April 28, 2014 – Chemical signals and hormones II
Announcements:Lab this week will meet in the computer labsFinal Exam: May 15 ICES evaluation
1. Pre-lecture quiz2. Review of cell-to-cell signaling & thyroid hormones (T3 & T4)3. Specificity
1. Lipid soluble hormones – Steroids2. G-coupled protein receptors – 3. Tyrosine kinase receptors
4. Hormone-mediated physiological tradeoffs
Neuroendocrine pathway
Neuroendocrinesignal
Endocrine pathway Neuroendocrine-to-endocrine pathway
Neuroendocrinesignal
Endocrinesignal
Endocrinesignal
Endocrine cell
Effectorcell
Response
Response
Stimulus Stimulus
Feed
back
inhi
bitio
n
Feed
back
inhi
bitio
n Sensor cell
Effectorcell
Feed
back
inhi
bitio
n
Neural signal
CNS
Stimulus
Sensor cell
Neural signal
CNS
Response
Effectorcell
Endocrine cell
Endocrine systems are regulated by negative feedback
Steroids
CortisolEpinephrine
Amino AcidDerivatives
Receptor
Secretin
Peptides and Polypeptides
Receptor
Receptor
Target cell
Most not lipid soluble;bind to receptors onsurface of target cell
Not lipid soluble;bind to receptors onsurface of target cell
Lipid soluble;bind to receptorsinside target cell
Chemical characteristics of hormones – major classes
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 transductionpathway. 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
Juvenile frog (tadpole)
T3
LocomotionRespiration
Excretion
Nutrition
Swim via movements of muscular tailGas exchange occurs in gills, across skin,and in lungsMost are herbivorous; have a long gutspecialized for digesting algae and plantsMost nitrogenous wastes excreted asammonia
Adult frog
LocomotionRespiration
Nutrition
Excretion
Gas exchange occurs across skin, and inlungs
Tailless; walk or hop
Most nitrogenous wastes excreted as urea
Most are carnivorous; have a large mouthor long tongue for catching prey; short gutspecialized for digesting proteins
Thyroid hormone levels go up as flat fish go through this metamorphosis.
Anadromous versus Resident Stream Sticklebacks
Higher metabolic rates
Migrate from ocean to freshwater to breed
Bigger
Lower metabolic rates
Permanent residents in freshwater
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 expressionB.) changes in TSH expressionC.) alterations of TSH receptorsD.) 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
STEROID HORMONE ACTIONHormonereceptor
Steroidhormone
Hormone-receptorcomplex
Hormone-responseelement
RNApolymerase
DNA
mRNA
Nucleus
Proteins
Ribosome3. Hormone-receptorcomplex entersnucleus and bindsto DNA, inducesstart of transcription.
1. Steroidhormoneenterstarget cell.
2. Hormone bindsto receptor, inducesconformationalchange.
4. Many mRNAtranscripts areproduced,amplifyingthe signal.
5. Each transcript istranslated many times,further amplifying thesignal.
Hormonal specificity: Steroids and gene transcription
Hormone-mediated Tradeoffs:Interactions between stress, reproduction and immune function
Extraordinary ordinary Junco: http://juncoproject.org/videos/chapter-2/
Hormone-mediated TradeoffsInteractions 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
This graph shows the . . . a. Positive influence ACTH has on cortisol releaseb. Inhibitory feedback of cortisol on ACTH release
This graph shows the . . . a. Positive influence ACTH has on cortisol releaseb. Inhibitory feedback of cortisol on ACTH release
ACTH also stimulates the release of aldosterone. Why should this be a part of the stress response?
