Download Vertebrate Endocrine Systems

Animal Hormones
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Hormones and Their Actions
• In multicellular animals, nerve impulses provide
electric signals; hormones provide chemical
signals.
• Hormones work much more slowly than nerve
impulse transmission.
• Hormone-secreting cells are called endocrine
cells(내분비세포).
• Cells receiving the hormonal message are called
target cells and must have appropriate receptors.
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Hormones and Their Actions
• Hormones can be classified into three main groups:
 Peptides or proteins. They are water soluble and
transported by vesicles out of the cell that made
them.
 Steroid hormones are lipid-soluble and can
diffuse out of the cell that made them but in the
blood they must be bound to carrier proteins.
 Amine hormones are derivatives of the amino
acid tyrosine. Some are water-soluble and some
are lipid-soluble.
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• Some hormones act locally.
• Autocrine(자가분비)
hormones act on the
secreting cell itself.
• Paracrine(측분비)
hormones act on cells near
the site of release.
• Most hormones diffuse into
the blood, which distributes
them throughout the body.
Hormones and Their Actions
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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
• Some endocrine cells aggregate into secretory
organs called endocrine glands(내분비선).
• In vertebrates, nine major endocrine glands make
up the endocrine system.
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• The pituitary
gland(뇌하수체) of
mammals is a link
between the nervous
system and many
endocrine glands.
• The pituitary is made of
two parts: anterior and
posterior.
Vertebrate Endocrine Systems
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Vertebrate Endocrine Systems
• The posterior pituitary (뇌하수체 후엽) releases
two hormones: antidiuretic (항이뇨) hormone and
oxytocin.
• They are made by neurons in the hypothalamus,
are called neurohormones, 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.
• This movement of the vesicles is achieved by
kinesin proteins, powered by ATP, that “walk”
down the microtubules of the axon.
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Vertebrate Endocrine Systems
• The function of antidiuretic (항이뇨) hormone
(ADH) is to increase water conservation by the
kidney.
• If there is a high level of ADH secretion, the
kidneys resorb water.
• If there is a low level of ADH secretion, the kidneys
release water in dilute urine.
• ADH causes peripheral blood vessel constriction to
help elevate blood pressure and is also called
vasopressin.
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Vertebrate Endocrine Systems
• The function of oxytocin is to stimulate uterine
muscle contraction for the birth process.
• It also stimulates milk flow in the mother’s breasts.
Suckling by the baby, or even the sight or sound
of the baby, can cause the mother to secrete
oxytocin and release milk.
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Vertebrate Endocrine Systems
• The anterior pituitary(뇌하수체 전엽) releases
four tropic hormones(샘자극호르몬), which
control activities of other endocrine glands.
• They are peptide and protein hormones; each
is produced by a different type of pituitary cell.
• The four tropic hormones are:
thyrotropin(갑상선자극호르몬),
adrenocorticotropin(ACTH,부신피질자극호르
몬), luteinizing hormone(LH,
황체형성자극호르몬), and follicle-stimulating
hormone(FSH, 여포자극호르몬).
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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,
prolactin, melanocyte-stimulating
hormone, endorphins, and
enkephalins.
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Vertebrate Endocrine Systems
• Growth hormone (GH) acts on many tissues to
promote growth.
• GH stimulates cells to take up amino acids.
• GH also stimulates the liver to produce chemical
messages (insulin-like growth factors) that stimulate
bone and cartilage growth.
• Gigantism(거대증) is the result of overproduction of
GH in children.
• Underproduction of GH causes pituitary
dwarfism(뇌하수체성 왜소발육증). GH is now
produced by genetically engineered bacteria.
Figure 42.6 Effects of Excess Growth Hormone
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Vertebrate Endocrine Systems
• Prolactin stimulates the production and secretion
of milk in female mammals.
• Endorphins and enkephalins are the body’s
natural opiates(마취제). In the brain, these
molecules act as neurotransmitters in pain
pathways.
• The gene (one gene) encodes for a protein called
pro-opiomelanocortin.
• This large molecule is later cleaved into several
peptides including adrenocorticotropin,
melanocyte(흑색종)-stimulating hormone,
endorphins, and enkephalins.
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Vertebrate Endocrine Systems
• The anterior pituitary is
controlled by neurohormones
from the hypothalamus.
• The hypothalamus and the
anterior pituitary are
connected by portal blood
vessels(문맥혈관).
• Secretions from hypothalamic
nerves are transported by
these blood vessels to the
anterior pituitary.
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Vertebrate Endocrine Systems
• 1977, Nobel Prize
• Thyrotropin-releasing hormone
(TRH,갑상선자극호르몬) was the first releasing
hormone extracted from the hypothalamus.
• Gonadotropin-releasing hormone (GnRH,
생식선자극호르몬)
• Now many more hypothalamic neurohormones
are known.
Table 42.2 Releasing and Release-Inhibiting Neurohormones of the Hypothalamus
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Vertebrate Endocrine Systems
• The anterior pituitary cells are also
under negative feedback control by the
hormones of the glands that they
stimulate.
• For example, cortisol(5) is produced by
the adrenal gland (4) in response to
adrenocorticotropin(부신피질
자극호르몬) (3). It returns to the
pituitary(2) in the blood, and inhibits
further release of adrenocorticotropin.
• Cortisol also exerts negative feedback
control on the hypothalamus, inhibiting
release of adrenocorticotropinreleasing hormone (1).
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Figure 42.9 Hormonal Regulation of Calcium (Part 1)
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Vertebrate Endocrine Systems
• The thyroid gland(갑상선), located near the
trachea(기관), is an example of an endocrine gland.
• The thyroid gland produces the hormone thyroxine
in specialized structures.
• Two forms of thyroxine, T3 and T4, are made from
tyrosine. T3 (triiodothyronine) has three iodine
atoms. T4 has four iodine atoms.
• More T4 is produced, but it can be converted to T3
by an enzyme in the blood. T3 is the more active
form of the hormone.
In-Text Art p. 809(1)
In-Text Art p. 809(2)
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Vertebrate Endocrine Systems
• Thyroxine has many roles in regulating metabolism.
 It elevates metabolic rates in most cells and
tissues.
 It promotes amino acid uptake and protein
synthesis and so is critical for growth and
development. Insufficient thyroxine may result in
cretinism(크레틴병).
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Vertebrate Endocrine Systems
• A goiter(갑상선종) is an enlarged thyroid gland
associated with either very low
(hypothyroidism(갑상선기능저하증)) or very high
(hyperthyroidism(감상선기능항진증)) levels of
thyroxine.
• Hyperthyroid(갑상선항진) goiter results when the
negative feedback mechanism fails even though
blood levels of thyroxine are high.
• The thyroid remains maximally active and grows
larger, causing symptoms associated with high
metabolic rates (초조함, 신경질적, 흥분, 안구돌출).
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Vertebrate Endocrine Systems
• Hypothyroid(갑상선저하) goiter results when
there is insufficient thyroxine.
• The most common cause is a deficiency of dietary
iodine.
• The body symptoms of this condition are low
metabolism, cold intolerance, and physical and
mental sluggishness(무기력).
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Vertebrate Endocrine Systems
• Most calcium in the body is in the bones (99%).
About 1% is in the cells, and only 0.1% is in the
extracellular fluids.
• Blood calcium levels are regulated by:
 Deposition and absorption of bone
 Excretion of calcium by the kidneys
 Absorption of calcium from the digestive tract
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Vertebrate Endocrine Systems
• Calcitonin, released by the thyroid gland, acts to
lower calcium levels in the blood.
• Osteoclasts(파골세포) break down bone and
release calcium.
• Osteoblasts(조골세포) use circulating calcium to
build new bone.
• Calcitonin decreases osteoclast activity and
stimulates the osteoblasts to take up calcium for
bone growth.
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Vertebrate Endocrine Systems
• The four parathyroid glands(부갑상선) are
embedded in the posterior surface of the thyroid
gland.
• Blood calcium decrease triggers release of
parathyroid hormone (PTH), which in turn causes
the osteoclasts to dissolve bone and release
calcium.
• Parathyroid hormone also promotes calcium
resorption by the kidney to prevent loss in the urine.
• It also promotes vitamin D activation, which
stimulates the gut to absorb calcium from food.
• Parathyroid hormone and calcitonin act
antagonistically to regulate blood calcium levels.
Figure 42.9 Hormonal Regulation of Calcium (Part 1)
Figure 42.9 Hormonal Regulation of Calcium (Part 2)
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Vertebrate Endocrine Systems
• Diabetes mellitus(당뇨병) is a disease caused by
a lack of the protein hormone insulin or a lack of
insulin receptors on target cells.
• 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
• Insulin is produced in the pancreas in cell
clusters called islets of Langerhans
(랑게르한스섬).
• Several cell types have been identified in the
islets:
 Beta (b) cells produce and secrete insulin.
 Alpha (a) cells produce and secrete glucagon
(antagonist of insulin).
 Delta (d) cells produce somatostatin.
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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.
• If blood glucose falls too low, the a cells release
glucagon which stimulates the liver to convert
glycogen back to glucose.
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• The adrenal glands(부신) are
made up of the adrenal
medulla(부신수질) and the
adrenal cortex(부신피질).
• The medulla(수질) produces
epinephrine (adrenaline) and
norepinephrine.
• The cortex is under hormonal
control, mainly by
adrenocorticotropin (ACTH,
부신피질자극호르몬) from the
anterior pituitary.
Vertebrate Endocrine Systems
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Vertebrate Endocrine Systems
• The adrenal medulla produces epinephrine
(adrenaline) in response to stress, initiating fightor-flight reactions, such as increased heart and
breathing rates and elevated blood pressure.
• Epinephrine and norepinephrine are amine
hormones. They bind to two types of receptors in
target cells: a-adrenergic and b-adrenergic.
• Norepinephrine acts mostly on the alpha type, so
drugs called beta blockers, which inactivate only
b-adrenergic receptors, can be used to reduce
fight-or-flight responses to epinephrine.
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Vertebrate Endocrine Systems
• Adrenal cortex(부신피질) cells use cholesterol to
produce three classes of steroid hormones called
corticosteroids:
 Glucocorticoids influence blood glucose
concentrations.
 Mineralocorticoids influence extracellular
ionic balance.
 Sex steroids stimulate sexual development
and reproductive activity.
Figure 42.11 The Corticosteroid Hormones are Built from Cholesterol
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Vertebrate Endocrine Systems
• The main mineralocorticoid, aldosterone,
stimulates the kidney to conserve sodium and
excrete potassium.
• The main glucocorticoid, cortisol, mediates the
body’s response to stress.
• It also blocks the immune system reactions, which
temporarily are less critical.
• Cortisol can therefore be used to reduce
inflammation and allergy.
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Vertebrate Endocrine Systems
• The 생식소 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(태아)
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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• In mammals, the Y
chromosome causes the
gonads to start producing
androgens in the seven-weekold embryo, and the male
reproductive system develops.
• If androgens are not released,
the female reproductive
system develops.
Vertebrate Endocrine Systems
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Vertebrate Endocrine Systems
• Melatonin hormone is produced by the pineal
gland(송과선), located between the cerebral
hemispheres of the brain.
• Melatonin release occurs in the dark, marking the
length of night. Exposure to light inhibits
melatonin release.
• Melatonin is involved in biological rhythms,
including photoperiodicity(광주기성).
• In many animals, increasing day length signals
the onset of reproductive behavior.
Figure 42.13 The Release of Melatonin Regulates Seasonal Changes
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Hormone Actions:
The Role of Signal Transduction Pathways
• The length of time for the concentration of a
hormone to drop to one-half of the maximum is
called its half-life (반감기).
• Epinephrine’s half-life in the blood is only 1–3
minutes. Cortisol or thyroxine half-lives are on the
order of days.
• Half-life is partially determined by degradation and
elimination processes.
• Most hormones are broken down in the liver,
removed from the blood by the kidney, and excreted
in the urine.