Download The Endocrine System

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The Endocrine System
Ebaa M Alzayadneh, DDS, PhD
Integrative Physiology and Pharmacology
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Overview of the endocrine
system
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Overview of the endocrine
system
Hormones are chemical messengers that are carried by the
bloodstream to different cells in the body.
 Hormones act at a distance from their place of production
directly on the target cell, inciting it to increase or decrease the
expression of specific genes.
Hormones can be either lipid-based, also known as steroidal,
or protein-based, known as non-steroidal.
Lipid hormones enter the target cell directly through the cell
membrane, and then travel to the nucleus and directly affect
expression of target genes. Protein hormones cannot enter the
cell, so they bind to receptors on the cell membrane, triggering
a secondary messenger system within the cell.
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Overview of the endocrine
system
Hormone release by the endocrine system is regulated
largely through negative feedback loops, and rarely
through positive feedback loops. In negative feedback,
increases in hormone activity lead to a decrease in the
production of that hormone.
Endocrine glands in turn have no duct and release their
secretions directly into the intercellular fluid or the blood.
The main endocrine glands are the pituitary (anterior and
posterior lobes), thyroid, parathyroid, adrenal (cortex and
medulla), pancreas and gonads.
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Nervous and Endocrine Systems:
Act together to coordinate functions of all body systems
Nervous system
• Responds to stimuli by sending
electrical action potentials along
neurons using neurotransmitters, the
chemical messenger of the nervous
system.
• This response to stimuli is near
instantaneous.
• The nervous system responds rapidly
to short-term changes by sending
electrical impulses.
• They may not last for long time
(briefer)
• Specific target
Endocrine system
• Hormones are synthesized at a
distance from their target cells, and
travel through the bloodstream or
intercellular fluid
• This process takes significantly longer
• effects are long lasting. Additionally,
target cells can respond to minute
quantities of hormones and are
sensitive to subtle changes in
hormone concentration.
• Broad spectrum of targets
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Endocrine Glands
• Glands are either:
• Secrete hormones into interstitial fluid, diffuse into blood
• Endocrine glands:
• Pituitary, thyroid, parathyroid, adrenal and pineal glands
• Hypothalamus, thymus, pancreas, ovaries, testes, kidneys,
stomach, liver, small intestine, skin, heart, adipose tissue,
and placenta not exclusively endocrine glands
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• Exocrine – have ducts
• Endocrine – ductless
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Hormone Activity
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• Hormones affect only specific target tissues with specific
receptors
• Receptors are constantly synthesized and broken down
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Hormones types
• Circulating – circulate in
blood throughout body
• Local hormones – act
locally
• Paracrine – act on
neighboring cells
• Autocrine – act on the
same cell that secreted
them
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• Lipid-soluble – use transport proteins
• Steroid
• Thyroid
• Nitric oxide (NO)
• Water-soluble – circulate in “free” form
• Amine
• Peptide/ protein
• Eicosanoid
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Chemical classes of hormones
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• Lipid-soluble – use transport proteins
• Steroid
• Thyroid
• Nitric oxide (NO)
• Water-soluble – circulate in “free” form
• Amine
• Peptide/ protein
• Eicosanoid
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Chemical classes of hormones
Chemical classes of hormones
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Chemical classes of hormones
• Response depends on both hormone and target cell
• Lipid-soluble hormones bind to receptors inside target cells
• Water-soluble hormones bind to receptors on the plasma membrane
• Activates second messenger system
• Amplification of original small signal
• Responsiveness of target cell depends on
• Hormone’s concentration
• Abundance of target cell receptors
• Influence exerted by other hormones:
• Permissiveness is the situation in which a hormone cannot exert its full effects without the presence
of another hormone.
• Synergism occurs when two or more hormones produce the same effects in a target cell and their
results are amplified.
• Antagonism occurs when a hormone opposes or reverses the effect of another hormone.
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Mechanisms of Hormone Action
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Blood capillary
1 Binding of hormone (first messenger)
to its receptor activates G protein,
which activates adenylate cyclase
Water-soluble
hormone
Adenylate cyclase
Receptor
Second messenger
G protein
ATP
cAMP
2 Activated adenylate
cyclase converts
ATP to cAMP
inactivates cAMP
3 cAMP serves as a
Activated
protein
kinases
second messenger
to activate protein
kinases
4 Activated protein
Protein
kinases
phosphorylate
cellular proteins
ATP
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6 Phosphodiesterase
Protein kinases
ADP
Protein—
P
5 Millions of phosphorylated
proteins cause reactions that
produce physiological responses
Water-soluble Hormones
Target cell
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Free hormone
Blood capillary
1 Lipid-soluble
hormone
diffuses into cell
2 Activated
Nucleus
Receptor
receptor-hormone
complex alters
gene expression
DNA
Cytosol
mRNA
3 Newly formed
mRNA directs
synthesis of
specific proteins
on ribosomes
Ribosome
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Transport
protein
New
protein
4 New proteins alter
cell's activity
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Lipid-soluble Hormones
Target cell
• Regulated by
• Signals from nervous
system
• Chemical changes in
the blood
• Other hormones
• Most hormonal
regulation by negative
feedback
• Few examples of
positive feedback
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Control of Hormone Secretion
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