Download Vertebrate Endocrine Systems

Animal Hormones
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Introduction
• Chemical messages, or hormones, produce and
coordinate anatomical, physiological, and
behavioral changes in an animal.
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Hormones and Their Actions
• Control and regulation require information.
• In multicellular animals, hormones provide
chemical signals.
• Hormones are secreted by cells, diffuse into the
extracellular fluid, and often are distributed by the
circulatory system.
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Hormones and Their Actions
• Hormone-secreting cells are called endocrine
cells.
• Cells receiving the hormonal message are called
target cells and must have appropriate receptors.
• The binding of the receptor activates a response.
• The distance over which the signal operates
distinguishes hormone groups; some act close to
the release site, others at distant body locations.
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Hormones and Their Actions
• Hormones can be classified into three main groups:
 Peptides or proteins: water soluble,
transported by vesicles out of the cell that made
them.
 Steroids: lipid-soluble, diffuse out of the cell that
made them but in the blood they must be bound
to carrier proteins.
 Amine: derivatives of the amino acid tyrosine;
water-soluble and lipid-soluble.
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Hormones and Their Actions
• Some hormones act on distant cells – these get into the
circulatory system.
• Some hormones act locally – these never get into the
circulatory system.
 Autocrine hormones act on the secreting cell itself.
 Paracrine hormones act on cells near the site of
release.
 released in tiny amounts
 are inactivated rapidly by enzymes
 are taken up efficiently by local cells.
Figure 42.1 Chemical Signaling Systems
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Hormones and Their Actions
• Most hormones diffuse into the blood, which
distributes them throughout the body.
• When the hormone message encounters a cell with
the proper receptor, it binds and triggers a
response.
• The same hormone can cause different responses
in different types of cells.
• An example is epinephrine. The nervous system
reacts to an emergency very quickly and stimulates
adrenal cells to secrete epinephrine. The result is
the fight-or-flight response.
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Hormones and Their Actions
• The epinephrine acts on different cells in the body:
 In the heart, it stimulates faster and stronger
heartbeat.
 Blood vessels in some areas constrict to send
more blood to muscles.
 In the liver, glycogen is broken down to glucose
to provide quick energy.
 In fat tissue, fats are mobilized as another
energy source.
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Hormones and Their Actions
• Endocrine refers to cells or glands that do not
have ducts leading to the outside of the body;
they secrete their products directly into the
extracellular fluid.
• Some endocrine cells are single cells within a
tissue.
• Some endocrine cells aggregate into secretory
organs called endocrine glands.
• In vertebrates, nine major endocrine glands make
up the endocrine system.
Figure 42.2 The Endocrine System of Humans
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Vertebrate Endocrine Systems
• The pituitary gland of mammals is a
link between the nervous system
and many endocrine glands and
plays a crucial role in the endocrine
system.
The Pituitary Gland
• The pituitary gland sits in a
depression at the bottom of the skull
and is attached to the hypothalamus.
• The pituitary is made of two parts:
anterior and posterior.
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Vertebrate Endocrine Systems
• The posterior pituitary
releases two hormones:
antidiuretic hormone and
oxytocin.
• They are made by
neurons in the
hypothalamus, and are
packaged in vesicles.
• The vesicles are
transported down the
axons of the neurons that
made them and are
stored in the posterior
pituitary.
- The function of antidiuretic
hormone (ADH) is to increase water
conservation by the kidney.
- The function of oxytocin is to
stimulate uterine muscle contraction for
the birth process.
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Vertebrate Endocrine Systems
• The Anterior Pituitary releases
four tropic hormones, which
control activities of other
endocrine glands.
• The four tropic hormones are:
 thyrotropin (stimulates the
thyroid gland)
 adrenocorticotropin
 luteinizing hormone
 follicle-stimulating hormone.
Anterior lobe of the human
pituitary gland.
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Vertebrate Endocrine Systems
• Other peptide and protein anterior pituitary
hormones influence tissues that are not endocrine
glands.
• These include:
 growth hormone (acts on many tissues to
promote growth)
 prolactin (stimulates the production and
secretion of milk in female mammals)
 melanocyte-stimulating hormone
 endorphins, enkephalins (molecules that act
as neurotransmitters in pain pathways)
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• The anterior pituitary is
controlled by
neurohormones from the
hypothalamus.
• The hypothalamus obtains
data about body conditions
and the external
environment through both
neuronal and hormonal
signals.
• Secretions from
hypothalamic nerves are
transported by blood vessels
to the anterior pituitary.
Vertebrate Endocrine Systems
Figure 42.8 Multiple Feedback Loops Control Hormone Secretion
The anterior
pituitary cells are
also under negative
feedback control
by the hormones of
the glands that they
stimulate.
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Vertebrate Endocrine Systems
• The thyroid gland, located near the trachea, is an
example of an endocrine gland that is controlled by
negative feedback.
• The thyroid gland produces the hormone thyroxine
in specialized structures called follicles.
• Thyroxine has many roles in regulating metabolism.
Thyroid and parathyroid
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Vertebrate Endocrine Systems
• The four parathyroid glands are embedded in the posterior
surface of the thyroid gland.
• It is important in regulating blood calcium levels:
 Low blood calcium = release of parathyroid hormone
 causes specialized cells to dissolve bone and release
calcium
 promotes calcium resorption by the kidney to prevent
loss in the urine
 promotes vitamin D (actually a hormone) activation,
which stimulates the gut to absorb calcium from food.
 High blood calcium = release of calcitonin
 lower calcium levels in the blood.
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Vertebrate Endocrine Systems
• Diabetes mellitus is a disease caused by a lack
of the protein hormone insulin (Type I) or a lack
of insulin receptors on target cells (Type II).
• Insulin binds to receptors on the cell membrane
and allows glucose uptake.
• Without insulin or the receptors, glucose
accumulates in the blood until it is lost in urine.
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Vertebrate Endocrine Systems
• High glucose levels in the blood cause water to
move from the cells into the blood by osmosis.
• The kidneys then increase urine output to get rid
of the fluid excess.
• Cells not taking up glucose use fat and protein for
fuel, resulting in the body’s wasting away and
tissue and organ damage.
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Vertebrate Endocrine Systems
• Insulin is produced in
the pancreas in cell
clusters called islets
of Langerhans.
• The remainder of the
pancreas acts as an
exocrine gland with
digestive functions.
Human Pancreatic Islet
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Vertebrate Endocrine Systems
• After a meal, blood glucose levels rise and
stimulate the b cells to release insulin.
• Insulin stimulates cells to use glucose and to
convert it to glycogen and fat.
• When blood glucose levels fall, the pancreas
stops releasing insulin, and cells switch to using
glycogen and fat for energy.
• If blood glucose falls too low, the cells release
glucagon which stimulates the liver to convert
glycogen back to glucose.
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Vertebrate Endocrine Systems
• The adrenal glands are made up of the adrenal medulla
and the adrenal cortex.
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Vertebrate Endocrine Systems
• The medulla produces:
 epinephrine (response
to stress, initiating fightor-flight reactions increased heart, breathing
rates, elevated blood
pressure)
 norepinephrine (a
neurotransmitter involved
in physiological
regulation)
Adrenal medulla
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Vertebrate Endocrine Systems
• Adrenal cortex cells use cholesterol to
produce three classes of steroid hormones
called corticosteroids:
 Glucocorticoids influence blood glucose
concentrations and other aspects of fuel
molecule metabolism.
Human adrenal gland
 Mineralocorticoids influence extracellular
ionic balance.
 Sex steroids stimulate sexual
development and reproductive activity.
These are secreted in only minimal
amounts by the adrenal cortex.
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Vertebrate Endocrine Systems
• The gonads (testes and ovaries) produce steroid
hormones synthesized from cholesterol.
• Androgens are male steroids, the dominant one
being testosterone.
• Estrogens and progesterone are female
steroids, the dominant estrogen being estradiol.
• Sex steroids determine whether a fetus develops
into a male or female.
• After birth, sex steroids control maturation of sex
organs and secondary sex characteristics such as
breasts and facial hair.
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Vertebrate Endocrine Systems
• Sex steroid production increases rapidly at
puberty, or sexual maturation, in humans.
• Control of sex steroids (both male and female) is
under the anterior pituitary tropic hormones called
luteinizing hormone (LH) and follicle-stimulating
hormone (FSH).
• These gonadotropins are controlled by the
hypothalamus.
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Vertebrate Endocrine Systems
• Synthetic androgens (anabolic steroids) can
exaggerate body strength and muscle
development.
• Negative side effects in females include more
masculine body features, such as shrinking the
uterus and causing an irregular menstrual cycle.
• In males, the negative side effects include
shrinking of the testes, enlarged breasts, and
sterility.
• Continued use of anabolic steroids may increase
risk of heart disease, some cancers, kidney
damage, and personality disorders.