Transcript Endocrine System

Cells communicate with each other
through direct contact with other cells or
from a distance via chemical signaling
ENDOCRINE SIGNALS ARE PRODUCED BY
ENDOCRINE CELLS THAT RELEASE
SIGNALING MOLECULES, WHICH ARE
SPECIFIC AND CAN TRAVEL LONG DISTANCES
THROUGH THE BLOOD TO REACH ALL PARTS
OF THE BODY
Endocrine Communication
 Animal hormones
are chemical signals
that are secreted into
the circulatory system
and communicate
regulatory messages
within the body
 Hormones reach all
parts of the body, but
only target cells are
equipped to respond
Two systems coordinate communication throughout the
body: the endocrine system and the nervous system
 The endocrine
system secretes
hormones that
coordinate slower but
longer-acting
responses including
reproduction,
development, energy
metabolism, growth,
and behavior
 The nervous system
conveys high-speed
electrical signals along
specialized cells called
neurons; these signals
regulate other cells
Endocrine
signals
(hormones)
are secreted
into
extracellular
fluids and
travel via the
bloodstream
Endocrine Signaling
Local regulators are
chemical signals that
travel over short
distances by diffusion
Local regulators help
regulate blood pressure,
nervous system
function, and
reproduction
Two types


Paracrine signals
act on cells near
the secreting cell
Autocrine signals
act on the
secreting cell itself
Paracrine and Autocrine
Signaling
At synapses, neurons
often secrete chemical
signals called
neurotransmitters
that diffuse a short
distance to bind to
receptors on the target
cell
Neurohormones are a
class of hormones that
originate from neurons
in the brain (i.e.
hypothalamus) and
diffuse through the
bloodstream to act on
target cells (possibly an
endocrine gland to
produce a 2nd hormone).
Synaptic Signaling and
Neuroendocrine Signaling
Signaling by
any of these
hormones
involves
three key
events:



Reception
Signal
transduction
Response
Receptor Location Varies with
Hormone
The same hormone
may have different
effects on target cells
that have
Different
receptors for the
hormone
 Different signal
transduction
pathways
 Different
proteins for
carrying out the
response
A hormone can also
have different effects
in different species

One Hormone – Different Effects
Fig. 45-10
Major endocrine glands:
Hypothalamus
Pineal gland
Pituitary gland
Thyroid gland
Parathyroid glands
Organs containing
endocrine cells:
Thymus
Heart
Adrenal
glands
Testes
Liver
Stomach
Pancreas
Kidney
Kidney
Small
intestine
Ovaries
A negative
feedback loop
inhibits a
response by
reducing the
initial stimulus
Negative
feedback
regulates many
hormonal
pathways
involved in
homeostasis
Insulin &
Glucagon: control
blood glucose
Pancreas contains clusters
of endocrine cells known
as Islets of Langerhans
Islets of Langerhans
contain alpha and beta
cells
Beta cells secrete insulin
which triggers uptake of
glucose from the blood
Alpha cells secrete
glucagon which promotes
the release of glucose into
the blood
Hormones secreted into
the interstitial fluid and
enter circulatory system
Insulin &
Glucagon
Insulin – stimulates
nearly all body cells to
take up glucose;
Insulin – slows glycogen
breakdown in liver and
glucose production
Glucagon –targets cells in
liver to increase glycogen
hydrolysis – release
glucose into the
bloodstream
Negative Feedback –
stimulus leads to release
of hormone which works
on target cell to bring
about response; response
shuts off hormone
Causes:
1.Deficiency of insulin
2.Decreased response to
insulin
Results in increased
blood glucose levels
Body forced to use fat as
main fuel – can result in
acidic metabolite build
up lowering pH
Kidney can’t handle high
level of glucose in blood
= sugar in urine leading
to frequent urination
and extreme thirst
Diabetes Melitus
Insulin-dependent
diabetes is an
autoimmune disorder in
which the immune
system destroys the beta
cells of the pancreas
Often thought of as
childhood diabetes
Destroys a person’s
ability to produce insulin
Treatment = insulin
injections
Type I Diabetes
Target cells fail to
respond to insulin –
blood glucose levels
remain high
Develops with age –
usually around 40
Excess weight and lack
of exercise can
contribute to type 2
diabetes
Most common form of
diabetes
Type 2 Diabetes
Human Growth
Hormone
Releasing hormones from
hypothalamus trigger
anterior pituitary to
secrete growth hormone
Growth Hormone has
Tropic effects (regulates
other endocrine cells) and
Nontropic effects (targets
nonendocrine cells)
Major target of GH is the
liver which secretes IGF’s
(insulin-like growth
factors) which stimulate
bone and cartilage growth
Gigantism
Hypersecretion of
GH during
childhood can lead
to gigantism
Person grows
unusually tall
Results in
overgrowth of
extremities in
adults
(acromegaly)
Dwarfism
Hyposecretion of
GH in childhood
retards long-bon
growth and can
pituitary dwarfism
If diagnosed before
puberty, can be
treated with HGH
Thyroid
Hormones
The thyroid gland
consists of two lobes on
the ventral surface of
the trachea
It produces two iodinecontaining hormones:
triiodothyronine
(T3) and thyroxine
(T4)
The thyroid is
regulate by Thyroid
Stimulating
Hormone (TSH)
from the antior
pituitary
Thyroid Gland
Triiodothyroxine (T3)
called T3 because it has
three iodine atoms
thyroxine (T4) called T4
because it has four
iodine atoms
Both have basically the
same effect:
1.
Bone and nerve cell
development
2.
Help maintain
normal blood
pressure, heart rate,
muscle tone,
digestion &
reproductive
function
Hyperthyroidism
Hyperthyroidism,
excessive secretion of
thyroid hormones,
causes high body
temperature, weight
loss, irritability, and high
blood pressure
Graves’ disease is a form
of hyperthyroidism in
humans
In Grave’s disease, the
body's natural defense
(immune) system attacks
the thyroid gland. The
thyroid fights back by
making too much
thyroid hormone
Hypothyroidism
Hypothyroidism, low
secretion of thyroid
hormones, causes
weight gain, lethargy,
and intolerance to cold
Iodine
Deficiency
Severe iodine
deficiency causes
problems because
the thyroid can never
produce enough T3
and T4 but is still
continually
stimulated by TSH
resulting in
elargement
childhood can cause
cretinism
Adulthood can cause
goiter
Goiter – Excess TSH enlarge
the thyroid gland results in a
large swelling just above the
breast bone. Rarely, it may
constrict the trachea
(windpipe) or esophagus and
cause difficulty breathing or
swallowing. The rest of the
symptoms come from thyroxin
or the lack of it.
Cretinism – congenital
condition due to thyroid
hormone deficiency
during fetal development
and marked in childhood
by dwarfed structure,
mental retardation
dystrophy of the bones,
and low basal
metabolism
Antidiuretic
Hormone
Neurosecretory cells
extend from the
hypothalamus into the
posterior pituitary
where ADH is released
into the blood stream
Antidiuretic
hormone (ADH)
enhances water
reabsorption in the
kidneys
Luteinizing Hormone and Follicle Stimulating Hormone
Male
Females
Estrogen
 Estrogens, most
importantly
estradiol, are
responsible for
maintenance of the
female reproductive
system and the
development of female
secondary sex
characteristics
Testosterone
 The testes primarily
synthesize androgens,
mainly testosterone,
which stimulate
development and
maintenance of the male
reproductive system
 Testosterone causes an
increase in muscle and
bone mass and is often
taken as a supplement to
cause muscle growth,
which carries health risks
Fig. 45-16
Pathway
Example
Stimulus
Suckling
+
Sensory
neuron
Positive feedback
Hypothalamus/
posterior pituitary
Neurosecretory
cell
Blood
vessel
Target
cells
Response
Posterior pituitary
secretes oxytocin ( )
Smooth muscle in
breasts
Milk release
Positive Feedback Hormones
 Oxytocin induces
uterine contractions
and the release of milk
 Suckling sends a
message to the
hypothalamus via the
nervous system to
release oxytocin,
which further
stimulates the milk
glands