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Anatomy & Physiology
Endocrine System
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Pg. 131
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General Characteristics of
Endocrine System
• The endocrine system assists the nervous system with
communication and control of the body
• The cells, tissues, and organs are called endocrine glands
• They are ductless
• They use the bloodstream
• They secrete hormones
• There are also similar glands called paracrine and
autocrine glands that are quasi-endocrine
• Other glands that secrete substances are the exocrine glands
• They have ducts
• They deliver their products directly to a specific site
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Nerve impulse
Neuron
transmits
nerve
impulse
Glandular
cells secrete
hormone into
bloodstream
Neurotransmitter
released into
synapse
Bloodstream
Postsynaptic
cell responds
Target cells
(cells with hormone
receptors) respond
to hormone
Hormones have no
effect on other cells
(b)
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Hormone Action
•Hormone – a very powerful
substance (chemical messenger)
secreted by a endocrine gland into
the bloodstream, that affects the
function of another cell or “target
cell”
-needed in very small amounts
(very potent)
-produce long-lasting effects in the
target cells
-regulate metabolic processes
(homeostatic)
-regulated by negative feedback
mechanisms
Hypothalamus
Pituitary gland
Parathyroid gland
Pineal gland
Thyroid gland
Thymus
Adrenal gland
Kidney
Pancreas
Ovary
(in female)
Testis
(in male)
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Chemistry of Hormones
Chemically, hormones are either:
• Steroid or steroid-like hormones such as:
• Sex hormones
• Adrenal cortex hormones
• Non-steroid hormones such as:
• Amines
• Proteins
• Peptides
• Glycoproteins
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Control of Hormonal Secretions
• Primarily controlled by negative feedback mechanism
• Hormones can be short-lived or may last for days
• Hormone secretions are precisely regulated
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Control Sources
Control center
Endocrine gland
inhibited.
Receptors
Hormone control
mechanism senses
change.
Stimulus
Hormone levels rise or
controlled process
increases.
Effectors
Hormone secretion
decreased.
Response
Hormone levels
return toward
normal.
too high
Normal
hormone
levels
too low
Stimulus
Hormone levels drop or
controlled process
decreases.
Receptors
Hormone control
mechanism senses
change.
Response
Hormone levels
return toward
normal.
Effectors
Hormone secretion
increased.
Control center
Endocrine gland
stimulated.
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Control Sources
–
–
Hypothalamus
–
Nervous system
Changing level
of substance
in plasma
– Anterior pituitary gland
(a)
Peripheral
endocrine
gland
Endocrine
gland
Endocrine
gland
Target cells
Target cells
Target cells
Action
Action
Action
(b)
(c)
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Hypothalamus
• During hormonal control, endocrine organs are stimulated
by hormones from other endocrine organs, starting with
the hypothalamus
• Directs activities of the pituitary gland by secreting
hypothalamic releasing hormones and hypothalamic
nonreleasing hormones to stimulate or inhibit release of
hormones from the pituitary gland
• Very small gland buried deep in the brain below the
thalamus
• Plays an important role in regulating everyday functions
such as metabolism, heart rate, energy level, body
temperature, thirst, nutrient intake, blood pressure, and
blood composition.
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Hypothalamus
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Pituitary Gland
• Lies at the base of the brain in the sella turcica, small depression
in the sphenoid bone of the skull
• Known as the “master gland” because of its major influence on
body’s activities (but still controlled by the hypothalamus)
• Size of a grape
• Connected to hypothalamus by a stalk called infundibulum
• Consists of two distinct portions:
• Anterior pituitary (adenohypophysis) – hormonally
controlled
• Posterior pituitary (neurohypophysis)- neurally controlled
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Anterior Pituitary Hormones
• Hypothalamic releasing hormones stimulate cells of anterior
pituitary to release hormones
•Produces 6 hormones:
• Growth hormone (GH)-growth and development; helps fat be
used for energy, saving glucose to maintain blood sugar levels
Third ventricle
• Prolactin hormone (PR)-aka LTH, develops breast tissue and
stimulates production of milk after childbirth
• Thyroid-stimulating hormone (TSH)-stimulates growth and
secretion of thyroid
• Adrenocorticotropic hormone (ACTH)-stimulates growth and
secretion of adrenal cortex
• Follicle-stimulating hormone (FSH)-production of estrogen in
females; production of sperm in males
• Luteinizing hormone (LH)-production of estrogen and
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progesterone
in
females;
production
of
testosterone
in
males
Anterior lobe of pituitary gland
Posterior lobe of pituitary gland
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Hormones from Hypothalamus
GHRH
SS
Growth
Somatostatin
hormonereleasing
hormone
PRF
Prolactinreleasing
factor
PIH
Prolactinrelease
inhibiting
hormone
TRH
Thyrotropinreleasing
hormone
CRH
Corticotropinreleasing
hormone
GnRH
Gonadotropinreleasing
hormone
Hormones from Anterior Pituitary
GH
Growth
hormone
Bone
Muscle Adipose
tissue
PRL
Prolactin
Mammary gland
TSH
Thyroidstimulating
hormone
Thyroid
ACTH
Adrenocorticotropic
hormone
Adrenal
cortex
LH
Luteinizing
hormone
Ovary
FSH
Folliclestimulating
hormone
Testis
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Posterior Pituitary Hormones
• Structurally consists of nerve fibers and neuroglia v.
glandular epithelial cells of the anterior pituitary gland
• The nerve fibers originate in the hypothalamus
•Nerve impulses from hypothalamus stimulate nerve endings
in the posterior pituitary gland to release hormones
• Two hormones are stored here:
• Antidiuretic hormone (vasopressin): maintains water balance
by increasing absorption of water in kidney tubules
• Oxytocin: released during childbirth causing strong
contractions when a mother breastfeeds; synthetic form known
as Pitocin
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