Biology
Chapter 39
The Endocrine System
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What is the
function of the
endocrine
system?
To release hormones,
which send messages
throughout the body
via the blood stream.
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What are
hormones?
Chemicals made &
released in one part of the
body that affect the cells
in OTHER parts of the
body.
Organs called GLANDS
make hormones
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What do
hormones
do?
Hormones bind to specific
receptors on their TARGET
cells.
This changes the activity
of the target cells.
The effect can last from
minutes to days.
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39-1
Cells that have receptors for a particular
hormone are called
a. nerve cells.
b. target cells.
c. exocrine cells.
d. endocrine cells.
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39-1
Chemicals that travel through the bloodstream
and affect the activities of other cells are known
as
a. hormones.
b. receptors.
c. enzymes.
d. messengers.
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39-1 The Endocrine System
Glands
DO NOT WRITE
ANYTHING. JUST READ
Hypothalamus
The hypothalamus makes
hormones that control the
pituitary gland. In addition,
the hypothalamus makes
hormones that are stored
in the pituitary gland.
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39-1 The Endocrine System
Glands
Pituitary gland
The pituitary gland
produces hormones that
regulate many of the other
endocrine glands.
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39-1 The Endocrine System
Glands
Parathyroid glands
The parathyroid glands
release parathyroid
hormone, which regulates
the level of calcium in the
blood.
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39-1 The Endocrine System
Glands
Thymus
During childhood, the
thymus releases thymosin,
which stimulates T cell
development and proper
immune response.
This is important. Write it
down.
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39-1 The Endocrine System
Glands
Adrenal glands
The adrenal glands
release adrenaline and
norepinephrine, which
help the body respond to
stress. (Fight or flight
response) Know this
one.
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39-1 The Endocrine System
Glands
Testis
The testes produce
testosterone, which is
responsible for sperm
production and the
development of male
secondary sex
characteristics.
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39-1 The Endocrine System
Glands
Ovary
Ovaries produce estrogen
and progesterone. Estrogen
is required for the
development of female
secondary sex characteristics
and for the development of
eggs. Progesterone prepares
the uterus for a fertilized egg.
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39-1 The Endocrine System
Glands
Pancreas
The pancreas produces
insulin and glucagon,
which regulate the level
of glucose in the blood.
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39-1 The Endocrine System
Glands
Thyroid
The thyroid produces
thyroxine, which regulates
metabolism throughout the
body.
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39-1 The Endocrine System
Glands
Pineal gland
The pineal gland releases
melatonin, which is
involved in rhythmic
activities, such as daily
sleep-wake cycles.
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39-1 The Endocrine System
How are
hormones
classified?
Some are STEROID
hormones made from a
lipid (fat) called cholesterol
Steroid hormones can
cross cell membranes
easily.
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39-1 The Endocrine System
The Endocrine System
Steroid Hormone Action
Steroid hormone
Receptor
Nucleus
Hormone-receptor
complex: notice this
directly affects gene
expression.
Altered cellular
function
DNA
Protein
synthesis
mRNA
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39-1 The Endocrine System
A steroid hormone
enters a cell directly
across its membrane.
The Endocrine System
Steroid hormone
It binds to a receptor
to form a hormonereceptor complex.
Receptor
Hormone-receptor
complex
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39-1 The Endocrine System
The Endocrine System
The hormone-receptor
complex enters the
nucleus, where it binds
to a DNA control
sequence.
Binding initiates
transcription of genes to
mRNA.
DNA
Nucleus
mRNA
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39-1 The Endocrine System
The Endocrine System
mRNA moves into the cytoplasm to direct protein
synthesis.
Altered cellular
function
Protein
synthesis
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39-1 The Endocrine System
How are
hormones
classified?
Hormone Action
There are also nonsteroid
hormones which include
proteins, small peptides
and modified amino
acids.
Nonsteroid hormones
CANNOT pass through
the cell membrane.
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39-1 The Endocrine System
The Endocrine System
Nonsteroid hormone
(first messenger)
A nonsteroid
hormone binds to
receptors ON THE
CELL MEMBRANE.
This activates an
enzyme on the
inside of the
membrane.
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39-1 The Endocrine System
The Endocrine System
This enzyme
activates secondary
messengers that
carry the message of
the hormone inside
the cell.
These messengers
activate and inhibit
many cell activities.
ATP
cAMP
(second messenger)
Enzyme
activities
Altered
cellular
function
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39-1 The Endocrine System
How does the
endocrine
system maintain
homeostasis?
The endocrine system is
regulated by FEEDBACK
mechanisms that
function to maintain
homeostasis.
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39-1 The Endocrine System
What is an
example of
feedback
regulation
Control of the Endocrine System
The control of the metabolic
rate of your cells.
• Thyroxine (made by thyroid
gland) increases metabolic
rate.
• Probably affects ALL cells
of the body!
• Important for growth &
development.
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Problems:
1. How will the body know it should
make more thyroxine?
2. How will it know when it has made
enough thyroxine?
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39-1 The Endocrine System
Control of the Endocrine System
Book’s explanation (a bit much):
If thyroxine is low, the hypothalamus secretes
thyrotropin-releasing hormone (TRH), which
stimulates the anterior pituitary to secrete thyroidstimulating hormone (TSH).
TSH stimulates the release of thyroxine.
High levels of thyroxine in the blood inhibit secretion
of TRH and TSH, which stops the release of
additional thyroxine.
!!!!!
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39-1 The Endocrine System
Negative feedback =
the output of a
pathway inhibits the
inputs to the pathway.
The end product
shuts off the
pathway that
makes that
product.
T3 & T4 are forms of
thyroxine
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39-1 The Endocrine System
1
Control of the Endocrine System
7
Controlling
Metabolism 2
3
Don’t write
all of this
but DO
recognize
the negative
feedback
loop.
4
5
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39-1
Which group of hormones act on target cells by
binding directly to DNA in the nucleus?
a. steroids
b. nonsteroids
c. proteins
d. second messengers
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39-1
Metabolism is maintained by feedback loops
involving the
a. hypothalamus, gonads, and adrenal glands.
b. hypothalamus, anterior pituitary, and thyroid
gland.
c. anterior pituitary, pancreas, and thyroid
gland.
d. thyroid gland, parathyroid gland, and
pancreas.
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39-1 The Endocrine System
What is the
function of
the pancreas?
A digestive gland whose
secretions help break
down food.
Also an endocrine gland which
makes INSULIN & GLUCAGON
These regulate levels of
blood sugar, glucose!
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39-1 The Endocrine System
First, remember that foods you
eat are broken down and
converted to glucose (sugar)
What does the
hormone
INSULIN do?
Insulin: stimulates cells in muscle
& liver to REMOVE glucose from
bloodstream
• Glucose is then used right
away to make ATP
• OR liver converts and stores
it (short-term) as glycogen
• OR gets converted & stored
(long-term) as fat
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What does the
opposite
hormone,
GLUCAGON
do?
Remember that glycogen: a SHORT
term storage form of glucose
Glucagon: stimulates cells in liver
to change glycogen back into
glucose and return it to
bloodstream when you need it.
Now the glucose is available as
fuel to create ATP.
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39-1 The Endocrine System
What is
diabetes?
Show Mayo
Clinic video
clip.
Type I: an autoimmune disease
in which person does not
produce insulin.
Type II: a lifestyle disease
resulting from obesity. The
body makes insulin but the
cells are resistant to it.
(also gestational
diabetes = only
during pregnancy)
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39-2
Diabetes mellitus is a disease that results when
the pancreas fails to produce or properly use
a. glucose.
b. insulin.
c. glucagon.
d. carbohydrate.
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39-2
Metabolism is regulated by
a. thyroxine.
b. parathyroid hormone.
c. epinephrine.
d. estrogen.
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39-2
The gonads are the body's
a. target cells.
b. exocrine glands.
c. reproductive glands.
d. reproductive cells.
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39-2
Adrenaline (AKA epinephrine) is a hormone
produced by the adrenal medulla and is
responsible for
a. the “fight or flight” response to stress.
b. controlling the level of insulin in the blood.
c. maintaining proper levels of sodium and
potassium in the blood.
d. regulating the water content of the body.
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