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Chapter 31 - Hormones
31-1 What Hormones Do
31-2 How Hormones Work
31-3 Glands and Their Functions
Section 31-1 What Hormones Do
• A hormone is a chemical signal that is made in
one place and delivered to another – usually
by the blood. Hormones regulate the body’s
activities.
• Organs that produce most of the hormones in
your body are called endocrine glands. The
endocrine glands secrete hormones directly
into the bloodstream.
• The hormones travel to a specific tissue or
organ called a target. Once it arrives, the
hormone will elicit a specific response.
• Some hormones speed up the heart. Others
help digest food and allow the body to use the
food as fuel. Without hormones, humans
would not grow or mature.
• Hormones are essential to maintaining
homeostasis.
• Often, two or more hormones work together
to produce their effects.
• Hormones often last and affect you over
extended periods of time.
• The hypothalamus is part of the brain that
regulates body temperature, breathing,
hunger, and thirst. Besides being a part of the
nervous system, it is also the master
switchboard of the endocrine system. It
continually checks the conditions inside your
body. If your internal environment gets out of
balance, the hypothalamus can set everything
right again. It can even send out commands in
the form of a hormone.
• The pituitary gland produces at least six different
hormones in response to the hormones sent out by
the hypothalamus.
• Two of these hormones, growth hormone and
prolactin, have a direct effect on growth of bone and
cartilage.
• Feedback is a way the body will self-regulate. The
amount of hormones already in the body will affect
the endocrine system and either more or less of the
hormone depending on the body’s needs.
• A negative feedback will suppress the production of
more hormone. Most control is through negative
feedback because hormones are rarely turned off or
on completely.
• If you remember back to Chapter 4, the cell
has receptor proteins embedded in the cell
membrane. Each receptor has a unique
shape.
• When hormones approach a cell, the cell will
be able to respond to the hormone if the
shape of the receptor protein matches it.
• When the activity inside the cell changes, the
chemical reactions inside the cell also change.
Glands
• Adrenal glands – Two almond-shaped glands located
on the top of the kidneys.
– The adrenal medulla produces epinephrine or adrenaline.
This produces the “flight or fight” reaction. In a fraction of
a second, this hormone can be secreted in response to
fear, anger, pain or physical exertion.
– The adrenal cortex produces a hormone that helps the
body deal with long-term stress. It is a steroid called
cortisal. When stressful situations continue without relief,
the body enters a state of chronic fatigue. Organs
malfunction and physical as well as mental burnout may
result. Long term exposure to steroid hormones weakens
the immune system.
• Thyroid gland – located in the neck just below
the Adam’s apple.
– Thyroid hormones are necessary for normal
growth and development during childhood and
maintaining mental alertness in adults.
– Too much thyroxine causes Graves’ disease-people
have rapid, irregular heart rate, feel very nervous,
and lose weight. Treated with radioactive iodine.
– Low levels of thyroxine causes a condition that
combined with a lack of iodine produces a goiter.
• Pancreas – located under the liver
– Has cells that produce insulin that regulate how
much glucose is dissolved in the blood, called
blood sugar.
– Insulin plays a role in diabetes – a disease where
the person has an abnormally high blood sugar.
• Type I diabetes-usually childhood form, requires daily
injections of insulin.
• Type II diabetes-(95% of diabetics), usually occurs in
adult over 40. Obesity and inactivity contribute to its
development. Proper diet and exercise can improve it,
but sometimes oral medication is needed.