what is the function (purpose) of this system? (clue: one

Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings

Endocrine System: Overview

What is the function (purpose) of this system?

(clue: one word)


Communication!

The role of hormones is to provide communication between cells (tissues and organs).

There are other chemical substances that communicate effects on the same cells that secrete them but these are called AUTOCRINES. And chemical substances that act locally effecting other cells nearby called PARACRINES. For example, EICOSANOIDS are lipids with local hormone–like activity.

Autocrines, paracrines (such as eicosanoids) are not considered hormones since hormones are long-distance chemical signals.



How does it function (communicate) differently than the nervous system?

(clues: spatial and time)


Target Cell Specificity

Nerve cells communicate directly with one or several other nerve cells whereas:

� Hormones circulate to all tissues but only activate cells referred to as target cells

� Target cells must have specific receptors to which the hormone binds

� These receptors may be intracellular or located on the plasma membrane



� Have lag times ranging from seconds to hours

� Tend to have prolonged effects



Communicate what messages?

What is it telling other cells to do?


Mechanism of Hormone Action

Endocrine system – the body’s second great

controlling system which influences metabolic activities of cells by means of hormones

Hormones produce one or more of the following cellular changes in target cells

� Alter plasma membrane permeability

� Stimulate protein synthesis

� Activate or deactivate enzyme systems

� Induce secretory activity

� Stimulate mitosis



What organs comprise the endocrine system?

What tissues and organs in the body produce hormones


Major Endocrine Organs

Figure 16.1

Islets of Langerhans in the



� Endocrine glands – pituitary, thyroid, parathyroid,

adrenal, pineal, and thymus

� The pancreas and gonads produce both hormones

and exocrine products

� The hypothalamus has both neural functions and

releases hormones

� Other tissues and organs that produce hormones –

adipose cells, pockets of cells in the walls of the small intestine, stomach, kidneys, and heart


Types of Hormones

What are hormones made of?

Which of the organic molecules that we studied - carbohydrates, lipids, protein or nucleic acids?


Types of Hormones

� A few slides earlier I mentioned EICOSANOIDS

which are lipids. Two types of eicosanoids are leukotrienes and prostaglandins.

� When we studied proteins we talked about hormones (and neurotransmitters and enzymes) being made of

protein. Amino acid based hormones are Amines, thyroxine, peptide, and many other protein hormones.

� When we studied lipids I mentioned STEROLS such as steroids which are also hormones. gonadal and adrenocortical are steroids (hormones).



We know how the nervous system sends its messages, by depolarization, action potentials, neurotransmitters and then receptors.

How does a hormone work…that is, how does it send its message?


Hormone Action

Hormone connects to receptor located on the cell

surface or inside the cell. Remember “lock and key”.


Hormone Action

But what happens after that?


Hormone Action

What happens next depends on on the type of hormone and target cell.

In some cases, the hormone has a direct effect

on DNA activating a gene. STEROID

hormones work this way.

In other cases involving AMINO ACID based

(protein) hormones, there is a second

messenger involved and regulatory G

proteins.


Hormone Action

Let’s take a look at the STEROID hormones which have a direct effect on DNA activating a gene.


Steroid Hormones

When a steroid goes directly to the DNA (gene) what do you imagine it would do there? What would it cause to happen?

You may have forgotten but last semester we studied nucleic acids and DNA is used for only one thing…what is that?


Steroid Hormones

� DNA is used only to make one molecule of the other three we studied.

� Carbohydrate, lipid, and protein

� Which one is it? And why does DNA code for only one? How are the others made?


Steroid Hormones

Steroids interact with the DNA causing it to produce mRNA (the process called transcription).

Then what happens?

� The mRNA is translated into proteins, which bring about a cellular effect


Steroid Hormones

Steroids interact with the DNA causing it to produce mRNA (the process called transcription).

Then what happens?

� The mRNA is translated into proteins, which bring about a cellular effect. Some of the proteins may be enzymes that will make the other molecules (lipid and carbohydrates and nucleic acids).


Steroid Hormones

Lets take a look at what this might look like using graphic images in sequence.


Steroid

hormoneCytoplasm

Figure 16.4


Steroid

hormone

Steroid

hormone

Cytoplasm

Figure 16.4

nucleus

nuclear pores


Steroid

hormone

Steroid

hormone

Cytoplasm

Receptor-chaperonincomplex

Figure 16.4


Steroid

hormone

Steroid

hormone

Cytoplasm


Molecularchaperones

Receptor-hormonecomplex

Figure 16.4


Steroid

hormone

Steroid

hormone

Cytoplasm


Molecularchaperones


Hormone

responseelements

Binding

Chromatin

Figure 16.4


Hormoneresponseelements

Binding

Transcription

Chromatin

mRNA

Nucleus

Figure 16.4



Binding

Transcription

Chromatin

mRNA

Nucleus

Ribosome

mRNA

Figure 16.4



Binding

Transcription

Chromatin

mRNA

Nucleus

New proteinTranslation

Ribosome

mRNA

Figure 16.4


Steroidhormone

Steroidhormone

Cytoplasm

Receptor-chaperonin

complex

Molecular

chaperones



Binding

Transcription

Chromatin

mRNA

Nucleus

New proteinTranslation

Ribosome

mRNA

Figure 16.4


Hormone Action

Now let’s talk about the protein hormones and how they deliver their message.


Amino Acid-Based Hormone Action: cAMP Second Messenger

� Hormone (first messenger) binds to its receptor, which then binds to a G protein

� The G protein is then activated as it binds GTP, displacing GDP

� Activated G protein activates the effector enzyme adenylate cyclase

� Adenylate cyclase generates cAMP (second messenger) from ATP

� cAMP activates protein kinases, which then cause cellular effects


Receptor

Hormone A

ReceptorGTP GTP

GTP GTP GTP GTP

ATPcAMP

Inactive

protein kinase A

Active

protein kinase A

Catecholamines

ACTHFSHLH

GlucagonPTH

TSHCalcitonin

Triggers responses of targetcell (activates enzymes,stimulates cellular

secretion, opens ionchannels, etc.)

Adenylate cyclase Hormone B

GDPGDP

Extracellular fluid

Cytoplasm

Gs Gi

1

2 34

3 2

1

5

Figure 16.2

Amino Acid-Based Hormone Action: cAMPSecond Messenger


Hormone A

Receptor

Catecholamines

ACTHFSHLH

GlucagonPTH

TSHCalcitonin

Adenylate cyclase

Extracellular fluid

Cytoplasm

Gs

Figure 16.2



Hormone A

Receptor

Catecholamines

ACTHFSHLH

GlucagonPTH

TSHCalcitonin

Adenylate cyclase

Extracellular fluid

Cytoplasm

Gs

1

Figure 16.2



Hormone A

ReceptorGTP

GTP

Catecholamines

ACTHFSHLH

GlucagonPTH

TSHCalcitonin

Adenylate cyclase

GDP

Extracellular fluid

Cytoplasm

Gs

1

2

Figure 16.2



Hormone A

ReceptorGTP

GTP GTP

Catecholamines

ACTHFSHLH

GlucagonPTH

TSHCalcitonin

Adenylate cyclase

GDP

Extracellular fluid

Cytoplasm

Gs

1

2 3

Figure 16.2



Hormone A

ReceptorGTP

GTP GTP

ATPcAMP

Catecholamines

ACTHFSHLH

GlucagonPTH

TSHCalcitonin

Adenylate cyclase

GDP

Extracellular fluid

Cytoplasm

Gs

1

2 34

Figure 16.2



Hormone A

ReceptorGTP

GTP GTP

ATPcAMP

Inactive

protein kinase A

Active

protein kinase A

Catecholamines

ACTHFSHLH

GlucagonPTH

TSHCalcitonin



Adenylate cyclase

GDP

Extracellular fluid

Cytoplasm

Gs

1

2 34

5

Figure 16.2



Receptor

Catecholamines

ACTHFSHLH

GlucagonPTH

TSHCalcitonin


Extracellular fluid

Cytoplasm

Gi

Figure 16.2



Receptor

Catecholamines

ACTHFSHLH

GlucagonPTH

TSHCalcitonin


Extracellular fluid

Cytoplasm

Gi

1

Figure 16.2



ReceptorGTP

GTP

Catecholamines

ACTHFSHLH

GlucagonPTH

TSHCalcitonin


GDP

Extracellular fluid

Cytoplasm

Gi

2

1

Figure 16.2



ReceptorGTP

GTP GTP

Catecholamines

ACTHFSHLH

GlucagonPTH

TSHCalcitonin


GDP

Extracellular fluid

Cytoplasm

Gi

3 2

1

Figure 16.2



Receptor

Hormone A

ReceptorGTP GTP

GTP GTP GTP GTP

ATPcAMP

Inactive

protein kinase A

Active

protein kinase A

Catecholamines

ACTHFSHLH

GlucagonPTH

TSHCalcitonin




GDPGDP

Extracellular fluid

Cytoplasm

Gs Gi

1

2 34

3 2

1

5

Figure 16.2



GTP PIP2

IP3

ReceptorGTP

GTP

Catecholamines

TRHADH

GnRHOxytocin

Triggers responses

of target cell

GDP

Extracellular fluid

Cytoplasm

Inactiveprotein

kinase C

Activeprotein kinase C

Phospholipase C

Gq

Ca2+ Ca2+- calmodulin

Hormone

Endoplasmic

reticulum

DAG1

2 34 5

5

6

Figure 16.3

Amino Acid-Based Hormone Action: PIP Mechanism


Receptor

Catecholamines

TRHADH

GnRHOxytocin

Extracellular fluid

Cytoplasm

Gq

Hormone

Figure 16.3



Receptor

Catecholamines

TRHADH

GnRHOxytocin

Extracellular fluid

Cytoplasm

Gq

Hormone

1

Figure 16.3



GTP

ReceptorGTP

Catecholamines

TRHADH

GnRHOxytocin

GDP

Extracellular fluid

Cytoplasm

Gq

Hormone

1

2

Figure 16.3



GTP PIP2

ReceptorGTP

GTP

Catecholamines

TRHADH

GnRHOxytocin

GDP

Extracellular fluid

Cytoplasm

Phospholipase C

Gq

Hormone

1

2 3

Figure 16.3



GTP PIP2

IP3

ReceptorGTP

GTP

Catecholamines

TRHADH

GnRHOxytocin

GDP

Extracellular fluid

Cytoplasm

Phospholipase C

Gq

Hormone

DAG1

2 34

Figure 16.3



GTP PIP2

IP3

ReceptorGTP

GTP

Catecholamines

TRHADH

GnRHOxytocin

GDP

Extracellular fluid

Cytoplasm

Inactiveprotein

kinase C


Phospholipase C

Gq

Ca2+

Hormone

Endoplasmic

reticulum

DAG1

2 34 5

5

Figure 16.3



GTP PIP2

IP3

ReceptorGTP

GTP

Catecholamines

TRHADH

GnRHOxytocin

Triggers responses

of target cell

GDP

Extracellular fluid

Cytoplasm

Inactiveprotein

kinase C


Phospholipase C

Gq

Ca2+ Ca2+- calmodulin

Hormone

Endoplasmic

reticulum

DAG1

2 34 5

5

6

Figure 16.3



Amino Acid-Based Hormone Action: cAMP Second Messenger

I would like you just to know that the following molecules underlined are involved.

Hormone (first messenger) binds to its receptor, which then binds to a G protein

� The G protein is then activated as it binds GTP, displacing GDP

� Activated G protein activates the effector enzyme adenylatecyclase

� Adenylate cyclase generates cAMP (second messenger) from ATP

� cAMP activates protein kinases, which then cause cellular effects


What do you think might cause a hormone to work more or less?


What do you think might cause a hormone to work more or less?

� Blood levels of the hormone

� Relative number of receptors on the target cell

� The affinity of those receptors for the hormone


The number of receptors on the target cells can change!

� Up-regulation – target cells form more receptors in response to the hormone

� Down-regulation – target cells lose receptors in response to the hormone


Remember!

Hormones circulate in the blood. Since some hormones are lipid, they do not mix with blood (water) so they must be combined (bound) with a (plasma) protein.

This means that steroids and thyroid hormone are attached to plasma proteins (or are said to be bound).

All other protein hormones mix well in blood plasma (water) and are not bound (not encumbered).


What happens to hormones after they do their job?


What happens to hormones after they do their job?

Hormones are removed from the blood by:

� Degrading enzymes

� The kidneys

� Liver enzyme systems


Hormones act alone and together.

� Permissiveness – one hormone cannot exert

its effects without another hormone being

present

� Synergism – more than one hormone

produces the same effects on a target cell

� Antagonism – one or more hormones opposes

the action of another hormone


What causes hormones to be synthesized (made) and released?



� Tropic substances

� Humoral stimuli

� Neural stimuli

� Hormonal stimuli

Let’s briefly discuss each one and consider one example of each.



� Tropic substances

The pineal gland releases tropic substances that effect the hypothalamus and pituitary gland. Pineal gland release is under influence of diurnal and seasonal cycles.


Humoral Stimuli

� Humoral stimuli – secretion of hormones in direct response to changing blood levels of ions and nutrients

� Example: concentration of calcium ions in the blood

� Declining blood Ca2+ concentration stimulates the parathyroid glands to secrete PTH (parathyroid hormone)

� PTH causes Ca2+ concentrations to rise and the stimulus is removed


Humoral Stimuli

Figure 16.5a


Neural Stimuli

� Neural stimuli – nerve fibers stimulate hormone release

� Preganglionic

sympathetic nervous

system (SNS) fibers

stimulate the adrenal

medulla to secrete

catecholamines

Figure 16.5b


Hormonal Stimuli

� Hormonal stimuli – release of hormones in response to hormones produced by other endocrine organs

� The hypothalamic hormones stimulate the

anterior pituitary

� In turn, pituitary hormones stimulate targets to

secrete still more hormones


Hormonal Stimuli

Figure 16.5c


Endocrine Organs – LAB EXERCISE

Figure 16.1

Islets of Langerhans in the

And Other Hormone-Producing Structures

� Kidneys – secrete erythropoietin, which signals the production of red blood cells

� Skin – produces cholecalciferol, the precursor of vitamin D

� Adipose tissue – releases leptin, which is involved in the sensation of satiety, and stimulates increased energy expenditure

Identify these

organs and

learn the names and

primary functions of

the hormones

they secrete.

what is the function (purpose) of this system? (clue: one

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