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The Endocrine System
I. General Characteristics
• Endocrine glands
are ductless
• Exocrine glands
have ducts
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Endocrine Glands
Paracrine secretions
Endocrine glands
• act locally
• release hormones
• affect only neighboring cells
• hormones travel
through blood to target
cells
Autocrine secretions
• affect only the secreting cell
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Comparison of Nervous System
and Endocrine System
• Neurons release
neurotransmitters into
a synapse, affecting
postsynaptic cells
• Glands release
hormones into the
bloodstream
• Only target cells of
hormone responds
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Comparison of Nervous System
and Endocrine System
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Major
Endocrine
Glands
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II. Hormone Action

General Characteristics:





Needed in small amounts (potent)
Produces long-lasting effects
Regulate metabolic processes (homeostasis)
Regulated by negative feedback
Chemistry of Hormones

Steroid or Steroid-Like Hormones



sex hormones
adrenal cortex hormones
Nonsteroid Hormones (most hormones)




amines
proteins
peptides
glycoproteins
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Prostaglandins





paracrine substances
act locally
very potent in small amounts
regulate cellular responses to hormones
can activate or inhibit adenylate cyclase



controls cAMP production
alters cell’s response to hormones
wide variety of functions
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III. Control of Hormonal Secretions


Controlled by negative feedback mechanism
Control Sources: Hypothalamus, ANS, and by Regulating
Blood Levels
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Hormone Secretion is Under Negative
Feedback Control
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Pituitary Gland

Two portions



anterior pituitary
(adenohypophysis)
posterior pituitary
(neurohypophysis)
The pituitary gland is
attached to the
hypothalamus and lies in
the sella turcica of the
sphenoid bone.
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Pituitary Gland Control


Hypothalamic releasing hormones stimulate cells of anterior pituitary
to release hormones
Nerve impulses from hypothalamus stimulate nerve endings in the
posterior pituitary gland to release hormones
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Hypothalamic Hormones, Hormones from the
Anterior Pituitary and their Target Organs
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The overall scheme for the release of most hormones is in the above chart
(pg 501). First, the Hypothalamus secretes “releasing hormones” that target
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the anterior pituitary gland.
Posterior Pituitary Gland



Located behind anterior pituitary gland
Is continuous with nerve fibers of the
hypothalamus
Does not produce hormones (they are
produced by the hypothalamus), but stores
them until stimulated

Secretes 2 hormones:
Antidiuretic Hormone (video: Hormone
Communication)
 Oxytocin

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Thyroid Gland



Involved in
Iodine
uptake (to
produce T4
and T3). See
table 13.7
Thyroid
gland
consists of
two lobes
connected
bya an
isthmus
Follicular
cells secrete
thyroid
hormones
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Parathyroid Glands

4 small glands
embedded in the
posterior surface of
the thyroid gland
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Parathyroid Hormone
• PTH and calcitonin
to maintain
homeostasis of Ca+2
• PTH stimulates
bone to release Ca+2
and the kidneys to
conserve calcium. It
indirectly stimulates
the intestine to
absorb calcium. The
increase in blood
Ca+2 inhibits
secretion of PTH.
1.
2.a.
3.
2.b.
2.c.
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Parathyroid Hormone
Mechanism by which PTH promotes calcium absorption in
the intestine
• Vit. D is synthesized from
dietary cholesterol and
intestinal enzymes convert
it into provitamin D.
• Sun exposure changes it
into Vit. D (some also
comes from foods)
•The liver changes, stores
it, and with PTH, the
kidneys can control
absorbtion of Ca+2 ions
from the intestine.
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Adrenal Glands
• The adrenal glands
consist of an outer
cortex and inner
medulla.
•The cortex has 3
layers, or zones of
cells.
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Hormones of the Adrenal Cortex
• Aldosterone
increases blood
volume and
pressure by
promoting
conservation of
Na+1 and water
(steps 1-4).
Laser Disc
Slide 9 –
36490 Intro
to 39145
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Hormones of the Adrenal Cortex
• Negative
feedback
regulates
cortisol
secretion,
similar to the
regulation of
thyroid
hormone.
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Pancreas
• The hormone-secreting cells of the pancreas are grouped in clusters, or islets, that are
closely associated with blood vessels.
•Islets of Langerhans (pancreatic cells) secrete glucagon, insulin and somatostatin
(digestive enzymes).
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Insulin and Glucagon
• Insulin and glucagon together stabilize [blood glucose]
• Negative feedback responding to [blood glucose]
controls the levels of both hormones
• Glucagon
stimulates liver
(breaks down
glycagon to
glucose)
• Insulin forms
glycogen from
glucose
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Other Endocrine Glands
Pineal Gland
• secretes melatonin
• regulates circadian rhythms
Thymus Gland
• secretes thymosins
• promotes development of certain lymphocytes
• important in role of immunity
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Other Endocrine Glands
Reproductive
• ovaries produce estrogens and progesterone
• testes produce testosterone
• placenta produces estrogens, progesterone, and
gonadotropins
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Stress
Types of Stress
• physical stress
• psychological stress
Physical stress
• threatens tissues
• extreme hot/cold,
decreased [02], infections,
injuries, etc.
Psychological stress
• varies from person to
person
• thoughts from dangers,
grief, fear, anxiety, etc.
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Responses to Stress
•
•
•
•
•
•
•
•
•
•
•
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Life-Span Changes
• endocrine glands decrease in size
• muscular strength decreases as GH levels decrease
• ADH levels increase due to slower break down in liver
and kidneys
• calcitonin levels decrease; increase risk of
osteoporosis
• PTH level changes contribute to risk of osteoporosis
• insulin resistance may develop
• changes in melatonin secretion affect the body clock
• thymosin production declines increasing risk of
infections
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Negative Feedback Model
hormone 1
lowers
body condition
gland
high
specific body condition
low
raises
body condition
gland
hormone 2
2005-2006
Endocrine System Control
Feedback
Blood Sugar
insulin
body
cells take
up sugar
from blood
pancreas
high
liver stores
sugar
reduces
appetite
liver
blood sugar level
low
triggers
hunger
liver
releases
sugar
liver
pancreas
glucagon
2005-2006
Endocrine System Control
Blood Osmolarity
Feedback
ADH
increased
water
reabsorption
pituitary
increase
thirst
nephron
high
blood osmolarity
blood pressure
adrenal
gland
low
increased
water & salt
reabsorption
nephron
renin
aldosterone
angiotensin
angiotensinogen
2005-2006