Transcript Document

The Endocrine System
Types of Chemical Messengers
A hormone is a chemical that is secreted into
extracellular fluid and carried by the blood
-Can therefore act at a distance from source
-Only targets with receptor can respond
Paracrine regulators do not travel in blood
-Allow cells of organ to regulate each other
Pheromones are chemicals released into the
environment to communicate among
individuals of a single species
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Endocrine System
The endocrine system
includes all the organs and
tissues that produce
hormones
 Includes endocrine
glands, which are
specialized to secrete
hormones
 Also organs, like the liver,
that secrete hormones in
addition to other functions
Exocrine glands secrete
their products, such as
saliva or milk, into a duct
for transport to the outside
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Feedback Mechanisms

For hormone
secretion regulated
by the negative
feedback loop: when
gland X releases
hormone X, this
stimulates target
cells to release
hormone Y. When
there is an excess of
hormone Y, gland X
"senses" this and
inhibits its release of
hormone X.
Cooperative Learning

Get in groups of 4 and assign the
following 4 roles—scribe, task manager,
researcher, organizer.
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
Task 1. Differentiate between hormones
and paracrine regulators. What are
examples of each? What are the classes of
endocrine glands and give examples.
Discuss the differences between lipophilic
and hydrophilic hormones AND discuss in
detail, with drawings, the method of
action for each group.
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
Task 2. Describe the location and
composition of the pituitary gland. List the
two divisions of it and name the hormones
produced by each division and their
activity. Describe the role, in words and
pictures, of the Hypothalamus (one great
way to do this would be to make a flow
chart or concept map) and pituitary.
Include in your drawing or description
how feedback from other glands affects
the hypothalamus and pituitary.
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
Task 3. List the peripheral endocrine
glands and their functions. Mention the
“other” hormones and their effects.
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Types of Chemical Messengers
Some neurotransmitters
are distributed by the
blood and act as
neurohormones
-Norepinephrine
coordinates the activity
of heart, liver and blood
vessels during stress
Hormone production and
release is often
regulated directly or
indirectly by the
nervous system
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Classes of Hormones
Molecules that function as hormones must
exhibit two basic characteristics
1. Must be sufficiently complex to convey
regulatory information to their target cells
2. Must be adequately stable to resist
destruction before reaching their target cells
Three chemical classes meet these
requirements
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Classes of Hormones
1. Peptides and proteins
-Glycoproteins
2. Amino acid derivatives
-Catecholamines
-Thyroid hormones
-Melatonin
3. Steroids
-Sex steroids
-Corticosteroids
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Classes of Hormones
Hormones may be categorized as:
-Lipophilic (nonpolar) = fat-soluble
-Steroid hormones and thyroid hormones
-Bind to intracellular receptors
-Hydrophilic (polar) = water-soluble
-All other hormones
-Bind to extracellular receptors
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Lipophilic Hormones
Lipophilic hormones include the steroid
hormones (derived from cholesterol) and
the thyroid hormones (tyrosine + iodine)
-As well as the retinoids, or vitamin A
Testosterone
Cortisol (Hydrocortisone)
CH2OH
HO
H3C
C O
H3C
OH
H3C
H3C
Thyroxine
OH
I
HO
COOH
CH2 CH
O
I
O
I
I
NH2
O
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Lipophilic Hormones
These hormones circulate in the blood bound
to transport proteins
-Dissociate from carrier at target cells
-Pass through the cell membrane and
bind to an intracellular receptor, either in
the cytoplasm or the nucleus
-Hormone-receptor complex binds to
hormone response elements in DNA
-Regulate gene expression
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1. Hormone passes
Blood
plasma
through plasma
membrane
Lipophilic hormones
Plasma membrane
Cytoplasm
Nucleus
2. Inside target
Receptor
cell the hormone
binds to a
receptor protein
in the cytoplasm
or nucleus
3. Hormone-receptor
complex binds to
hormone response
element on DNA,
regulating gene
transcription
5. Change in protein
synthesis is
cellular response
mRNA
Protein
DNA
4. Protein synthesis
Hormone response element
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Hydrophilic Hormones
Hydrophilic hormones include the peptide,
protein and catecholamine hormones
-Too large or polar to cross cell membrane
Hormones bind to extracellular receptors
-Initiate signal transduction pathways
1. Activation of protein kinases
2. Production of second messengers
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Hydrophilic Hormones
Receptor kinases
 For some peptide hormones (like insulin)
the receptor itself is a kinase


Can directly phosphorylate intracellular
proteins that alter cellular activity
For other peptide hormones (like growth
hormone) the receptor itself is not a kinase

Rather, it activates intracellular kinases
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Hydrophilic Hormones
Second-messenger systems
 Many hydrophilic hormones work through
second messenger systems
 Two have been described:


One involving cyclic adenosine
monophosphate (cAMP)
One that generates 2 lipid messengers:
inositol triphosphate (IP3) and diacyl
glycerol (DAG)
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Hydrophilic Hormones
Second-messenger systems
 Receptors are linked to a secondmessenger-generating enzyme via
membrane proteins called G proteins


Are thus called G-protein-coupled receptors
(GPCP)
When the G protein activates the enzyme, the
second-messenger molecules increase
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1. Receptors Function as Kinase Enzymes
2. Receptors Activate G Proteins
Hormones
Hormone
GPCR
Second messengergenerating enzyme
GPCR
Receptor
b g
GDP a
GTP
Inactive G
protein
Inactive
GTP
Active G
protein
Second
messenger
Active kinase
domain
ATP
Target
protein
ADP
Phosphorylated
protein
Cellular
response
Active
Protein
kinase
Inactive
protein kinase
Target
proteins
Cellular
response
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Paracrine Regulators
Paracrine regulation occurs in most organs
 Growth factors are proteins that promote
growth and cell division in specific organs




Epidermal growth factor = Skin
Nerve growth factor = Neurons
Insulin-like growth factor = Bone
Cytokines = Immune system
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Paracrine Regulators
Prostaglandins
 A diverse group of fatty acids that are
produced in almost every organ
 Regulate a variety of functions including:


Smooth muscle contraction, lung function,
labor, and inflammation
Synthesis is inhibited by nonsteroidal
anti-inflammatory drugs (NSAIDs)
such as aspirin and ibuprofen
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Paracrine Regulators
The endothelium of blood vessels is a rich
source of paracrine regulators
 Nitric oxide (NO) which promotes
vasodilation
 Endothelin which stimulates
vasoconstriction
 Bradykinin which promotes vasodilation
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The Pituitary Gland
The pituitary gland is also
known as the hypophysis
 It hangs by a stalk from the hypothalamus
The pituitary gland consists of two parts:
 Anterior pituitary (adenohypophysis)


Appears glandular
Posterior pituitary (neurohypophysis)

Appears fibrous
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Anterior Pituitary
Disorders
Growth hormone stimulates
growth of muscles and
connective tissue
 It also promotes the
production of insulin-like
growth factors

Stimulate cell division in the
epiphyseal growth plates, and
thus bone elongation
Gigantism is caused by an
excessive secretion of
growth hormone in a child
In contrast, pituitary
dwarfism is caused
by a deficiency in GH
secretion during
childhood
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Feedback mechanisms in
the control of blood
osmotic pressure—the
control of ADH.
The Thyroid Gland
In humans, the thyroid gland is shaped
like a bow tie, and lies just below the
Adam’s apple in the front of the neck
 It secretes:

Thyroid hormones
 Thyroxine
 Triiodothyronine
 Calcitonin
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The Thyroid Gland
Thyroid hormones bind to nuclear receptors
-Regulate carbohydrate & lipid metabolism
-Adults with hypothyroidism have
low production of thyroxine
-Reduced metabolism and overweight
-Adults with hyperthyroidism have
high production of thyroxine
-High metabolism and weight loss
-Trigger metamorphosis in amphibians
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The Parathyroid Glands
The parathyroid glands are
four small glands attached to
the thyroid
 Produce parathyroid
hormone (PTH) in
response to falling levels of
Ca2+ in blood


Stimulates osteoclasts to
dissolve calcium phosphate
crystals in the bone matrix and
release Ca2+ into blood
Stimulates the kidneys to
reabsorb Ca2+ from the urine
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The Adrenal Glands
The adrenal glands
are located just
above each kidney
 Medulla = Inner
portion


Stimulated by the
sympathetic division
of the autonomous
nervous system
Cortex = Outer
portion

stimulated
by the anterior
pituitary, through the hormone
ACTH
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The Pancreas
Insulin
-Secreted by beta (b) cells
of the islets
-Stimulates cellular uptake
of blood glucose and its
storage as glycogen in the
liver and muscle cells or as
fat in fat cells
Glucagon
-Secreted by alpha (a)
cells of the islets
-Promotes the hydrolysis
of glycogen in the liver
and fat in adipose tissue
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