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Endocrine System
Topic 16
I. Endocrine System
A. the endocrine system and nervous
system work together to coordinate the
activities of the body
 B. the endocrine system is a network of
glands and tissues that secrete
hormones which are chemical
messengers that are made in one place
and carried by the blood to act on
another part of the body
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C. compared to the nervous system, the signals of the
endocrine system take longer but will last longer
D. two types of hormones – steroid and peptide
hormones
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1. peptide hormones are large, hydrophilic, charged and
cannot diffuse across the plasma membrane – the receptors
for these hormones are found on the surface of the target cell
and causes it to transmit a signal into the cell’s interior – can
be used to turn on a protein kinase that phosphorylates
certain proteins and changes their activity – or they can be
used to release secondary messengers in the cell that amplify
the signal and alter cell activities – this type of indirect
signaling is called signal transduction cascade
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2. steroid hormones – small and
hydrophobic – most come from cholesterol,
including estrogen, progesterone,
testosterone, and cortisol – they can diffuse
through the cell membrane – these bind to
steroid hormone receptors after they have
diffused into the cell through the plasma
membrane – the receptors and hormones
enter the nucleus and bind to the target
regions in genes that regulate transcription
turning the genes on and off
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E. Endocrine glands
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1. hypothalamus – section of the posterior
forebrain – located above the pituitary gland
- releases hormone-like substances called
releasing factors into the anterior-pituitary
hypothalamic portal circulatory system
which triggers the anterior pituitary to
secrete the hormone indicated by the
releasing factor
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2. pituitary gland – small gland with two lobes lying
at the base of the brain – the two lobes (anterior
and posterior) function as independent glands
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(a) anterior pituitary gland
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(1) Growth horomone – growth of long bones
(2) thyroid stimulating hormone (TSH) – stimulates the
thyroid to secrete thyroxine
(3) adrenocorticotrophic hormone (ACTH) – stimulates the
adrenal cortex to secrete corticoids
(4) prolactin – responsible for milk production by the female
mammary glands
(5) follicle stimulating hormone – FSH – spurs the
maturation of seminiferous tubules in males and encourages
maturation of follicles in the ovaries
(6) luteinizing hormone – LH – induces the cells of the testes
to mature – in females, stimules ovulation
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(b) posterior pituitary
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(1) ADH – vasopressin – acts on the kidney to reduce
water loss
(2) oxytocin – acts on the uterus during birth to cause
uterine contraction
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3. thyroid gland – produces thyroxine ( a
modified amino acid) which accelerates
metabolism throughout the body – too little
thyroxine (hypothyroidism) causes goiter,
decreased heart rate, lethargy, obesity, and
decreased mental alertness – too much
thyroxine (hyperthyroidism) causes profuse
sweating, high body temperature, increased
metabolism, high blood pressure, loss of
weight, and irritability
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4. parathyroid glands – small – located on
the posterior surface of the thyroid – secrete
parathyroid hormone (parathormone) –
regulates the calcium and phosphate
balance between the blood, bone, and other
tissues – increased parathyroid hormone
increases bone formation
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5. pancreas – has an exocrine and an
endocrine function
(a) exocrine – secretes enzymes through ducts
into the small intestine
 (b) endocrine – secretes hormones into the
blood stream – islets of Langerhans – secrete
glucagon and insulin
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(1) insulin – stimulates cells to remove glucose from
the blood
(2) glucagon – stimulates the breakdown of glycogen
into glucose
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6. Adrenal glands – found on top of the kidneys –
made of the adrenal cortex and the adrenal medulla
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(a) adrenal cortex – responds to stress – ACTH stimulates
the adrenal cortex to synthesize and secrete the steroid
hormones known as corticosteroids
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(1) glucocorticoids – cortisol and cortisone – involved in
glucose regulation and protein metabolism, increase blood
glucose levels, reduces the body’s inflammatory responses
(2) mineralocorticoids – aldosterone – regulates plasma
levels of sodium and potassium – water volume
(3) androgens – male sex hormones
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(b) adrenal medulla – secret hormones into
circulatory system – produces epinephrine
(adrenaline) and norepinephrine (noradrenaline)
– both come from a class of amino acids called
catecholamines
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(1) epinephrine – increases glycogen to glucose in
liver and muscle tissue which causes a rise in blood
gluocse levels and an increase in metabolism
(2) norepinephrine – along with epinephrine, increase
the rate and strength of the heartbeat, and dilate and
constrict blood vessels which increases the blood
supply to skeletal muscle, the heart and brain – while
decreasing the blood supply to the kidneys, skin, and
digestive tract – this is the “fight or flight” response
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7. ovaries and testes
(a) testes – testosterone
 (b) ovaries – estrogen and progesterone
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How the endocrine system works
endocrine system
feedback mechanism
pancreas, insulin, and glucagon