, yet all of their biological
processes function flawlessly. This is because many of processes function flawlessly. This is because many of
these processes are regulated by way of feedback these processes are regulated by way of feedback
systems, in which the product of a process is used to systems, in which the product of a process is used to
regulate the production of that product. In other words, regulate the production of that product. In other words,
the product, also known as the effector , will go back the product, also known as the effector , will go back
and influence a stimulus within the system, either by and influence a stimulus within the system, either by
reducing it or by further bolstering it. reducing it or by further bolstering it.

4. Types of FeedbackTypes of Feedback
Feedback systems are classified into two different Feedback systems are classified into two different
types: positive feedback and negative feedback. types: positive feedback and negative feedback.
These terms positive and negative are not meant These terms positive and negative are not meant
to denote a good or bad response, but rather the to denote a good or bad response, but rather the
type of response the system has to the presence type of response the system has to the presence
of the effector.of the effector.

5. Positive FeedbackPositive Feedback
In positive feedback systems, the effector of a process bolsters the In positive feedback systems, the effector of a process bolsters the
stimulus, which increases the production of the product. One stimulus, which increases the production of the product. One
common example of a positive feedback system in living things common example of a positive feedback system in living things
is blood clotting. When skin is cut and a blood vessel experiences is blood clotting. When skin is cut and a blood vessel experiences
damage, platelets in the blood stream collect at the site of the cut damage, platelets in the blood stream collect at the site of the cut
and begin releasing several different chemicals (the product / and begin releasing several different chemicals (the product /
effector of the process) that signal more platelet recruitment; effector of the process) that signal more platelet recruitment;
more platelets trigger more chemical release, which trigger more more platelets trigger more chemical release, which trigger more
platelets, which trigger more chemical signals, and so on, until platelets, which trigger more chemical signals, and so on, until
the platelets and various associated proteins have plugged up the the platelets and various associated proteins have plugged up the
cut with a clotcut with a clot..

6. Positive FeedbackPositive Feedback
Another example is the process of labor and childbirth in mammals. Another example is the process of labor and childbirth in mammals.
The effector is a hormone called oxytocin, which stimulates The effector is a hormone called oxytocin, which stimulates
uterine contractions, which then cause more oxytocin release, uterine contractions, which then cause more oxytocin release,
hence more contractions. This continues until the baby is bornhence more contractions. This continues until the baby is born..
The positive feedback process of labor, in which oxytocin The positive feedback process of labor, in which oxytocin
stimulates uterine contractionsstimulates uterine contractions..
Positive feedback systems essentially cause a growing cascade Positive feedback systems essentially cause a growing cascade
reaction in which each new product further amplifies the very reaction in which each new product further amplifies the very
process that created it, ensuring a whole lot more product. They process that created it, ensuring a whole lot more product. They
are typically not ongoing processes in an individual, but rather are typically not ongoing processes in an individual, but rather
reactions to specific states of physiological stress, as we see in reactions to specific states of physiological stress, as we see in
these two examples.these two examples.

7. Positive FeedbackPositive Feedback
The child pushes on the The child pushes on the
cervix (stimulus) and cervix (stimulus) and
the signal is sent to the signal is sent to
the brain. The brain the brain. The brain
releases oxytocin to releases oxytocin to
stimulate the uterus stimulate the uterus
to contract. As the to contract. As the
baby pushes, more baby pushes, more
oxytocin is release, oxytocin is release,
completing the completing the
positive feedback. positive feedback.
This continues until This continues until
the baby is delivered.the baby is delivered.

8. Negative FeedbackNegative Feedback
In negative feedback systems, the effector of a process In negative feedback systems, the effector of a process
reduces the effect of the stimulus, which in turn decreases reduces the effect of the stimulus, which in turn decreases
the production of the product. This is a more common the production of the product. This is a more common
process in living systems as it serves to maintain process in living systems as it serves to maintain
homeostasis of organisms, their optimal internal homeostasis of organisms, their optimal internal
environment. Many different key parameters of living environment. Many different key parameters of living
things - temperature, pH, and hormone levels, for example things - temperature, pH, and hormone levels, for example
- must stay within a particular range for those organisms to - must stay within a particular range for those organisms to
thrive. Negative feedback systems maintain homeostasis thrive. Negative feedback systems maintain homeostasis
by ensuring that the product of a process does not reach by ensuring that the product of a process does not reach
excessive amounts, as the presence of a product will excessive amounts, as the presence of a product will
reduce the further stimulus and production of more reduce the further stimulus and production of more
product.product.

9. Examples of Negative FeedbackExamples of Negative Feedback
Human body temperature - The hypothalamus of a human Human body temperature - The hypothalamus of a human
responds to temperature fluctuations and responds responds to temperature fluctuations and responds
accordingly. If the temperature drops, the body shivers to accordingly. If the temperature drops, the body shivers to
bring up the temperature and if it is too warm, the body bring up the temperature and if it is too warm, the body
will sweat to cool down due to evaporationwill sweat to cool down due to evaporation..
Human blood pressure - When blood pressure increases, Human blood pressure - When blood pressure increases,
signals are sent to the brain from the blood vessels. signals are sent to the brain from the blood vessels.
Signals are sent to the heart from the brain and heart rate Signals are sent to the heart from the brain and heart rate
slows down, thus helping blood pressure to return to slows down, thus helping blood pressure to return to
normal.normal.

10. Examples of Negative FeedbackExamples of Negative Feedback
When a human is hungry, metabolism slows down to When a human is hungry, metabolism slows down to
conserve energy and allow the human to continue living conserve energy and allow the human to continue living
with less foodwith less food..
Regulation of blood sugar in humans - When blood sugar Regulation of blood sugar in humans - When blood sugar
rises, insulin sends a signal to the liver, muscles and rises, insulin sends a signal to the liver, muscles and
other cells to store the excess glucose. Some is stored as other cells to store the excess glucose. Some is stored as
body fat and other is stored as glycogen in the liver and body fat and other is stored as glycogen in the liver and
musclesmuscles..
Production of human red blood cells ( erythropoiesis) - A Production of human red blood cells ( erythropoiesis) - A
decrease in oxygen is detected by the kidneys and they decrease in oxygen is detected by the kidneys and they
secrete erythropoietin. This hormone stimulates the secrete erythropoietin. This hormone stimulates the
production of red blood cells.production of red blood cells.

11. Examples of Negative FeedbackExamples of Negative Feedback
A real life example is with glucose and insulin. When we A real life example is with glucose and insulin. When we
eat a meal a large spike in glucose happens. This eat a meal a large spike in glucose happens. This
changes our glucose range beyond the normal level. To changes our glucose range beyond the normal level. To
promote cells to use and store glucose the body releases promote cells to use and store glucose the body releases
insulin. This brings the glucose level back to normalinsulin. This brings the glucose level back to normal..
On the other side if the glucose level is too low, the body On the other side if the glucose level is too low, the body
will release glucagon. This will promote the release of will release glucagon. This will promote the release of
stored sugars (glycogen to glucose). This will pull low stored sugars (glycogen to glucose). This will pull low
glucose sugar levels back to normal. This is the glucose sugar levels back to normal. This is the
opposite feedback loop to insulin.opposite feedback loop to insulin.

12. Examples of Negative FeedbackExamples of Negative Feedback

13. What is the difference between What is the difference between
positive and negative feedbackpositive and negative feedback??
Many molecular and physiological processes are controlled Many molecular and physiological processes are controlled
by feedback mechanisms. In a feedback loop the by feedback mechanisms. In a feedback loop the
product of a process, such as the breakdown of proteins product of a process, such as the breakdown of proteins
into amino acids, has an effect on the rate of the into amino acids, has an effect on the rate of the
process. Negative feedback occurs when the rate of the process. Negative feedback occurs when the rate of the
process decreases as the concentration of the product process decreases as the concentration of the product
increases. Positive feedback occurs when the rate of a increases. Positive feedback occurs when the rate of a
process increases as the concentration of the product process increases as the concentration of the product
increases. Negative feedback controls the rate of a increases. Negative feedback controls the rate of a
process to avoid accumulation of a product. The rate of process to avoid accumulation of a product. The rate of
a process will continuously accelerate under positive a process will continuously accelerate under positive
feedback as long as substrate is available and the feedback as long as substrate is available and the
product is not consumed by some other process.product is not consumed by some other process.

14. A sample idea for Types of FeedbackA sample idea for Types of Feedback
Imagine a game of soccer between two teams. One team Imagine a game of soccer between two teams. One team
is losing, and the other one is winning. There is some is losing, and the other one is winning. There is some
time left in the game to tie the game up or even win it. time left in the game to tie the game up or even win it.
The captain of the losing team knows that something The captain of the losing team knows that something
must be done in order to make one last push to try and must be done in order to make one last push to try and
score a goal. He can use a bunch of signals - through score a goal. He can use a bunch of signals - through
words, hand motions or even a certain gaze - to sort of words, hand motions or even a certain gaze - to sort of
rouse the troopsrouse the troops..

15. A sample idea for Types of FeedbackA sample idea for Types of Feedback
As his teammates see that the leader of the team As his teammates see that the leader of the team
still has belief in all of them and their chances of still has belief in all of them and their chances of
winning the game, it gives his teammates a winning the game, it gives his teammates a
confidence boost. This confidence boost will confidence boost. This confidence boost will
improve the team's performance. Likewise, this improve the team's performance. Likewise, this
positive increase in performance will be positive increase in performance will be
recognized by the captain, who, in turn, will be recognized by the captain, who, in turn, will be
enthused by his team's improved outlook on the enthused by his team's improved outlook on the
game, and this will make him even more likely to game, and this will make him even more likely to
keep pushing his team to do better.keep pushing his team to do better.

16. A sample idea for Types of FeedbackA sample idea for Types of Feedback
On the other hand, the captain may use some On the other hand, the captain may use some
stimulating words to rouse his teammates, who stimulating words to rouse his teammates, who
will in turn react negatively and try to get him to will in turn react negatively and try to get him to
be quiet instead. As you can tell, these two be quiet instead. As you can tell, these two
scenarios are all conducted through feedback scenarios are all conducted through feedback
mechanisms: the hand signals, words and mechanisms: the hand signals, words and
reactions of the captain and his teammates.reactions of the captain and his teammates.

17. A sample idea for Types of FeedbackA sample idea for Types of Feedback
In your body, very similar events occur between In your body, very similar events occur between
body systems, locations and hormones. All of body systems, locations and hormones. All of
these feedback mechanisms serve to keep your these feedback mechanisms serve to keep your
body's internal mechanisms running smoothly. If body's internal mechanisms running smoothly. If
a feedback mechanism were to go into a feedback mechanism were to go into
overdrive, or be impaired, the team (akin to your overdrive, or be impaired, the team (akin to your
body) would either never try to tie the game up body) would either never try to tie the game up
or would fail due to the exhaustion of trying too or would fail due to the exhaustion of trying too
hard. hard.