the endocrine system ebaa m alzayadneh, dds, phd integrative physiology and pharmacology university...
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The Endocrine System
Ebaa M Alzayadneh, DDS, PhD Integrative Physiology and Pharmacology
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Overview of the endocrine system
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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.
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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.
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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
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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
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Hormone Activity• Hormones affect only specific target tissues with specific
receptors• Receptors are constantly synthesized and broken down
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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
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Chemical classes of hormones
• Lipid-soluble – use transport proteins• Steroid• Thyroid• Nitric oxide (NO)
• Water-soluble – circulate in “free” form• Amine• Peptide/ protein• Eicosanoid
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Chemical classes of hormones
• Lipid-soluble – use transport proteins• Steroid• Thyroid• Nitric oxide (NO)
• Water-soluble – circulate in “free” form• Amine• Peptide/ protein• Eicosanoid
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Chemical classes of hormones
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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.
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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
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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
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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
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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
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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
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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
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Water-soluble Hormones
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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
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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
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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
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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
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