Positive and negative feedback loops regulate many biological processes in living things. Positive feedback loops amplify signals, as when platelets and oxytocin stimulate further platelet recruitment and contractions during blood clotting and childbirth. Negative feedback loops maintain homeostasis by reducing signals, such as when insulin and glucagon regulate blood sugar levels. Feedback loops allow biological systems and processes to function automatically without conscious control.

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 feedbackMany 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 inhibitBack to the source of signal and whether this will inhibit
or stimulate the source. In this seminar, we'll investigateor stimulate the source. In this seminar, we'll investigate
the difference between positive and negative feedbackthe difference between positive and negative feedback
as they pertain to living things and explore examples ofas 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 toAll living things, even the tiniest of bacteria, are able to
function only because of the intricate and complexfunction only because of the intricate and complex
workings of many different systems. You obtain oxygenworkings of many different systems. You obtain oxygen
because of your respiratory system, you can avoid painbecause of your respiratory system, you can avoid pain
because of your nervous system, and you know whenbecause of your nervous system, and you know when
your body needs food or rest because of your endocrineyour body needs food or rest because of your endocrine
system.system.

3. These are only a few small examples of the myriad ofThese 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 aboutThankfully, you don't have to consciously think about
these systems for them to work. Many living things arethese systems for them to work. Many living things are
not capable of thinking at all, yet all of their biologicalnot capable of thinking at all, yet all of their biological
processes function flawlessly. This is because many ofprocesses function flawlessly. This is because many of
these processes are regulated by way of feedbackthese processes are regulated by way of feedback
systems, in which the product of a process is used tosystems, 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 backthe product, also known as the effector , will go back
and influence a stimulus within the system, either byand 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 differentFeedback 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 meantThese terms positive and negative are not meant
to denote a good or bad response, but rather theto denote a good or bad response, but rather the
type of response the system has to the presencetype 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 theIn positive feedback systems, the effector of a process bolsters the
stimulus, which increases the production of the product. Onestimulus, which increases the production of the product. One
common example of a positive feedback system in living thingscommon example of a positive feedback system in living things
is blood clotting. When skin is cut and a blood vessel experiencesis blood clotting. When skin is cut and a blood vessel experiences
damage, platelets in the blood stream collect at the site of the cutdamage, 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 moremore platelets trigger more chemical release, which trigger more
platelets, which trigger more chemical signals, and so on, untilplatelets, which trigger more chemical signals, and so on, until
the platelets and various associated proteins have plugged up thethe 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 stimulatesThe 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 oxytocinThe positive feedback process of labor, in which oxytocin
stimulates uterine contractionsstimulates uterine contractions..
Positive feedback systems essentially cause a growing cascadePositive feedback systems essentially cause a growing cascade
reaction in which each new product further amplifies the veryreaction in which each new product further amplifies the very
process that created it, ensuring a whole lot more product. Theyprocess that created it, ensuring a whole lot more product. They
are typically not ongoing processes in an individual, but ratherare typically not ongoing processes in an individual, but rather
reactions to specific states of physiological stress, as we see inreactions to specific states of physiological stress, as we see in
these two examples.these two examples.

7. Positive FeedbackPositive Feedback
The child pushes on theThe child pushes on the
cervix (stimulus) andcervix (stimulus) and
the signal is sent tothe signal is sent to
the brain. The brainthe brain. The brain
releases oxytocin toreleases oxytocin to
stimulate the uterusstimulate the uterus
to contract. As theto contract. As the
baby pushes, morebaby pushes, more
oxytocin is release,oxytocin is release,
completing thecompleting the
positive feedback.positive feedback.
This continues untilThis continues until
the baby is delivered.the baby is delivered.

8. Negative FeedbackNegative Feedback
In negative feedback systems, the effector of a processIn negative feedback systems, the effector of a process
reduces the effect of the stimulus, which in turn decreasesreduces the effect of the stimulus, which in turn decreases
the production of the product. This is a more commonthe production of the product. This is a more common
process in living systems as it serves to maintainprocess in living systems as it serves to maintain
homeostasis of organisms, their optimal internalhomeostasis of organisms, their optimal internal
environment. Many different key parameters of livingenvironment. Many different key parameters of living
things - temperature, pH, and hormone levels, for examplethings - 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 homeostasisthrive. Negative feedback systems maintain homeostasis
by ensuring that the product of a process does not reachby ensuring that the product of a process does not reach
excessive amounts, as the presence of a product willexcessive amounts, as the presence of a product will
reduce the further stimulus and production of morereduce the further stimulus and production of more
product.product.

9. Examples of Negative FeedbackExamples of Negative Feedback
Human body temperature - The hypothalamus of a humanHuman body temperature - The hypothalamus of a human
responds to temperature fluctuations and respondsresponds to temperature fluctuations and responds
accordingly. If the temperature drops, the body shivers toaccordingly. If the temperature drops, the body shivers to
bring up the temperature and if it is too warm, the bodybring 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 rateSignals are sent to the heart from the brain and heart rate
slows down, thus helping blood pressure to return toslows 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 toWhen a human is hungry, metabolism slows down to
conserve energy and allow the human to continue livingconserve energy and allow the human to continue living
with less foodwith less food..
Regulation of blood sugar in humans - When blood sugarRegulation of blood sugar in humans - When blood sugar
rises, insulin sends a signal to the liver, muscles andrises, insulin sends a signal to the liver, muscles and
other cells to store the excess glucose. Some is stored asother cells to store the excess glucose. Some is stored as
body fat and other is stored as glycogen in the liver andbody fat and other is stored as glycogen in the liver and
musclesmuscles..
Production of human red blood cells ( erythropoiesis) - AProduction of human red blood cells ( erythropoiesis) - A
decrease in oxygen is detected by the kidneys and theydecrease in oxygen is detected by the kidneys and they
secrete erythropoietin. This hormone stimulates thesecrete 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 weA real life example is with glucose and insulin. When we
eat a meal a large spike in glucose happens. Thiseat a meal a large spike in glucose happens. This
changes our glucose range beyond the normal level. Tochanges our glucose range beyond the normal level. To
promote cells to use and store glucose the body releasespromote 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 bodyOn the other side if the glucose level is too low, the body
will release glucagon. This will promote the release ofwill release glucagon. This will promote the release of
stored sugars (glycogen to glucose). This will pull lowstored sugars (glycogen to glucose). This will pull low
glucose sugar levels back to normal. This is theglucose 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 betweenWhat is the difference between
positive and negative feedbackpositive and negative feedback??
Many molecular and physiological processes are controlledMany molecular and physiological processes are controlled
by feedback mechanisms. In a feedback loop theby feedback mechanisms. In a feedback loop the
product of a process, such as the breakdown of proteinsproduct of a process, such as the breakdown of proteins
into amino acids, has an effect on the rate of theinto amino acids, has an effect on the rate of the
process. Negative feedback occurs when the rate of theprocess. Negative feedback occurs when the rate of the
process decreases as the concentration of the productprocess decreases as the concentration of the product
increases. Positive feedback occurs when the rate of aincreases. Positive feedback occurs when the rate of a
process increases as the concentration of the productprocess increases as the concentration of the product
increases. Negative feedback controls the rate of aincreases. Negative feedback controls the rate of a
process to avoid accumulation of a product. The rate ofprocess to avoid accumulation of a product. The rate of
a process will continuously accelerate under positivea process will continuously accelerate under positive
feedback as long as substrate is available and thefeedback 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 teamImagine a game of soccer between two teams. One team
is losing, and the other one is winning. There is someis 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 somethingThe captain of the losing team knows that something
must be done in order to make one last push to try andmust be done in order to make one last push to try and
score a goal. He can use a bunch of signals - throughscore a goal. He can use a bunch of signals - through
words, hand motions or even a certain gaze - to sort ofwords, 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 teamAs his teammates see that the leader of the team
still has belief in all of them and their chances ofstill has belief in all of them and their chances of
winning the game, it gives his teammates awinning the game, it gives his teammates a
confidence boost. This confidence boost willconfidence boost. This confidence boost will
improve the team's performance. Likewise, thisimprove the team's performance. Likewise, this
positive increase in performance will bepositive increase in performance will be
recognized by the captain, who, in turn, will berecognized by the captain, who, in turn, will be
enthused by his team's improved outlook on theenthused by his team's improved outlook on the
game, and this will make him even more likely togame, 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 someOn the other hand, the captain may use some
stimulating words to rouse his teammates, whostimulating words to rouse his teammates, who
will in turn react negatively and try to get him towill in turn react negatively and try to get him to
be quiet instead. As you can tell, these twobe quiet instead. As you can tell, these two
scenarios are all conducted through feedbackscenarios are all conducted through feedback
mechanisms: the hand signals, words andmechanisms: 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 betweenIn your body, very similar events occur between
body systems, locations and hormones. All ofbody systems, locations and hormones. All of
these feedback mechanisms serve to keep yourthese feedback mechanisms serve to keep your
body's internal mechanisms running smoothly. Ifbody's internal mechanisms running smoothly. If
a feedback mechanism were to go intoa feedback mechanism were to go into
overdrive, or be impaired, the team (akin to youroverdrive, or be impaired, the team (akin to your
body) would either never try to tie the game upbody) would either never try to tie the game up
or would fail due to the exhaustion of trying tooor would fail due to the exhaustion of trying too
hard.hard.