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can be defined as the maintenance of a constant internal environment within the
body. Sensors within our body monitor a number of things including breathing,
heart rate, body temperature and also blood sugar levels. These can also be
known as detectors, which send signals to the control centre when there is a
change, or the value has deviated from the norm. This value will then be
corrected so that the norm can be maintained.

feedback is important in homeostasis and it responds when certain conditions
change. This therefore means that receptors and effectors, i.e. muscles or
organs, carry out a series of reactions so that these conditions can remain
constant. This may also be explained by saying that a change in internal body
conditions is detected by the receptor and the information from this is sent to
control centres in brain that activate effectors to show appropriate responses.

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the medulla oblongata there are chemoreceptors which are adjacent to the
respiratory centre. These chemoreceptors are sensitive to the changes of
arterial concentration of oxygen and carbon dioxide. Nerve impulses are then
sent to control centres in medulla thus changing the rate and depth of
ventilation. The increased intake of oxygen then brings the equilibrium back to

exercise, the muscles have to metabolise faster as they require both more
oxygen and nutrients. Due to this, the heart then pumps the blood harder and
faster to keep up this demand, as the heart is doing more work to supply this
blood. This means that more oxygen is required, meaning, the response given is
breathing being increased so that oxygen is pumped to all cells quicker. Due to
homeostasis, levels of oxygen in the blood are always being measured, ensuring
oxygen, carbon dioxide and also pH levels return to their norm. Messages that
are sent to the effectors informing them that the breathing rate has to be
increased, however, will decrease again when all activity has been stopped.

also controls heart rate. The medulla which is located within the brain also
controls heart rate. It sends information or messages normally in form of
chemicals/hormones. When we are carrying out exercise the heart has to supply
oxygenated blood to the rest of the body. There is information sent to the
medulla from the muscles via the nervous system. This allows the release of
chemicals, to travel to the sinus node. The sinus node then therefore
stimulates the contractions of the heart, also increasing the force which in
turn, increases heart rate. When you are at rest, or stop exercising, another
message is sent to the medulla, which in turn releases a hormone, slowing the
heart rate. When engaging in more intense exercise, another hormone is
released, increasing heart rate to supply more oxygen to the body.

level of glucose within the blood is also controlled by homeostasis. The
maintenance of the level of glucose within the blood involves both the pancreas
and the liver. Islets of Langerhans are cells located in the pancreas and these
secrete two hormones known as insulin and glucagon. Blood sugar rises after we
have ate a meal resulting in the stimulation of the pancreas cells, releasing
more insulin, enabling the sugar uptake by cells and also the storage of sugar
within the liver and muscles. As a result, blood sugar levels are decreased. If
however, blood glucose levels are low, the body will not be able to produce the
sufficient amount of ATP needed for bodily functions. The liver then breaks glucagon
down into glucose which is then released into the blood. Glucose levels in the
blood have now risen and there is no need for the release of glucagon. During
exercise there is a demand for glucose due to the contraction of the muscles
and more energy being required and so this causes an increased uptake of
glucose to working skeletal muscles. Normal blood glucose levels however, can
be maintained during exercise by increased glucose production and the release
through the stimulation of the breakdown of glycogen and glucose synthesis from
other substances. This increase allows the maintenance of blood sugars. When we
stop exercising, receptors send information to the liver telling it to slow
down glucose production.

are four different ways in which heat can be gained or lost from the body
including radiation, evaporation, convection and conduction. Radiation is when
heat from the body is given off into the atmosphere. Evaporation is when you
sweat and the evaporation from the liquid generates heat, resulting in a
cooling effect. Convection is the process of heat leaving the body via moving
air flowing by the skin. Conduction is the transfer of heat from direct contact
with another object.

main control centre in the brain that controls body temperature is known as the
thermoregulatory centre. When we exercise, body temperature will increase as
the body is working hard in attempt to be able to have more oxygen in the blood
which then can be delivered to the muscles providing them with energy. Change
within the temperature in the blood is detected by thermoreceptors. There are
also receptors which are in the skin and they detect changes in temperature
within the environment. Homeostasis will occur due to the negative feedback
triggering homeostatic mechanisms. The hypothalamus in the brain detects
signals and sends impulses to both blood vessels and sweat glands. This
therefore increases the process of heat loss by conduction and radiation.
Increased sweatening is due to the sweat glands releasing a salty liquid onto
the skins surface, taking heat with it. Blood vessels can also dilate allowing
more blood to flow through. The blood flows close to the body’s surface meaning
that there is increased radiation. This is a process known as vasodilation.
Also due to an increased body temperature there will also be increased
sweating, and the need to drink due to thirst. When we become too cold however,
the opposite of this happens and begin to shiver as a mechanism to rise body
temperature. Heat loss will be reduced as the hairs on the skin stand so that they
are able to trap a layer of air, acting as an insulator.

conclusion, homeostasis is important as it maintains the appropriate levels
within our body that our cells need to function properly and it allows us to
adapt to environmental changes. It keeps the body at a norm, however, if
conditions are at the extreme, the negative feedback mechanism will no longer
work, resulting in death, if there is no medical help.

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