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

Fee

db

ack

inh

ibit

ion

Fee

db

ack

inh

ibit

ion Sensor cell

Effectorcell

Fee

db

ack

inh

ibit

ion

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

Locomotion

Respiration

Excretion

Nutrition

Swim via movements of muscular tail

Gas exchange occurs in gills, across skin,and in lungs

Most are herbivorous; have a long gutspecialized for digesting algae and plants

Most nitrogenous wastes excreted asammonia

Adult frog

Locomotion

Respiration

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?