<p></p><h4></h4><h2><strong>Feedback in Biology</strong></h2><b></b>

<p>

</p><p>Feedback is defined as the information gained about a
reaction to a product, which will allow the modification of the product.
Feedback loops are therefore the process whereby a change to the system results
in an alarm which will trigger a certain result. This result will either
increase the change to the system or reduce it to bring the system back to
normal.</p>

<h4><b><h2><strong>Feedback Loops</strong></h2></b></h4>

<p>A feedback loop is a biological occurrence wherein the output
of a system amplifies the system (positive feedback) or inhibits the system
(negative feedback). Feedback loops are important because they allow living
organisms to&nbsp;<strong>maintain homeostasis</strong>.&nbsp;Homeostasis&nbsp;is the mechanism that enables us to keep our
internal environment relatively constant – not too hot, or too cold, not too
hungry or tired. The level of energy that an organism needs to maintain
homeostasis depends on the type of organism, as well as the environment it
inhabits. For example, a cold-blooded fish keeps its temperature at the same
level as the water around it, and so doesn’t need to control its internal
temperature. Compare this to a warm-blooded whale in the same environment: it
needs to keep its body temperature higher than that of the water around it, and
so it will expend more energy in temperature regulation.</p>

<p><img src="@@PLUGINFILE@@/Predator%20Prey%20Cycle.png" alt="Predator Prey Cycle" width="555" height="258" class="img-responsive atto_image_button_left">Feedback loops can also occur to a larger degree: at the ecosystem level, a form of homeostasis is maintained. A good example of this is in the cycle of predator and prey populations: a boom in prey population will mean more food for predators, which will increase predator numbers. This will then lead to over predation, and the prey population will again decline. The predator population will decline in response, releasing the pressure on the prey population and allowing it to bounce back.&nbsp;</p><p><strong style="color: rgb(55, 71, 79); font-family: &quot;Open Sans&quot;; font-size: 2.143rem;"><br></strong></p><p><strong style="color: rgb(55, 71, 79); font-family: &quot;Open Sans&quot;; font-size: 2.143rem;"><br></strong></p><p><strong style="color: rgb(55, 71, 79); font-family: &quot;Open Sans&quot;; font-size: 2.143rem;"><br></strong></p><p><strong style="color: rgb(55, 71, 79); font-family: &quot;Open Sans&quot;; font-size: 2.143rem;">Positive Feedback Loops</strong><br></p><p><span style="font-size: 1rem;">A positive feedback loop occurs in nature when
the product of a reaction leads to an increase in that reaction. If we look at
a system in homeostasis, a positive feedback loop moves a system further away
from the target of equilibrium. It does this by amplifying the effects of a
product or event and occurs when something needs to happen quickly.</span></p>

<p><img src="@@PLUGINFILE@@/Greenhouse%20Gases.jpg" alt="Greenhouse Gases" width="650" height="384" class="img-responsive atto_image_button_left">Positive feedback loops are inherently unstable systems. Because a
change in an input causes responses that produce continued changes in the same
direction, positive feedback loops can lead to runaway conditions. The term
positive feedback is typically used as long as a variable has an ability to
amplify itself, even if the components of a loop (receptor, control center and
effector) are not easily identifiable. In most cases, positive feedback is
harmful, but there are a few instances where positive feedback, when used in
limited fashion, contributes to normal function.&nbsp;</p>

<h4><b><br></b></h4><h4><b><br></b></h4><h4><b><br></b></h4><h4><b><br></b></h4><h4><b><br></b></h4><h4><b><br></b></h4><h4><b><br></b></h4><h4><b>Positive Feedback Loop Example 1: Fruit Ripening</b></h4>

<p>There is a surprising effect in nature where a tree or bush will
suddenly ripen all of its fruit or vegetables, without any visible signal. This
is our first example of a positive biological feedback loop. If we look at an
apple tree, with many apples, seemingly overnight they all go from unripe to
ripe to overripe. This will begin with the first apple to ripen. Once ripe, it
gives off a gas known as ethylene (C<sub>2</sub>H<sub>4</sub>) through its skin. When
exposed to this gas, the apples near to it also ripen. Once ripe, they too
produce ethylene, which continues to ripen the rest of the tree in an effect
much like a wave. This feedback loop is often used in fruit production, with
apples being exposed to manufactured ethylene gas to make them ripen faster.</p>

<h4><strong style="font-size: 1.286rem;">Positive Feedback Loop Example 2: Childbirth</strong><br></h4>

<p><img src="@@PLUGINFILE@@/Oxytocin%20Feedback%20Loop.jpg?time=1621544152196" alt="Oxytocin Feedback Loop" width="555" height="453" class="img-responsive atto_image_button_left">When
labor begins, the baby’s head is pushed downwards and results in increased
pressure on the cervix. This stimulates receptor cells to send a chemical
signal to the brain, allowing the release of oxytocin. This oxytocin diffuses
to the cervix via the blood, where it stimulated further contractions. These
contractions stimulate further oxytocin release until the baby is born.</p><p><strong style="color: rgb(55, 71, 79); font-family: &quot;Open Sans&quot;; font-size: 1.286rem;"><br></strong></p><p><strong style="color: rgb(55, 71, 79); font-family: &quot;Open Sans&quot;; font-size: 1.286rem;"><br></strong></p><p><strong style="color: rgb(55, 71, 79); font-family: &quot;Open Sans&quot;; font-size: 1.286rem;"><br></strong></p><p><strong style="color: rgb(55, 71, 79); font-family: &quot;Open Sans&quot;; font-size: 1.286rem;"><br></strong></p><p><strong style="color: rgb(55, 71, 79); font-family: &quot;Open Sans&quot;; font-size: 1.286rem;"><br></strong></p><p><strong style="color: rgb(55, 71, 79); font-family: &quot;Open Sans&quot;; font-size: 1.286rem;"><br></strong></p><p><strong style="color: rgb(55, 71, 79); font-family: &quot;Open Sans&quot;; font-size: 1.286rem;"><br></strong></p><p><strong style="color: rgb(55, 71, 79); font-family: &quot;Open Sans&quot;; font-size: 1.286rem;"><br></strong></p><p><strong style="color: rgb(55, 71, 79); font-family: &quot;Open Sans&quot;; font-size: 1.286rem;"><br></strong></p><p><strong style="color: rgb(55, 71, 79); font-family: &quot;Open Sans&quot;; font-size: 1.286rem;"><br></strong></p><p><strong style="color: rgb(55, 71, 79); font-family: &quot;Open Sans&quot;; font-size: 1.286rem;"><br></strong></p><p><strong style="color: rgb(55, 71, 79); font-family: &quot;Open Sans&quot;; font-size: 1.286rem;">Positive Feedback Loop Example 3: Blood Clotting</strong></p>

<p>When
tissue is torn or injured, a chemical is released. This chemical causes
platelets in the blood to activate. Once these platelets have activated, they
release a chemical which signals more platelets to activate, until the wound is
clotted.</p><p><strong style="color: rgb(55, 71, 79); font-family: &quot;Open Sans&quot;; font-size: 2.143rem;">Negative Feedback Loops</strong><br></p>

<p>A
negative feedback loop occurs in biology when the product of a reaction leads
to a decrease in that reaction. In this way, a negative feedback loop brings a
system closer to a target of stability or homeostasis. Negative feedback loops
are responsible for the stabilization of a system, and ensure the maintenance
of a steady, stable state. The response of the regulating mechanism is opposite
to the output of the event.</p>

<p><img src="@@PLUGINFILE@@/Glucose.jpg" alt="Glucose" width="600" height="338" class="img-responsive atto_image_button_left">Negative feedback loops are inherently stable systems.
Negative feedback loops, in conjunction with the various stimuli that can
affect a variable, typically produce a condition in which the variable
oscillates around the set point. For example, negative feedback loops involving
insulin and glucagon help to keep blood glucose levels within a narrow
concentration range. If glucose levels get too high, the body releases insulin
into the bloodstream. Insulin causes the body’s cells to take in and store
glucose, lowering the blood glucose concentration. If blood glucose gets too
low, the body releases glucagon, which causes the release of glucose from some
of the body’s cells.</p><p><strong style="color: rgb(55, 71, 79); font-family: &quot;Open Sans&quot;; font-size: 1.715rem;"><br></strong></p><p><strong style="color: rgb(55, 71, 79); font-family: &quot;Open Sans&quot;; font-size: 1.715rem;">Example 1: Temperature
Regulation</strong></p>

<p><img src="@@PLUGINFILE@@/Body%20Temperature.jpg" alt="Body Temperature" width="555" height="312" class="img-responsive atto_image_button_left"><span style="font-size: 1rem;">Temperature
regulation in humans occurs constantly. Normal human body temperature is
approximately 98.6°F. When body temperature rises above this, two mechanisms
kick in the body begins to sweat, and vasodilation occurs to allow more of the
blood surface area to be exposed to the cooler external environment. As the
sweat cools, it causes evaporative cooling, while the blood vessels cause convective
cooling. Normal temperature is regained. Should these cooling mechanisms
continue, the body will become cold. The mechanisms which then kick in are the
formation of goose bumps, and vasoconstriction. Goosebumps in other mammals
raise the hair or fur, allowing more heat to be retained. In humans, they
tighten the surrounding skin, reducing (slightly) the surface area from which
to lose heat. Vasoconstriction ensures that only a small surface area of the
veins is exposed to the cooler outside temperature, retaining heat. Normal
temperature is regained.</span></p>

<p><strong style="color: rgb(55, 71, 79); font-family: &quot;Open Sans&quot;; font-size: 2.143rem;">Positive vs. Negative Feedback</strong></p><h2><b></b></h2>

<p>The
key difference between positive and negative feedback is their response to
change: positive feedback amplifies change while negative feedback reduces
change. This means that positive feedback will result in more of a product. Negative feedback
will result in less of a product. Positive feedback moves away from a target point while negative feedback moves
towards a target.</p><br><p></p>