Download Chapter 2 The Vertebrate Endocrine System

Chapter 1
The Vertebrate Endocrine System
Nam Deuk Kim, Ph.D.
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Contents
1. Endocrine glands and
their hormones
2. Hormones defined
3. General classes of
chemical messengers
4. Hormone synthesis
5. Control of hormone
secretion
6. Hormone delivery
7. Hormone circulation and
metabolism
8. Physiological roles of
hormones
9. General mechanisms of
hormone action
10. Endocrine
pathophysiology
11. Comparative
endocrinology
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1. Endocrine glands and their hormones
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2. Hormones defined
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3. General classes of chemical messengers
(such as hormones)
• Endocrinology
– Study of homeostatic activities accomplished by
hormones
• Two distinct groups of hormones based on
their solubility properties
– Hydrophilic hormones
• Highly water soluble
• Low lipid solubility
– Lipophilic hormones
• High lipid solubility
• Poorly soluble in water
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1) Protein hormones comprise the
most diverse family of chemical
messengers.
2) The thyroid gland produces
iodine-containing hormones,
thyroxine and triiodothyronine
(T3).
3) Steroid hormones are produced
primarily by the adrenal cortex
(e.g., such as cortisol,
corticosterone, and aldosterone,
and gonads (e.g., testosterone,
estradiol, and progesterone).
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4) Many neurotransmitters are enzymatically modified amino acids
- acetylcholine, norepinephrine, dopamine, serotonin (5hydroxytryptamine, 5-HT), gamma-aminobutyric acid (GABA), and
glutamate
5) Neuropeptides can function as neurohormones, neurotransmitters, and
neuromodulators.
6) Growth factors are a diverse group of locally acting peptide messengers
- nerve growth factor, brain-derived neurotrophic factor (BDNF),
neurotrophin-3 (NT-3), transforming growth factor β (TGF β), bone
morphogenetic protein (BMPs), erythropoietin (erythrocyte-stimulating
factor), epidermal growth factor (EGF), fibroblast growth factor (FGF)
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7) Eicosanoids are fatty acid derivatives that include prostaglandins,
thromboxanes, and leukotrienes
Arachidonic Acid Metabolites
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8) Pheromones are a diverse group of chemical messengers that
mediate signaling between individuals.
- Bombykol: invertebrate pheromone from the silkworm moth
- Civetone: vertebrate pheromone from the civet (사향고양이)
9) Electrolytes and metabolites can also convey physiological signals.
- hydrogen ion, sodium ion, calcium, glucose, certain amino acids
(arginine, glutamate, and glycine)
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4. Hormone synthesis
1) Protein hormone
synthesis involves
DND transcription,
mRNA translation,
and prohormone
processing
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2) Steroid hormones
are derived from
cholesterol.
(DHEA)
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3) Thyroid
hormone
synthesis
requires a
unique series
of
biochemical
processes in
follicular
cells.
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4) Non-peptide
neurotransmitters
are synthesized in
nerve endings.
- Acetylcholine
- Dopamine
- Norepinephrine
- Epinephrine
- Serotonin
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5) Gases can function as
chemical messengers
- Nitric oxide (NO) 
nitric oxide synthase
(NOS)  cGMP
induction  relaxation
of the smooth muscle
cell and vasodilation
Functions of Nitric Oxide (NO)
- Carbon monoxide (CO)
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6) Peptide neurohormones and neurotransmitters are
synthesized in the same manner as protein hormones
7) Some peptide and steroid hormones are derived from
prohormones after secretion
- Preproenzyme (i.e., insulin)
- Post-translational processing
- Endopeptidases
- RAAS (renin-angiotensin-aldostreone system)
- Conversion of testosterone to dihydrotestosterone by
5α-reductase
- Conversion of testosterone to estradiol by aromatase
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5. Control of hormone section
1) Hormone secretion can be a regulated or constitutive
process
- Regulated process: Ca2+-dependent exocytosis
- Constitutive process: passive diffusion
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2) Secretion of one hormone
is often controlled by the
actions of another
3) Secretions of some
hormones are controlled by
the ionic, metabolic or
hormonal factors they
regulate.
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6. Hormone delivery
1)
2)
3)
4)
5)
Endocrine:
Neuroendocrine:
Paracrine:
Neurocrine:
Lumonal: released into the lumen of the gut
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7. Hormone circulation and metabolism
1) Peptide hormones have short half-lives in the
circulation
- shorter peptide hormones: t½ = 2 ~ 30 min
- TSH: t½ = 60 min
- Exopeptidases: carboxypeptidase, aminopeptidase
- Endopeptidase
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Fig. 2.8. Model of peptide degradation by proteolytic enzymes
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Activation of Insulin
 Preproinsulin: 110 amino acids
 Active insulin: 51 amino acids
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2) Steroid and thyroid hormone are bound by globulins that
increases their half-lives
- Steroid hormone binding proteins and albumin
- Metabolized steroid hormones: by sulfation and glucuronide
conjugation
Fig. 2.9. Steroid hormone sulfation and glucuronide formation
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3) Adrenal catecholamines and neurotransmitters are
enzymatically inactived in liver and brain, respectively.
- The metabolism of circulating catecholamines occurs
mainly in the liver by orthomethylation and oxidative
deamination by catechol O-methyltransferase (COMT) and
monoamine oxidase (MAO), respectively.
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8. Physiological roles of hormones
1) Affect cellular synthesis and secretion of other
biologically active molecules
2) Affect metabolic processes, both anabolic and
catabolic, in most cells
3) Affect contraction, relaxation, and metabolism of
muscle
4) Control reproductive processes
5) Stimulate or inhibit cellular proliferation
6) Regulate excretion and reabsorption of inorganic
cations and anions from the kidney
7) Have permissive actions
8) Play important roles in animal behavior
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9. General mechanisms of hormone action
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10. Endocrine pathophysiology
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11. Comparative endocrinology
1) Human
2) Mammals: rats and mice
3) Nonmammalian forms:
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