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ENDOCRINE SYSTEM
Mechanisms of Chemical Signaling: a Review
Water-Soluble/Nonsteroid Hormones
Lipid-Soluble/Steroid Hormones
Control Pathways and Feedback Loops
• There are three types of hormonal control
pathways
Pathway
Example
Low blood
glucose
Stimulus
Receptor
protein
Pancreas
secretes
glucagon ( )
Endocrine
cell
Blood
Response
Example
Stimulus
Suckling
Sensory
neuron
Example
Pathway
Stimulus
Sensory
neuron
Hypothalamus/
posterior pituitary
Hypothalamus
Neurosecretory
cell
Posterior pituitary
secretes oxytocin
Blood
( )
vessel
vessel
Target
effectors
Pathway
Neurosecretory
cell
Blood
vessel
Hypothalamic
neurohormone
released in
response to
neural and
hormonal
signals
Hypothalamus
secretes prolactinreleasing
hormone ( )
Liver
Glycogen
breakdown,
glucose release
into blood
(a) Simple endocrine pathway
Target
effectors
Response
Smooth muscle
in breast
Milk release
Endocrine
cell
Blood
vessel
Anterior
pituitary
secretes
prolactin ( )
(b) Simple neurohormone pathway
Target
effectors
Response
Figure 45.2a–c
Mammary glands
Milk production
(c) Simple neuroendocrine pathway
One Chemical Signal, Different Effects
ENDOCRINE GLANDS
• Are ductless and secrete
hormones directly into the
bloodstream
• Target Cells – the cells that a
hormone directly affects;
if a cell does not have
receptors or the receptors
don’t respond, the hormone
has no effect.
Human
Endocrine
Glands
• Most hormones operate by a
negative feedback system or
feedback inhibition – a
stimulus produces a response
that opposes the original
stimulus; an environmental
change “feeds back” to inhibit
the original stimulus.
The Reproductive Cycle of the Human Female
THYROID GLAND
• Located in the neck, is the
target gland of thyroidstimulating hormone (TSH)
• When the thyroid is stimulated
by TSH it releases the
hormones Triiodothyronine (T3)
and Thyroxine (T4), which
regulates the metabolic rate of
your body tissues
Feedback control loops regulating the
secretion of thyroid hormones T3 and T4
PARATHYROID GLANDS
• These are four pea-shaped
organs that rest on the
thyroid. They secrete
parathyroid hormone which
increases blood calcium
levels – the opposite effect
of what calcitonin does
An example of how feedback regulation
maintains homeostasis
THE PITUITARY GLAND
• Often called the “master
gland” because it secretes
so many hormones (9 total!)
• Has two parts: Anterior
Pituitary and Posterior
Pituitary
Remember the acronym:
“MAP TO FLAG”
to remember the nine pituitary
hormones
• The pituitary sits just below
the hypothalamus which
regulates the anterior
pituitary by secreting
neurosecretory hormones
that can stimulate or inhibit
the actions of it
Hormones of the hypothalamus and pituitary
glands
Nerve cells that
release hormones
into the blood
ANTERIOR PITUITARY
• Secretes seven hormones:
–Growth Hormone (GH) –
stimulates bone and
muscle growth
–Adrenocorticotropic
Hormone (ACTH)
stimulates the adrenal
cortex to secrete
hormones (corticosteroids)
ADRENAL CORTEX
• ACTH – causes the
adrenal cortex to produce
its different hormones
•Glucocorticoids –
target the liver and
promote the release of
glucose
Adrenal Cortex:
• Mineralcorticoids – target the
kidney and promote the
retention of water
• Ex: Aldosterone – increases
recovery of Na and increases
excretion of K and H ions into
the urine
Anterior Pituitary Gland:
Thyroid-Stimulating Hormone (TSH)
• Stimulates the thyroid to secrete
thyroxine
Follicle-Stimulating Hormone (FSH)
• Stimulates the follicle to grow in
females, oogenesis, and
spermatogenesis
Anterior Pituitary Gland:
Luteinizing Hormone
• Causes the release of the
ovum during the menstrual
cycle in females and
testosterone production in
males
Anterior Pituitary Gland:
Prolactin
• Stimulates the mammary
glands to produce milk
Anterior Pituitary Gland
Melanocyte-Stimulating Hormone
(MSH) :
Regulates skin color in lower
vertebrates, although its function
in humans is unknown
Posterior Pituitary Gland:
• Secretes Two Hormones: (made by
hypothalamus)
• Antidiuretic Hormone (ADH) –
acts on the kidneys, increasing
water retention and thus
decreasing urine volume.
Posterior Pituitary Gland
•Oxytocin – is secreted by the
stimulation of the nipples
during breast feeding and
sexual intercourse; it also
stimulates uterine
contractions during labor
ADRENAL GLANDS
• Adrenal Medulla – secretes
epinephrine (adrenaline) and
norepinephrine(noradrenaline)
“fight-or-flight” response –
increase HR, BP, metabolism,
etc
Glucose homeostasis maintained by insulin
and glucagon
THE PANCREAS
• Glucagon – stimulates the
liver to convert glycogen
into glucose and to release
that glucose into the blood
• Insulin – has the opposite
effect of glucagon
Major Vertebrate Endocrine Glands and Some of
Their Hormones
Major Vertebrate Endocrine Glands and
Some of Their Hormones (Pancreas–Thymus)
What is the advantage of having
both a nervous system and an
endocrine system?
What does the hormone thyroxine
affect?
What is one effect of an iodine
deficient diet?
Insulin stimulates cell to remove
sugar from the blood while
___________ stimulates the release
of glucose from cells.
A shortage of dietary iodine makes
it impossible for the thyroid gland
to produce thyroxine. What would
happen to blood levels of thyroxine
and the thyroid gland as a result?
The role of ADH is to:
What is the difference between Type
I and Type II diabetes?
• The thyroid also increases
the concentration of
calcitonin which decreases
the blood’s concentration of
calcium.