ENDOCRINE SYSTEM
Chapter 16
Endocrine vs Nervous System
NERVOUS
• Uses action potentials along
axons & chemical
neurotransmitters at synapses
• Receptors are on post-
ENDOCRINE
• Uses chemical hormones
released from glands into the
blood
• Receptors are on the plasma
synaptic membrane
membranes of target cells or
intercellular
• Signals are very fast
• Signals are slower (seconds
(milliseconds)
to days)
• Response is immediate but
• Response is delayed but
short-lived
more sustained
HORMONES
• Hormones – chemical substances secreted
by cells into blood stream
– Regulate metabolic function of other cells
– Are either peptides or steroids
Hormone - Target Cell Specificity
• circulate to all tissues but affect
activity of only certain cells, these are
their target cells
• specificity of effect governed by
hormone receptors
Characteristics of Hormones
• Hormones:
– exert effects some distance from where
produced
– active at very low (pg to ng) concentrations in
the blood
– have short half-life in body - secs to mins
Characteristics of Hormones
• their effect is to alter cell activity. The
precise response depends on the target cell
type. Typical cellular effects include:
– Altering plasma membrane permeability
– Stimulating protein synthesis
– Activating enzymes
– Inducing secretory activity
– Stimulating mitosis
Control of Hormone Release
• Synthesis & release of most hormones
are regulated by negative feedback.
– As hormone levels rise, they cause target
organ effects that inhibit hormone
release.
Chemical Classes of Hormones
• Amines - Derived from tyrosine or tryptophan.
Includes: epinephrine, T4, & melatonin.
• Proteins & peptides - Made from amino acid
chains. Includes: antidiuretic hormone,
growth hormone, & insulin.
• Glycoproteins - A polypeptide chain bound to
one or more carbohydrates. Includes: folliclestimulating hormone & luteinizing
hormone.
• Steroids - Lipids derived from cholesterol.
Includes: testosterone, estradiol, &
cortisol.
Mechanisms of Hormone Action
• Hormones:
– Diffuse through the cell membrane &
bind to intracellular receptors (steroid
hormones & T4) or bind to receptors on
the membrane of distant cells (aminoacid based hormones).
– Carry out their effects by direct gene
activation (steroids) or through signal
transduction systems (amino-acid based).
Distribution of Endocrine
Tissue
• Specialized organs (pituitary,
adrenal, thyroid)
• Discrete clusters within other
organs (pancreas, gonads)
• Cells dispersed singly within
other tissues (enteroendocrine
cells)
GLAND
HORMONE
NORMAL EFFECTS
OF HORMONE
REGULATION
OF RELEASE
TARGET
ORGAN
EFFECTS OF
HYPER- &
HYPOSECRETION
Neurohypophysis
(posterior pituitary)
Adenohypophysis
(anterior pituitary)
GROWTH HORMONE
• Gigantism - a
hypersecretion of growth
hormone during infancy,
childhood or adolescence,
while epiphyseal growth
plates remain open.
12 year-old with mother
GROWTH HORMONE
• Acromegaly - GH
hypersecretion in
adulthood, when
epiphyseal plates are
closed.
Large, spade-like hands
of acromegaly
GROWTH HORMONE
• Dwarfism - GH
deficiency in childhood,
leading to a maximum
height of 4 feet with
normal body proportions.
Dwarfed brothers with
researcher in India
THYROID HORMONE
• Cretinism - results from
severe hypothyroidism in
children. The children are
mentally retarded, with a
short body & a thick neck
& tongue.
THYROID HORMONE
• Myxedema - Due to
hypothyroidism in adults.
Symptoms of low
metabolic rate, chills,
lethargy, mental
sluggishness, & swelling
of body tissues.
Swelling associated
with myxedema
THYROID HORMONE
• If myxedema results from
a lack of iodine, the
thyroid enlarges &
protrudes into a condition
called goiter.
THYROID HORMONE
Exophthalmos typical
of Grave’s
• Grave’s Disease - The
most common
hyperthyroid pathology is
characterized by elevated
metabolic rate (rapid
heartbeat, sweating,
nervousness) &
exophthalmos (protrusion
of the eyeballs).
ANTIDIURETIC HORMONE
• Diabetes insipidus
is a result of ADH
deficiency, a
syndrome marked
by intense thirst &
very high urine
output
Routes of
Aldosterone
Stimulation
GLUCOCORTICOIDS
• At high concentrations, cortisol has
pronounced anti-inflammatory & antiimmune effects including:
– Depressing cartilage & bone formation
– Inhibiting inflammation by stabilizing
lysosomal membranes
GLUCOCORTICOIDS
• Cushing’s disease results from glucocorticoid
excess. Symptoms include
persistent hyperglycemia,
a moon face, & a
redistribution of fat to the
abdomen & posterior neck
(causing a “buffalo
hump”).
GLUCOCORTICOIDS
• Addison’s disease - the major
hyposecretory disorder of the
adrenal cortex, usually
involving both glucocorticoids
& mineralcorticoids. Patients
have low blood sugar &
JFK had Addison’s, which he sodium, & Caucasians show an
kept from public knowledge
increase in skin pigmentation
(bronzing)
GONADOCORTICOIDS
• Androgenital syndrome is
due to hypersecretion of
androgens. Most often
apparent in women, it
manifests itself in hirsutism
(including beard
development).
Olga Roderick, the
“Bearded Lady”
Pancreatic Hormones
INSULIN
• After glucose enters a target cell,
insulin binding triggers enzymatic
activity that:
– Catalyze the oxidation of glucose for
ATP production
– Join glucose molecules together to form
glycogen
– Convert excess glucose to fat
INSULIN
• Diabetes mellitus - Due to
hyposecretion (Type I) or
hypoactivity (Type II) of insulin.
When insulin is absent or
deficient, blood sugar levels
remain high after a meal because
glucose is unable to enter most
tissue cells.
DIABETES
• Type I (insulin-dependent) - afflicts 1.5
million Americans.
– Autoimmune disease (beta cells are attacked
by immune cells).
– Insulin is not produced or secreted, requiring
regular injections.
DIABETES
• Type II (non-insulin-dependent) afflicts 19 million Americans.
– Insulin resistance - Insulin is usually
produced but the receptors do not respond.
– Heredity & lifestyle both play roles in the
disease.
DIABETES
• Three clinical signs of diabetes:
– Hyperglycemia -normal blood sugar
should be 80 - 120 mg/dl.
– Glucosuria - glucose spills into the urine
at high blood concentrations (300 mg/dl).
– Ketoacidosis & ketouria - as sugar is not
available for fuel & lipolysis accelerates.
DIABETES
• Three cardinal signs of diabetes (the three
polys):
Polyuria - excessive urination; glucosuria
leads to osmotic diuresis & dehydration
Polydipsia - excessive thirst, caused by
dehydration
Polyphagia - ravenous hunger & food
consumption, a sign the person is “starving
in the land of plenty”
PINEAL GLAND
• Still somewhat of a mystery, the pineal gland
(or body) within the brain secretes melatonin.
MELATONIN
• Melatonin - made from the neurotransmitter
serotonin, a derivative of the amino acid
tryptophan.
– Levels peak at night & fall in the daytime
– Changing melatonin levels may influence
physiological processes that show rhythmic
variation: sleep, body temperature, & appetite
MELATONIN
The Midnight
Sun
• Seasonal affective disorder
(SAD) has been linked to
elevated melatonin levels in
the winter months for people
in northern latitudes like
Alaska. It may lead to
depression, long bouts of
sleeping, & eating binges.