Ch. 20.1
• Physical reactions, such as sweating and rapid
heartbeat, are caused mainly by the body’s
endocrine system.
• What other things do you think are controlled by
the Endocrine System?
Hormones and the Endocrine
System
• The human body has 2 systems that regulate homeostasis:
• Nervous System
• Endocrine System
• The Nervous System works by sending nerve impulses
throughout the body.
• The Endocrine System produces chemicals that control many
of the body’s daily activities.
• The Endocrine System also regulates
long-term changes such as growth and
development.
• The endocrine system is made up of
glands.
• A gland is an organ that produces or
releases chemicals.
• Endocrine glands produce and release
their chemical products directly into the
bloodstream.
Hormones
• Hormones are the chemicals produced
by Endocrine Glands.
• Hormones turn on, turn off, speed up
or slow down activities of different
organs and tissues.
• Hormones are like chemical
messengers.
Hormone Production
• Hormones are triggered by the nerve
impulses sent out by the Nervous
System.
• When you see a scary movie, your
nerve impulses travel from the eyes to
the brain where it is processed.
• Then the brain sends a nerve impulse to
an endocrine gland where it releases
adrenaline which speeds up your heart
and increases your breathing.
Hormone Action
• Nerve impulses are lightning fast.
• Hormones are much slower, but last a lot longer.
• This is why it takes a while for your heart to slow back down
once you’ve been scared.
Target Cells
• So if Endocrine Glands release hormones into the
bloodstream, why aren’t ALL the organs it passes by affected?
• That’s because hormones are built for target specific cells.
• Target Cells are cells that recognize the hormones structure
(like a key and lock).
• They can’t work until it find the right lock to open.
Functions of Endocrine Glands
• The Endocrine glands include:
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Hypothalamus (brain)
Pituitary (brain)
Thyroid (throat)
Parathyroid (throat)
Adrenal (above the kidneys)
Thymus (near the heart)
Pancreas (near the intestines)
Ovaries (Female)
Testes (Male)
Hypothalamus
• Tiny part of the brain near the middle of your head.
• Links the Nervous System with the Endocrine System.
• Controls:
• Sleep
• Hunger
• Other basic impulses
for HOMEOSTASIS!
Pituitary Gland
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Below the Hypothalamus.
Size of a pea.
Controls the other Endocrine Glands.
Works closely with the Hypothalamus.
Thyroid
• In neck.
• Controls the release of energy from food molecules inside
cells.
Parathyroid Gland
• Also in the neck.
• Regulates the amount of calcium in the blood.
Thymus Gland
• Help the immune system during childhood.
Pancreas
• Produces insulin and glucagon.
• Which control the level of glucose in the blood (blood sugar
levels)
Adrenal Glands
• You have 2, one above each kidney
• Adrenaline is produced here.
• Control the amount of salt and water balance in the kidneys
and sugar in the blood.
Ovaries
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In women.
Produces eggs.
Controls changes in the female body.
Produces Estrogen and Progesterone.
Testes
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In men.
Release testosterone.
Controls changes in the male’s body
Regulates sperm production.
Negative Feedback
• Negative Feedback means the endocrine gland is turned off
when it realizes enough of the stuff it is making is floating
around the body.
• When the amount of a particular hormone in the blood
reaches a certain level, the endocrine system sends signals
that stop the release of that hormone.
Draw the Negative Feedback
Here
• Pg. 671 (red and green diagram on right)