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The Endocrine System
Endocrine system
Made of glands and their products
 Release products into the blood to deliver
messages to different parts of the body

Gland
Function
Chart
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Hormones
Chemicals released in one part of the body
that travel through the bloodstream to
affect other areas of the body
 Bind to specific receptors on target cells
 Full effect of hormones may take minutes,
hours, or days

Glands
Exocrine glands release their products
through ducts directly to organs that use
them; include glands that release sweat,
tears, and digestive juices
 Endocrine glands release their secretions
into the bloodstream

2 groups of hormones
Steroid hormones-are produced from a
lipid called cholesterol
 Nonsteroid hormones-include proteins,
small peptides, and amino acids
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Steroid hormones
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Can cross cell membranes easily, passing directly
across the lipid bilayer into the cytoplasm or the
nucleus
Binds a receptor-protein to make a hormonereceptor complex
Complex enters the nucleus and binds to DNA
Binding DNA initiates transcription of specific
genes to mRNA
mRNA moves to cytoplasm for translation into
proteins
Steroid hormones
Hormone-receptor complexes regulate
gene expression
 They can “turn on” or “turn off” whole
sets of genes
 Can produce dramatic changes in cell and
organism activity
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Nonsteroid hormones
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Cannot pass through the cell membrane
Must bind a receptor on the outside of the cell
membrane
Binding the receptor activates an enzyme on the
inside of the membrane
Enzyme activates secondary messengers (Ca2+
ions, cAMP, nucleotides, fatty acids) and carry
the message to the inside of the cell
Second messengers can alter other cell activities
Prostaglandins
Modified fatty acids
 Affect only nearby cells and tissues
 Cause smooth muscles to contract, such
as those in uterus, bronchioles, and blood
vessels
 Causes sensation of pain in most
headaches

Controlling metabolism
Metabolic activities are controlled by the
levels of thyroxine
 Thyroxin is released by the thyroid gland
 Thyroid gland is controlled by the
hypothalamus and anterior pituitary gland
 Hypothalamus senses a low level of
thyroxine in blood, it secretes thyroidreleasing hormone (TRH)
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Controlling metabolism cont
TRH stimulates anterior pituitary to
secrete thyroid-stimulating hormone (TSH)
 TSH stimulates the release of thyroxine by
the thyroid gland
 High levels of thyroxine in the blood inhibit
the secretion of TRH and TSH and stops
additional release of thyroxine

Body temperature
Also controlled by hypothalamus
 Since increased metabolic rates raise body
temperature
 If low body temperature is sensed by the
hypothalamus, TRH and TSH will be
released to stimulate release of thyroxine
 Thyroxin increases metabolism and thus
increases or raises body temperature

Maintaining water balance
Hypothalamus is sensitive to water levels in the
blood
 Loss of water raises the concentration of
dissolved materials in blood and signals the
hypothalamus to stimulate the pituitary to
release ADH (antidiuretic hormone)
 ADH travels to kidneys to slow down removal of
water and triggers sensation of thirst
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Water balance cont
Water is quickly absorbed when consumed
 When water levels in blood increase, the
pituitary releases LESS ADH so the kidneys
can remove more water
 This restores the blood to its normal
concentration
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Sleep cycle
Controlled through the pineal gland by
influencing the pituitary gland and
producing the hormone melatonin
 Pineal gland’s functioning is initiated by
the amount of light in a 24 hour period
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Complimentary hormone action
Used to regulate calcium levels in the
bloodstream
 Blood Ca2+ levels get too high, thyroid gland
releases calcitonin so kidneys reabsorb less
calcium, less calcium is absorbed in intestines
and MORE calcium is deposited in bones
 Blood Ca2+ levels get too low, parathyroid
hormone (PTH) is released from parathyroid
glands so kidneys reabsorb more Ca2+, intestines
absorb more Ca2+, and bones release Ca2+ into
blood
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PTH Hormones
Diagram
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Importance of Calcium

If calcium levels in blood drop below a
normal range:
 Blood
doesn’t clot
 Muscles don’t contract
 Transport of materials across cell membranes
will fail
Pituitary gland
Is divided into two parts: anterior pituitary
and posterior pituitary
 Secretes 9 hormones that directly regulate
body functions and controls actions of
other endocrine glands
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Posterior pituitary
Antidiuretic hormone (ADH)-stimulates
kidneys to reabsorb water from collecting
tubules
 Oxytocin-stimulates contractions of uterus
during birth; releases milk in nursing
mothers
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Posterior pituitary
Follicle-stimulating hormone (FSH)stimulates production of mature eggs and
sperm
 Luteinizing hormone (LH)-stimulates
ovaries and testes; prepares uterus for
implantation of fertilized egg
 Thyroid-stimulating hormone (TSH)stimulates the synthesis and release of
thyroxine from the thyroid gland
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Posterior pituitary cont.
Adreno-corticotropic hormone (ACTH)-stimulates
release of some hormones from the adrenal
cortex, mainly cortisol (overproduction of which
causes Cushing’s disease)
 Growth hormone (GH)-stimulates protein
synthesis and growth in cells
 Prolactin-stimulates milk production in nursing
mothers
 Melanocyte-stimulating hormone (MSH)stimulates the melanocytes of the skin,
increasing their production of the skin pigment
melanin
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hGH
Hormone
diagram
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Hypothalamus
Controls secretions of pituitary gland
 Influenced by hormone levels in the blood
and sensory information received from
nervous system
 Posterior pituitary made of axons whose
cell bodies are in the hypothalamus
 When cell bodies are stimulated, axons of
posterior pituitary release their hormones
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Hypothalamus cont
Indirect affect on anterior pituitary
 Hypothalamus produces releasing
hormones in the blood that are carried to
anterior pituitary to control production and
release of hormones
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Thyroid gland
Major role in regulating metabolism
 Produces thyroxine to increase the rate of
protein, carbohydrate, and fat metabolism
 Thyroxine also increases rate of cellular
respiration and the amount of energy and
heat released
 Decreased levels of thyroxine decrease the
rate of cellular respiration and the amount
of energy and heat released
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Hyperthyroidism
Caused by too much thyroxine
 Results in nervousness, elevated body
temperature, increased metabolic rate,
increased blood pressure, and weight loss

Hypothyroidism
Caused by too little thyroxine
 Results in lower metabolic rates, lower
body temperature, lack of energy, and
weight gain
 Can cause a goiter (enlargement of the
thyroid gland)
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Parathyroid glands
Four
 Help control calcium levels in blood
 Promote proper nerve and muscle function
and bone structure
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Adrenal glands
Located on top of kidneys
 Release hormones that help body prepare
for and deal with stress
 Outer part is adrenal cortex; inner part is
adrenal medulla
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Adrenal cortex
80% of adrenal gland
 Produces over 24 corticosteroid hormones
 Aldosterone-regulates reabsorption of
sodium ions and excretion of potassium
ions by kidneys
 Cortisol-helps control rate of metabolism
of carbohydrates, fats, and proteins
 Over-production of cortisol can lead to
Cushing’s disease
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Adrenal medulla
Regulated by sympathetic nervous system
 Prepares body for energy-intense activities
 Epinephrine (80% of total secretions from
adrenal medulla) and norepinephrine
 Fight or flight response
 Increase heart rate, blood pressure, blood
flow to muscles, open air passages,
release extra glucose into blood, increases
body activity
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Adrenal gland
Also responsible for causing posttraumatic stress syndrome (PTSS)
 Release of some hormones from adrenal
gland causes the person to re-experience
a traumatic event
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Pancreas
Acts as an exocrine gland by releasing
secretions through ducts to intestine to
help break down food
 Acts as an endocrine gland by releasing
hormones into the blood
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Pancreas (endocrine function)
Hormones released from islets of Langerhans
 Each islet has beta cells that release insulin and
alpha cells that release glucagon
 Insulin stimulates liver and muscles to remove
sugar from the blood and store it as glycogen or
fat
 Glucagon stimulates the liver to break down
glycogen and release glucose back into the
blood and the release of fatty acids from stored
fats
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Pancreas
& Liver
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Reproductive glands
Gonads produce gametes and secrete sex
hormones
 Female gonads are ovaries and produce
eggs (ova)
 Male gonads are testes and produce
sperm
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Ovaries
Estrogen-female sex hormone; required
for development of eggs and formation of
physical traits associated with female body
 Progesterone-prepares uterus for arrival of
developing embryo
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Testes
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Produce testosterone
 Required
for normal sperm production
 Development of physical traits associated with
male body