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Insulin is a hormone, that means it
is a chemical secreted into the blood by an endocrine organ and carried around the body to
a target organ. Insulin helps to control the amount of glucose dissolved in the blood.
Insulin prevents the blood sugar level from rising too high. It is also necessary to have
insulin in your blood for respiration to take place. Without insulin cells can only get
energy from fat and this causes serious problems. The control of blood sugar level is a
homeostatic mechanism.
The Explanation:
Insulin is secreted by the Islets of Langerhans which are special groups
of cells in the pancreas. The Islets (little islands) are endocrine organs.
If you have a large carbohydrate meal, the level of glucose in the blood
will start to rise as your digestive system turns all the starch and sugars in your food
into glucose.
If you have not had a meal for several hours your blood sugar level will
fall because your cells use up the glucose in aerobic respiration.
When your blood sugar level rises, the Islets of Langerhans secrete MORE
insulin.
When your blood sugar level falls, the Islets of Langerhans secrete LESS
insulin.
The main target organ
for insulin
is the liver. It is the liver which removes glucose from the blood by turning it into
glycogen.
All other tissues in your body need insulin to help then respire
glucose, so in a way they are also target organs.
If you eat, and eat, and eat, and eat, never mind how little exercise;
there will come a time when there is no more room for glycogen in your liver. High levels
of insulin will make you start to turn the excess glucose into FAT. Please balance your
diet!!!!!
When you fast for more than two days, your liver will run out of
glycogen, so you will have to use fat and protein to get energy.
When your blood sugar level falls too low, not only does the pancreas
make less insulin, but another endocrine gland, the adrenal gland, starts to make
adrenalin and glucocorticoids.
Adrenalin and glucocorticoids are hormones which have the opposite
effect to insulin, i.e. they help to raise blood sugar level.
The hypothalamus
detects the
conditions in your blood. It measures many things including blood sugar level. The
hypothalamus is connected to the pituitary gland
which is yet another endocrine gland.
Negative feedback is the special
mechanism for turning the hormones off after they have done their job. So when your blood
sugar level drops, the amount of insulin produced also falls, and when your blood sugar
level has risen back to normal, the amount of adrenalin and glucocorticoids falls.
Definitions
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Hormone: this is a chemical secreted directly into
the blood by an endocrine organ, it carries a message to a target organ. A hormone
is a chemical messenger.
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Endocrine Organ: this is an organ which secretes a
chemical messenger or hormone directly into the blood. (c.f. an exocrine organ.) Endocrine
organs make hormones.
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Target Organ: this is any organ which is affected
by a hormone. Almost every organ in the body is affected by one or more hormones. Target
organs ar controlled by hormones. BACK
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Hypothalamus: this is a region at the base
of the brain which monitors the conditions of your blood. It measures how much
water, salts, bicarbonate ions and sugar is present; it also measures blood temperature.
The hypothalamus helps to control the pituitary gland. BACK
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Pituitary Gland: this is the Master
Endocrine Gland. It secretes hormones which control other endocrine glands.
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Homeostasis: this is the mechanism for
keeping your internal conditions constant. Blood sugar control is one example of
homeostasis/a homeostatic mechanism. The other important ones are: osmoregulation, &
thermoregulation.
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Negative feedback: this is exactly the opposite of
positive feedback! Another page in this Web Site to explain it. It is a switching
off mechanism.
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Back to the explanation.
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