Transcript Endocrine System - T.R. Robinson High School

Endocrine System
Hormones
2007-2008
Overview of the Endocrine System
• All of an animal’s hormonesecreting cells collectively
are its endocrine system
• Hormone-secreting glands
(the endocrine glands) are
ductless glands because
they secrete their chemical
messengers directly into
extracellular fluid which
then move to the
bloodstream.
Overview of the Endocrine System
• Many endocrine
glands occur in
pairs, like the
adrenal glands
• Some are
singular glands,
like the
pancreas
What are hormones?
• Hormones are chemical messengers that
are released in one part of the body but
affect another part of the body
• Hormones are transported thru the blood
• The cells that are affected by a hormone
are called its target cells
• A target cell responds to a hormone
because it has specific receptors for that
hormone.
Hormone receptors are found either exposed
on the surface of the cell or within the cell,
depending on the type of hormone. Binding of
a hormone to its receptor triggers a cascade
of reactions within the cell that affects
function.
Regulation
• Why are hormones needed?
– chemical messages from one body
part to another
– communication needed to
coordinate whole body
– daily homeostasis & regulation of
large scale changes
• solute levels in blood
– glucose, Ca++, salts, etc.
•
•
•
•
•
metabolism
growth
development
maturation
reproduction
growth hormones
Animals rely on 2 systems for regulation
endocrine system
• system of ductless glands
–
–
–
–
secrete chemical signals directly into blood
chemical travels to target tissue
target cells have receptor proteins
slow, long-lasting response
nervous system
• system of neurons
– transmits “electrical” signal &
release neurotransmitters to
target tissue
– fast, short-lasting response
Regulation by chemical messengers
• Neurotransmitters released by neurons
• Hormones release by endocrine glands
endocrine gland
neurotransmitter
axon
hormone
carried by blood
receptor proteins
receptor proteins
target cell
Lock & Key
system
Classes of hormones
Hormone
Type
Example
Steroid
(Lipidbased)
Estrogen 
One effect of example
hormone
Increases thickness of uterine
lining
Also: testosterone
Peptide
Insulin 
Promotes glucose uptake by
(Proteinbody cells
based) Also: FSH, LH, ADH
Tyrosine
derivative
Thyroxin 
Increases metabolic rate
How hormones act on target cells
• (Lipid-based) Steroid hormones
– hydrophobic & lipid-soluble
• diffuse across cell membrane & enter cells
• bind to receptor proteins in cytoplasm & nucleus
• bind to DNA as transcription factors = turn on genes
• (Protein-based) Peptide hormones
– hydrophilic & not lipid soluble
•
•
•
•
can’t diffuse across cell membrane
bind to receptor proteins in cell membrane
trigger secondary messenger pathway
activate internal cellular response
– enzyme action, uptake or secretion of molecules…
Action of Steroid hormones
steroid hormone
target cell
S
S
cytoplasm
1
blood
S
protein
carrier
cross cell membrane
2
binds to receptor protein
becomes
transcription factor
5
S
3
mRNA read by ribosome
plasma membrane
4
DNA
mRNA
nucleus
6
protein
7
protein secreted
ex: secreted protein = growth factor (hair, bone, muscle, gametes)
Action of Peptide hormones
signal-transduction pathway
1
protein
hormone
P
signal
plasma membrane
binds to receptor protein
activates
G-protein
activates enzyme
cAMP
receptor
protein
activates
cytoplasmic
signal
GTP
cytoplasm
target cell
acts as 2° messenger
transduction
ATP
ATP
activates
enzyme
2
secondary
messenger
system
activates
enzyme
produces an action
3
response
Animation of Steroid hormones
http://www.rattlerscience.com/life/classes/apbiolo
gy/documents/Unit%204/45_Lectures_PPT/media/
45_03bLipidSolubleHormone_A.swf
Animation of Peptide hormones
http://www.rattlerscience.com/life/classes/apbiology/docum
ents/Unit%204/45_Lectures_PPT/media/45_03aWaterSolu
bleHormone_A.swf
Benefits of a 2° messenger system
signal
1
Activated adenylyl cyclase
receptor protein
2
Not yet
activated
amplification
4
3
GTP
amplification
cAMP
amplification
5
G protein
protein kinase
6
amplification
Amplification!
enzyme
Cascade multiplier!
FAST response!
7
amplification
product
Maintaining homeostasis
hormone 1
lowers
body condition
gland
high
specific body condition
low
raises
body condition
gland
hormone 2
Negative Feedback
Model
Nervous System Control
Feedback
Controlling Body Temperature
nerve signals
hypothalamus
dilates surface
blood vessels
sweat
high
body temperature
(37°C)
low
hypothalamus
constricts surface shiver
blood vessels
nerve signals
Endocrine System Control
Feedback
Regulation of Blood
Sugar
islets of Langerhans
insulin
beta islet cells
liver stores
glycogen
body
cells take
up sugar
from blood
pancreas
liver
high
blood sugar level
(90mg/100ml)
low
triggers
hunger
liver
releases
glucose
liver
pancreas
glucagon
islets of Langerhans
alpha islet cells
reduces
appetite
Endocrine System Control
Feedback
Blood Osmolarity
osmoreceptors in
hypothalamus
ADH
increased
water
reabsorption
pituitary
increase
thirst
nephron
high
blood osmolarity
blood pressure
nephron
adrenal
gland
low
increased
water & salt
reabsorption
JuxtaGlomerular
Apparatus
nephron
(JGA)
renin
aldosterone
angiotensinogen
angiotensin
Nervous & Endocrine systems linked
• Hypothalamus = “master nerve control center”
(part of the nervous system)
– receives information from nerves around body
about internal conditions
– releasing hormones: regulates release of
hormones from pituitary
• Pituitary gland = “master gland”
(part of the endocrine system)
hypothalamus
– secretes broad range
of “tropic” hormones
posterior
regulating other
pituitary
glands in body
anterior
tropic hormones = target endocrine glands
hypothalamus
thyroid-stimulating
hormone
(TSH)
Thyroid gland
Adrenal
cortex
posterior antidiuretic
pituitary hormone
(ADH)
anterior
pituitary
gonadotropic
hormones:
folliclestimulating
hormone (FSH)
& luteinizing
hormone (LH)
Kidney
tubules
Muscles
of uterus
Melanocyte
in amphibian
Bone
and muscle
Testes
Ovaries
Mammary
glands
in mammals
Hypothalamus & posterior lobe of pituitary
• Specialized nerve cells
called neurosecretory
cells connect the two
• The dendrites and cell
bodies are located in the
hypothalamus and the
axons extend down into
the posterior pituitary
• Certain hormones like
ADH and oxytocin are
produced in the cell bodies
but move down the axon
into the posterior pituitary.
Hypothalamus and anterior lobe of pituitary
• Works differently: The hypothalamus has
capillary beds which take in hormones produced
from the hypothalamus itself (called ‘releasing
hormones’, for ex. gonadotrophin-releasing
hormone, GnRH)
• The capillaries join the portal vein which
extends down into the anterior pituitary
• The hormones leave the bloodstream for their
target cells in the anterior pituitary
• These hormones cause the cells to secrete other
specific hormones
• Ex. GnRH causes secretion of FSH and LH,
which are secreted and sent to the gonads of
both females and males
Hypothalamus and anterior lobe of pituitary
Example of different effects from one hormone
What does this tell you about these hormones?
How could these hormones have different effects?
same gene family
gene duplication?
prolactin
mammals
milk
production
birds
fat
metabolism
fish
amphibians
salt &
water
balance
metamorphosis
& maturation
growth
hormone
growth
& development
ADH secretion and negative feedback
• Good example of negative feedback relationship
between hypothalamus and pituitary gland
• ADH (Vasopressin) = hormone which controls
how much water is reabsorbed from the
collecting duct in kidney nephrons back into
blood
– If ADH is secreted, the collecting duct
becomes permeable to water, so more water
leaves the collecting duct by osmosis
– If ADH is not secreted, the collecting duct is
impermeable to water and so urine contains a
relatively high water content
• ADH is produced by dendrites of the
neurosecretory cells that extend from
hypothalamus to posterior pituitary
• It is transported down and stored in
membrane-bound granules in nerve endings in
the posterior pituitary
• Osmoreceptor cells in the hypothalamus
monitor the blood plasma concentration
– Too concentrated? Impulses are sent to posterior
pituitary to secrete ADH (thus water is reabsorbed
back in to the bloodstream)
– Too dilute? No impulse is sent, therefore no ADH
is secreted (so water remains in urine)