the endocrine system ebaa m alzayadneh, dds, phd integrative physiology and pharmacology university...

The Endocrine System

Ebaa M Alzayadneh, DDS, PhD Integrative Physiology and Pharmacology

Un

ive

rsity

of

Jord

an

1

Overview of the endocrine system

Un

ive

rsity

of

Jord

an

2

Overview of the endocrine systemHormones are chemical messengers that are carried by the bloodstream to different cells in the body.

Hormones act at a distance from their place of production directly on the target cell, inciting it to increase or decrease the expression of specific genes.

Hormones can be either lipid-based, also known as steroidal, or protein-based, known as non-steroidal.

Lipid hormones enter the target cell directly through the cell membrane, and then travel to the nucleus and directly affect expression of target genes. Protein hormones cannot enter the cell, so they bind to receptors on the cell membrane, triggering a secondary messenger system within the cell.

University of Jordan

3

Overview of the endocrine systemHormone release by the endocrine system is regulated largely through negative feedback loops, and rarely through positive feedback loops. In negative feedback, increases in hormone activity lead to a decrease in the production of that hormone.

Endocrine glands in turn have no duct and release their secretions directly into the intercellular fluid or the blood.

The main endocrine glands are the pituitary (anterior and posterior lobes), thyroid, parathyroid, adrenal (cortex and medulla), pancreas and gonads.

University of Jordan

4

Nervous and Endocrine Systems:Act together to coordinate functions of all body systems

Nervous system Endocrine system

• Responds to stimuli by sending electrical action potentials along neurons using neurotransmitters, the chemical messenger of the nervous system.

• This response to stimuli is near instantaneous.

• The nervous system responds rapidly to short-term changes by sending electrical impulses.

• They may not last for long time (briefer)

• Specific target

• Hormones are synthesized at a distance from their target cells, and travel through the bloodstream or intercellular fluid

• This process takes significantly longer• effects are long lasting. Additionally,

target cells can respond to minute quantities of hormones and are sensitive to subtle changes in hormone concentration.

• Broad spectrum of targets

5

Endocrine Glands

• Glands are either:• Exocrine – have ducts• Endocrine – ductless

• Secrete hormones into interstitial fluid, diffuse into blood

• Endocrine glands:• Pituitary, thyroid, parathyroid, adrenal and pineal glands• Hypothalamus, thymus, pancreas, ovaries, testes, kidneys,

stomach, liver, small intestine, skin, heart, adipose tissue, and placenta not exclusively endocrine glands

Un

ive

rsity

of

Jord

an

6

Un

ive

rsity

of

Jord

an

7

Hormone Activity• Hormones affect only specific target tissues with specific

receptors• Receptors are constantly synthesized and broken down

Un

ive

rsity

of

Jord

an

8

Hormones types

• Circulating – circulate in blood throughout body

• Local hormones – act locally• Paracrine – act on

neighboring cells• Autocrine – act on the

same cell that secreted them

9

Chemical classes of hormones

• Lipid-soluble – use transport proteins• Steroid• Thyroid• Nitric oxide (NO)

• Water-soluble – circulate in “free” form• Amine• Peptide/ protein• Eicosanoid

Un

ive

rsity

of

Jord

an

10

Chemical classes of hormones

• Lipid-soluble – use transport proteins• Steroid• Thyroid• Nitric oxide (NO)

• Water-soluble – circulate in “free” form• Amine• Peptide/ protein• Eicosanoid

Un

ive

rsity

of

Jord

an

11

Chemical classes of hormones

•

12

Uni

vers

ity o

f Jor

dan

13

Uni

vers

ity o

f Jor

dan

Chemical classes of hormones

Mechanisms of Hormone Action• Response depends on both hormone and target cell• Lipid-soluble hormones bind to receptors inside target cells• Water-soluble hormones bind to receptors on the plasma membrane

• Activates second messenger system• Amplification of original small signal

• Responsiveness of target cell depends on• Hormone’s concentration• Abundance of target cell receptors• Influence exerted by other hormones:

• Permissiveness is the situation in which a hormone cannot exert its full effects without the presence of another hormone.

• Synergism occurs when two or more hormones produce the same effects in a target cell and their results are amplified.

• Antagonism occurs when a hormone opposes or reverses the effect of another hormone.

Un

ive

rsity

of

Jord

an

14

Un

ive

rsity

of

Jord

an

15

Water-solublehormone

Receptor

G protein

Blood capillary

Binding of hormone (first messenger)to its receptor activates G protein,which activates adenylate cyclase

Adenylate cyclase

Target cell

1

Water-solublehormone

Receptor

G protein

cAMP

Second messenger

Activated adenylatecyclase convertsATP to cAMP

Blood capillary

Binding of hormone (first messenger)to its receptor activates G protein,which activates adenylate cyclase

Adenylate cyclase

Target cell

ATP

1

2

Water-solublehormone

Receptor

cAMP serves as asecond messengerto activate proteinkinases

G protein

Protein kinases

cAMP

Second messenger

Activated adenylatecyclase convertsATP to cAMP

Blood capillary

Binding of hormone (first messenger)to its receptor activates G protein,which activates adenylate cyclase

Adenylate cyclase

Target cell

ATP

1

2

3 Activatedproteinkinases

Water-solublehormone

Receptor

cAMP serves as asecond messengerto activate proteinkinases

G protein

Protein kinases

cAMP

Activatedproteinkinases

Second messenger

Activated adenylatecyclase convertsATP to cAMP

Activated proteinkinasesphosphorylatecellular proteins

Blood capillary

Binding of hormone (first messenger)to its receptor activates G protein,which activates adenylate cyclase

Adenylate cyclase

Target cell

ATP

1

2

4

3

Protein— P

ADP

Protein

ATP

Water-solublehormone

Receptor

cAMP serves as asecond messengerto activate proteinkinases

G protein

Protein kinases

cAMP

Activatedproteinkinases

Protein—

Second messenger

Activated adenylatecyclase convertsATP to cAMP

Activated proteinkinasesphosphorylatecellular proteins

Millions of phosphorylatedproteins cause reactions thatproduce physiological responses

Blood capillary

Binding of hormone (first messenger)to its receptor activates G protein,which activates adenylate cyclase

Adenylate cyclase

Target cell

P

ADP

Protein

ATP

ATP

1

2

4

3

5

Water-solublehormone

Receptor

cAMP serves as asecond messengerto activate proteinkinases

G protein

Protein kinases

cAMP

Activatedproteinkinases

Protein—

Second messenger

Phosphodiesteraseinactivates cAMP

Activated adenylatecyclase convertsATP to cAMP

Activated proteinkinasesphosphorylatecellular proteins

Millions of phosphorylatedproteins cause reactions thatproduce physiological responses

Blood capillary

Binding of hormone (first messenger)to its receptor activates G protein,which activates adenylate cyclase

Adenylate cyclase

Target cell

P

ADP

Protein

ATP

ATP

1

2

6

4

3

5

Water-soluble Hormones

Un

ive

rsity

of

Jord

an

16

1 Lipid-solublehormonediffuses into cell

Blood capillary

Target cell

Transportprotein

Free hormone

1 Lipid-solublehormonediffuses into cell

Blood capillary

Activatedreceptor-hormonecomplex altersgene expression

NucleusReceptor

mRNA

DNACytosol

Target cell

Transportprotein

Free hormone

2

1 Lipid-solublehormonediffuses into cell

Blood capillary

Activatedreceptor-hormonecomplex altersgene expression

NucleusReceptor

mRNANewly formedmRNA directssynthesis ofspecific proteinson ribosomes

DNACytosol

Target cell

Transportprotein

Free hormone

Ribosome

2

3

1 Lipid-solublehormonediffuses into cell

Blood capillary

Activatedreceptor-hormonecomplex altersgene expression

NucleusReceptor

mRNANewly formedmRNA directssynthesis ofspecific proteinson ribosomes

DNACytosol

Target cell

New proteins altercell's activity

Transportprotein

Free hormone

Ribosome

Newprotein

2

3

4

Lipid-soluble Hormones

Control of Hormone Secretion• Regulated by

• Signals from nervous system

• Chemical changes in the blood

• Other hormones• Most hormonal

regulation by negative feedback• Few examples of

positive feedback

Un

ive

rsity

of

Jord

an

17