April 28, 2014 – Chemical signals and hormones II
Announcements:
Lab this week will meet in the computer labs
Final Exam: May 15
ICES evaluation
1. Pre-lecture quiz
2. Review of cell-to-cell signaling & thyroid hormones (T3 & T4)
3. Specificity
1. Lipid soluble hormones – Steroids
2. G-coupled protein receptors –
3. Tyrosine kinase receptors
4. Hormone-mediated physiological tradeoffs
Endocrine systems are regulated by negative feedback
Endocrine pathway
Neuroendocrine pathway
Stimulus
Neuroendocrine-to-endocrine pathway
Stimulus
Stimulus
Endocrine cell
Endocrine
signal
Effector
cell
Response
Sensor cell
Sensor cell
Neural signal
Neural signal
CNS
CNS
Neuroendocrine
signal
Effector
cell
Response
Neuroendocrine
signal
Endocrine cell
Endocrine
signal
Effector
cell
Response
Chemical characteristics of hormones – major classes
Peptides and Polypeptides
Secretin
Amino Acid
Derivatives
Steroids
Cortisol
Epinephrine
Receptor
Receptor
Not lipid soluble;
bind to receptors on
surface of target cell
Target cell
Most not lipid soluble;
bind to receptors on
surface of target cell
Lipid soluble;
bind to receptors
inside target cell
Receptor
Hormone Transport and Action on Target
Hydrophobic messengers pass into
cell where they bind with
transcription factors which affect
gene expression.
Hydrophilic hormones bind to a
receptor on the cell membrane
which causes several reactions
known as a signal transduction
pathway. This can affect the
properties of enzymes/proteins, etc.
or it may affect gene expression.
Thyroid Hormone
Thyroid hormone:
- Actually two hormones (T3/T4)
Mammals mainly secrete T4
- but some T4 is converted under certain
circumstances
- Same receptor binds both,
but ↑affinity for T3
T3/T4 are membrane soluble
- ↑metabolism in muscles, heart, liver & kidney
T4
T3
Figure 47-8
T3
T3
Juvenile frog (tadpole)
Adult frog
Locomotion
Swim via movements of muscular tail
Locomotion
Tailless; walk or hop
Respiration
Gas exchange occurs in gills, across skin,
and in lungs
Respiration
Gas exchange occurs across skin, and in
lungs
Nutrition
Most are herbivorous; have a long gut
specialized for digesting algae and plants
Nutrition
Excretion
Most nitrogenous wastes excreted as
ammonia
Most are carnivorous; have a large mouth
or long tongue for catching prey; short gut
specialized for digesting proteins
Excretion
Most nitrogenous wastes excreted as urea
Thyroid hormone levels go up as flat fish go through this
metamorphosis.
Anadromous versus Resident Stream Sticklebacks
Higher metabolic rates
Lower metabolic rates
Migrate from ocean to freshwater
to breed
Permanent residents in
freshwater
Bigger
Smaller
Take home message: The same hormone can
have multiple physiological effects
How do we explain this?
Altering individual behaviors by altering overall thyroid
levels seems like a pretty blunt way to go about changing
specific phenotypes.
How could this system be fine-tuned to optimize specific
traits under different contexts?
A.) changes in TRH expression
B.) changes in TSH expression
C.) alterations of TSH receptors
D.) alteration of T3/T4 receptors in specific cell types.
Hormonal specificity: G-protein coupled receptors
Hormonal specificity: G-protein coupled receptors
Hormonal specificity: Tyrosine kinase receptors
Hormonal specificity: Steroids and gene transcription
STEROID HORMONE ACTION
Nucleus
Hormone
receptor
Steroid
hormone
mRNA
Proteins
DNA
Hormonereceptor
complex
1. Steroid
2. Hormone binds
hormone
enters
target cell.
to receptor, induces
conformational
change.
Hormoneresponse
element
RNA
polymerase
3. Hormone-receptor
4. Many mRNA
complex enters
nucleus and binds
to DNA, induces
start of transcription.
transcripts are
produced,
amplifying
the signal.
Ribosome
5. Each transcript is
translated many times,
further amplifying the
signal.
Hormone-mediated Tradeoffs:
Interactions between stress, reproduction and immune function
Extraordinary ordinary Junco: http://juncoproject.org/videos/chapter-2/
Hormone-mediated Tradeoffs
Interactions between stress, reproduction and immune function
Stress
Short-Term Stress Response
“Fight or flight” response is stimulated by epinephrine
Figure 47-7a-hypothesis
Figure 47-7b-setup
Some additional effects of the “fight or flight response
1.) Redirection of blood flow from the skin and digestive system
toward heart, brain, and muscles.
2.) Relaxation vascular smooth muscle to aid in vasodilation
Take home message:
1.) Short term stress responses are EXTREMELY beneficial over
the short term.
2.) Prolonged stress responses can be harmful.
*Radio Lab episode on stress: http://www.radiolab.org/story/91580-stress/
Long term stress responses
Feedback inhibition by cortisol on ACTH
Hypothalamus
Pituitary gland
Adrenal
gland
Results of injecting ACTH into human volunteers
This graph shows the . . .
a. Positive influence ACTH has on cortisol release
b. Inhibitory feedback of cortisol on ACTH release
Results of injecting cortisol into human volunteers
This graph shows the . . .
a. Positive influence ACTH has on cortisol release
b. Inhibitory feedback of cortisol on ACTH release
ure 47-15
Stressed
individual
Unstressed
individual
ACTH also stimulates the release of aldosterone. Why should this
be a part of the stress response?