Transcript Endocrine System - Dr. Annette M. Parrott

Endocrine System
Dr. Annette M. Parrott
GPC
BIOL1612
Endo crine System
“inside”
“secrete”
• Odd organ system
– Compared to nervous sys. &
digestive sys.
• Endocrine glands usually not
connected
– Considered a “system” because of
functional similarity
• Secrete chemical messages
called hormones to target cells
“to excite”
Also skin, heart, GI tract, placenta, kidneys, adipose tissue
Principal functions of the endocrine
system
• Maintenance of the
internal environment in
the body (maintaining the
optimum biochemical
environment).
• Integration and
regulation of growth and
development.
• Control, maintenance and
instigation of sexual
reproduction and
development.
Glands with a sensing and signaling
system which regulates the
duration and magnitude of hormone
release via feedback from the
target cell.
Types of hormones
• Hormones are categorized into four
structural groups, with members of
each group having many properties in
common:
– Peptides and proteins (polypeptides)
– Amino acid derivatives
– Steroids (cholesterol based)
– Fatty acid derivatives - Eicosanoids (mostly
paracrines, i.e. leukotrines, prostaglandins)
Types of hormones
• Peptides
– “Chains” of amino acids
• 4 – 200+ amino acids
– Water soluble
– Largest # of hormones
•
•
•
•
•
Hypothalamus
Pituitary (Ant. & Post.)
Islets of Langerhans
Parathyroid hormone
Digestive system
hormones
Peptide/protein hormone synthesis
Types of hormones
• Amino Acid Based
– Tyrosine derivatives
• Thyroid hormones
– Thyroxine (T4)
– Triiodothyronine (T3)
• Catecholamines/Adrenal medulla
– Epinephrine
– Norepinephrine
» Both neurohormones &
neurotransmitter
– Tryptophan derivatives
(precursor to serotonin and the
pineal hormone melatonin)
– Glutamic acid (converted to
histamine)
• Steroids
Types of hormones
– Derivatives of cholesterol
differing in side chains
– Four covalently-bonded
rings
– Lipid soluble (freely
diffuse, not stored, not
packaged)
• Adrenal cortex
• Gonads
• Examples
– Glucocorticoids (cortisol major
representative in mammals)
– Mineralocorticoids (aldosterone
most prominent)
– Androgens (i.e. testosterone)
– Estrogens (i.e. estradiol and
estrone)
– Progestogens (i.e. progestins)
Types of hormones
• Fatty Acid
Derivatives Eicosanoids
– Eicosanoids are a large
group of molecules
derived from
polyunsaturated fatty
acids.
– The principal groups of
hormones of this class
are prostaglandins,
prostacyclins,
leukotrienes and
thromboxanes.
How does hormone type affect it’s activation of
target cells?
Mechanisms of Hormone Action
• Lipid-soluble steroids
& thyroid hormones
– Diffuse through
plasma membrane
– Enter nucleus
– Forms “hormonereceptor complex”
– H-R complex binds as
transcription factors
to chromosome to
activate/inactivate
gene(s)
Mechanisms of Hormone Action
• Peptides & watersoluble amines
– Hormone (A) binds to
receptor on cell surface
– Activates G- protein
– Activates adenylate
cyclase
• Converts ATP to cAMP
– cAMP activates protein
kinases, which produce
final effect.
Signal Transduction Pathway Animation
Transduction Pathway Epinephrine
Mechanisms of Hormone Action
• Peptides & watersoluble amines
– Other Hormone (B) binds to
receptor on cell surface
– Activates G- protein
– Inhibits adenylate cyclase
• Stops ATP to cAMP
–  inhibits final effect of
first hormone
Which cells are activated by hormones?
Hormone Targets
•A cell is a target because is has a specific receptor for the
hormone
•Most hormones circulate in blood, coming into contact with
essentially all cells. However, a given hormone usually affects
only a limited number of cells, which are called target cells.
•A target cell responds to a hormone because it bears
receptors for the hormone.
Which diagram represents…
Steroid hormones?
Lipid hormones?
Peptide hormones?
Target cell
concept
Receptor
Target cell
Hormone
Target cell
concept
Not all hormones
find their target
How are chemical signals
sent to cells?
Types of cell-to-cell signaling
•Classic endocrine hormones
travel via bloodstream to target
cells
•Neurohormones are released via
synapses and travel via the
bloostream
•Paracrine hormones act on
adjacent cells
•Autocrine hormones are
released and act on the cell that
secreted them
•Intracrine hormones act within
the cell that produces them
Response vs. distance traveled
Endocrine action: the hormone is distributed in blood and
binds to distant target cells.
Paracrine action: the hormone acts locally by diffusing
from its source to target cells in the neighborhood.
Autocrine action: the hormone acts on the same cell that
produced it.
Ways of influencing target cells
Within
beside/near
self
close to
Create a Venn diagram comparing the nervous & endocrine systems
Endocrine vs. Nervous System
• Major communication
systems in the body
• Integrate stimuli and
responses to changes in
external and internal
environment
• Both are crucial to
coordinated functions of
highly differentiated
cells, tissues and organs
• Unlike the nervous
system, the endocrine
system is anatomically
discontinuous.
Nervous Sys. vs Endocrine Sys.
• The nervous system exerts point-topoint control through nerves, similar
to sending messages by conventional
telephone. Nervous control is
electrical in nature and fast.
• The endocrine system broadcasts
its hormonal messages to essentially
all cells by secretion into blood and
extracellular fluid. Like a radio
broadcast, it requires a receiver to
get the message - in the case of
endocrine messages, cells must bear
a receptor for the hormone being
broadcast in order to respond.
Regulation of hormone
secretion
• Sensing and signaling: a biological need is
sensed, the endocrine system sends out a
signal to a target cell whose action addresses
the biological need. Key features of this
stimulus response system are:
·
·
·
·
·
receipt of stimulus
synthesis and secretion of hormone
delivery of hormone to target cell
evoking target cell response
degradation of hormone
Receipt of Stimulus
• Humoral in response
to changing blood levels
• i.e. PTH regulation of Ca2+ via
parathyroid
• Neural in response to
nerve fibers
• i.e.
catecholamines
(norepinephrine & epinephrine)
from adrenal medulla
• Hormonal in response
to other hormones
• i.e.
GHRH
secreted
by
hypothalamus which regulates GH
secretion by anterior pituitary
Inputs to endocrine cells
Control of Endocrine Activity
The concentration of hormone as seen by target
cells is determined by three factors:
•Rate of production
•Rate of delivery
• Permissiveness/Synergism/Antagonism
• Upregulation (insipidus)/downregulation (Type II,
melitus)
•Rate of degradation and elimination
What is a feedback loop?
Feedback Control of Hormone
Production
•Feedback loops are
used extensively to
regulate secretion of
hormones
•Negative feedback
occurs when a change in
a physiological variable
triggers a response that
counteracts the initial
fluctuation
Negative Feedback
• Neurons in the hypothalamus
secrete thyroid releasing hormone
(TRH), which stimulates cells in the
anterior pituitary to secrete
thyroid-stimulating hormone (TSH)
• TSH binds to receptors on
epithelial cells in the thyroid gland,
stimulating synthesis and secretion
of thyroid hormones, which affect
probably all cells in the body
• When blood concentrations of
thyroid hormones increase above a
certain threshold, TRH-secreting
neurons in the hypothalamus are
inhibited and stop secreting TRH.
Feedback control
• Negative feedback is most common: for
example, LH from pituitary stimulates the
testis to produce testosterone which in turn
feeds back and inhibits LH secretion
• Positive feedback is less common: examples
include LH stimulation of estrogen which
stimulates LH surge at ovulation
Positive & Negative Feedback
Diseases of the Endocrine System
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Cushing's Syndrome
Acromegaly
Pheochromocytoma
Glucagonoma
Somatostatinoma
Diabetes mellitus
Diabetes insipidus
Hyperthyroidism (Graves disease)
Hypothyroidism (Goiter)
Hypothyroidism (Cretinism in babies)
Hypothyroidism (Myxedema)
Achondroplasia (Dwarfism)
Gigantism
SADS (Seasonal Affective Disorder):
Disorders of the Endocrine System
Acromegaly
Simple Goiter
Disorders of the Endocrine System
Cushing’s Disease
Achondroplasia