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fluctuations in the internal and
external environments are constant for
living organisms the body responds to
these fluctuations by a process called
homeostasis the process of maintaining a
relatively stable internal environment
we will look at fluctuations in blood
glucose levels as an example of
homeostasis you are studying for a
biology exam about to review the chapter
on cellular respiration and decide you
need a little extra energy you consume
an entire 32 ounce bottle of soda
approximately one liter
your mid study snack contained 100 grams
of sugar and 400 calories at first you
might have a burst of energy but 30
minutes later you begin to feel
light-headed and can't seem to keep your
eyes open or your mind from wandering
what happened to understand this
unexpected result we'll explore how your
metabolism can get out of balance and
how your body works to bring it back to
normal
the cells of your body are fueled by
glucose molecules that travel throughout
your body in the bloodstream because
glucose is so important your body
responds to fluctuations in blood
glucose levels to maintain stable levels
through homeostasis after consuming food
the mouth and stomach begin the process
of mechanical and chemical digestion the
partially digested food moves from the
stomach to the small intestine where
larger molecules are further broken down
smaller molecules like the
monosaccharides glucose and fructose are
absorbed by the cells lining the
intestine glucose passes out of the
cells and into the interstitial fluid
then into the bloodstream
once individual glucose molecules move
into your bloodstream your blood glucose
level rises rapidly the high sugar
content of the soda causes a spike in
blood glucose triggering a hyperglycemic
condition the pancreas detects an
increase in glucose levels in the
bloodstream in response the beta cells
of the pancreas islets produce and
secrete the hormone insulin into the
bloodstream
insulin binds to cell surface receptors
and stimulates the transport of glucose
into the cells of the body because of
this rapid increase of insulin in
response to the large amount of glucose
from the soda too much glucose is
removed from the blood and stored as
glycogen inside liver and muscle cells
as a result your blood is now glucose
deficient a hypoglycemic condition this
low blood glucose level can cause
lightheadedness fatigue and hunger in
response to glucose deficient blood the
alpha cells of the pancreatic islets
will produce and secrete the hormone
glucagon once glucagon levels rise in
the bloodstream
glucagon will diffuse out of the blood
and bind to cell surface receptors in
the liver triggering the conversion of
glycogen to glucose in liver cells the
stored glucose is released back into the
bloodstream until homeostasis has been
achieved
turn back the clock what would happen if
you ate an apple a handful of pistachios
or some popcorn instead of a liter of
soda the consumption of complex
carbohydrates instead of simple sugars
like the ones found in the soda results
in a lower spike in blood glucose
complex carbohydrates like those found
in healthier snacks take longer to
digest so glucose is slower to enter the
bloodstream homeostasis of blood glucose
levels is more easily maintained because
the drastic changes to glucose
concentrations are diminished without
feelings of hunger or fatigue the hunger
experience during bouts of low blood
sugar in addition to disrupting
short-term homeostasis can be a
contributing factor to overeating and
long term problems like obesity glucose
is also taken up by adipose cells during
the spike in blood glucose and can be
converted into fat this along with
exaggerated portion size sedentary
lifestyles and poor nutritional choices
are contributors to the worldwide
obesity epidemic by consuming more
calories from natural sources containing
complex carbohydrates your body can
maintain homeostasis of blood glucose
levels more effectively this can reduce
your risk of gaining weight and improve
your overall health it can even help you
keep focused while studying for that
important biology exam

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