The Endocrine System: Part A
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Transcript of The Endocrine System: Part A
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PowerPoint® Lecture Slides prepared by Janice Meeking, Mount Royal College
C H A P T E R
Copyright © 2010 Pearson Education, Inc.
16The Endocrine System: Part A
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Endocrine System: Overview
• Acts with the nervous system to coordinate and integrate the activity of body cells
• Influences metabolic activities by means of hormones transported in the blood
• Responses occur more slowly but tend to last longer than those of the nervous system
• Endocrine glands: pituitary, thyroid, parathyroid, adrenal, and pineal glands
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Copyright © 2010 Pearson Education, Inc. Figure 16.1
Pineal glandHypothalamusPituitary gland
Parathyroid glands(on dorsal aspectof thyroid gland)Thymus
Thyroid gland
Adrenal glands
Pancreas
Ovary (female)
Testis (male)
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Chemical Messengers
• Hormones: long-distance chemical signals that travel in the blood or lymph
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Chemistry of Hormones
• Two main classes
1.Amino acid-based hormones
• Amines, thyroxine, peptides, and proteins
2.Steroids
• Synthesized from cholesterol
• Gonadal and adrenocortical hormones
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Mechanisms of Hormone Action
• Hormone action on target cells1. Alter plasma membrane permeability of
membrane potential by opening or closing ion channels
2. Stimulate synthesis of proteins or regulatory molecules
3. Activate or deactivate enzyme systems4. Induce secretory activity5. Stimulate mitosis
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Mechanisms of Hormone Action
• Two mechanisms, depending on their chemical nature
1. Water-soluble hormones (all amino acid–based hormones except thyroid hormone)
• Cannot enter the target cells
• Act on plasma membrane receptors
• Coupled by G proteins to intracellular second messengers that mediate the target cell’s response
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Mechanisms of Hormone Action
2. Lipid-soluble hormones (steroid and thyroid hormones)
• Act on intracellular receptors that directly activate genes
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Plasma Membrane Receptors and Second-Messenger Systems • cAMP signaling mechanism
1.Hormone (first messenger) binds to receptor
2.Receptor activates G protein
3.G protein activates adenylate cyclase
4.Adenylate cyclase converts ATP to cAMP (second messenger)
5. cAMP activates protein kinases
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Plasma Membrane Receptors and Second-Messenger Systems • cAMP signaling mechanism• Activated kinases phosphorylate various
proteins, activating some and inactivating others
• cAMP is rapidly degraded by the enzyme phosphodiesterase
• Intracellular enzymatic cascades have a huge amplification effect
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Copyright © 2010 Pearson Education, Inc. Figure 16.2
Hormone (1st messenger)binds receptor.
Receptoractivates Gprotein (GS).
G proteinactivatesadenylatecyclase.
cAMP acti-vates proteinkinases.
Adenylatecyclaseconverts ATPto cAMP (2ndmessenger).
Receptor
G protein (GS)
Adenylate cyclase
Triggers responses oftarget cell (activatesenzymes, stimulatescellular secretion,opens ion channel,etc.)
Hormones thatact via cAMPmechanisms:
EpinephrineACTHFSHLH
Inactiveprotein kinase
Extracellular fluid
Cytoplasm
Activeproteinkinase
GDP
GlucagonPTHTSHCalcitonin
1
2 3 4
5
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Copyright © 2010 Pearson Education, Inc. Figure 16.2, step 1
Hormone (1st messenger)binds receptor.
Receptor
Hormones thatact via cAMPmechanisms:
EpinephrineACTHFSHLH
Extracellular fluid
Cytoplasm
GlucagonPTHTSHCalcitonin
1
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Copyright © 2010 Pearson Education, Inc. Figure 16.2, step 2
Hormone (1st messenger)binds receptor.
Receptoractivates Gprotein (GS).
Receptor
G protein (GS)
Hormones thatact via cAMPmechanisms:
EpinephrineACTHFSHLH
Extracellular fluid
Cytoplasm
GDP
GlucagonPTHTSHCalcitonin
1
2
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Copyright © 2010 Pearson Education, Inc. Figure 16.2, step 3
Hormone (1st messenger)binds receptor.
Receptoractivates Gprotein (GS).
G proteinactivatesadenylatecyclase.
Receptor
G protein (GS)
Adenylate cyclase
Hormones thatact via cAMPmechanisms:
EpinephrineACTHFSHLH
Extracellular fluid
Cytoplasm
GDP
GlucagonPTHTSHCalcitonin
1
2 3
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Copyright © 2010 Pearson Education, Inc. Figure 16.2, step 4
Hormone (1st messenger)binds receptor.
Receptoractivates Gprotein (GS).
G proteinactivatesadenylatecyclase.
Adenylatecyclaseconverts ATPto cAMP (2ndmessenger).
Receptor
G protein (GS)
Adenylate cyclase
Hormones thatact via cAMPmechanisms:
EpinephrineACTHFSHLH
Extracellular fluid
Cytoplasm
GDP
GlucagonPTHTSHCalcitonin
1
2 3 4
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Copyright © 2010 Pearson Education, Inc. Figure 16.2, step 5
Hormone (1st messenger)binds receptor.
Receptoractivates Gprotein (GS).
G proteinactivatesadenylatecyclase.
cAMP acti-vates proteinkinases.
Adenylatecyclaseconverts ATPto cAMP (2ndmessenger).
Receptor
G protein (GS)
Adenylate cyclase
Triggers responses oftarget cell (activatesenzymes, stimulatescellular secretion,opens ion channel,etc.)
Hormones thatact via cAMPmechanisms:
EpinephrineACTHFSHLH
Inactiveprotein kinase
Extracellular fluid
Cytoplasm
Activeproteinkinase
GDP
GlucagonPTHTSHCalcitonin
1
2 3 4
5
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Intracellular Receptors and Direct Gene Activation• Steroid hormones and thyroid hormone
1.Diffuse into their target cells and bind with intracellular receptors
2.Receptor-hormone complex enters the nucleus
3.Receptor-hormone complex binds to a specific region of DNA
4.This prompts DNA transcription to produce mRNA
5.The mRNA directs protein synthesis
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Copyright © 2010 Pearson Education, Inc. Figure 16.3
mRNA
New protein
DNA
Hormoneresponseelements
Receptor-hormonecomplex
Receptorprotein
Cytoplasm
Nucleus
Extracellular fluid
Steroidhormone
The steroid hormonediffuses through the plasmamembrane and binds anintracellular receptor.
The receptor-hormone complex entersthe nucleus.
The receptor- hormonecomplex binds a hormoneresponse element (aspecific DNA sequence).
Binding initiatestranscription of thegene to mRNA.
The mRNA directsprotein synthesis.
Plasmamembrane
1
2
3
4
5
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Copyright © 2010 Pearson Education, Inc. Figure 16.3, step 1
Receptor-hormonecomplex
Receptorprotein
Cytoplasm
Nucleus
Extracellular fluid
Steroidhormone
The steroid hormonediffuses through the plasmamembrane and binds anintracellular receptor.
Plasmamembrane
1
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Copyright © 2010 Pearson Education, Inc. Figure 16.3, step 2
Receptor-hormonecomplex
Receptorprotein
Cytoplasm
Nucleus
Extracellular fluid
Steroidhormone
The steroid hormonediffuses through the plasmamembrane and binds anintracellular receptor.
The receptor-hormone complex entersthe nucleus.
Plasmamembrane
1
2
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Copyright © 2010 Pearson Education, Inc. Figure 16.3, step 3
DNA
Hormoneresponseelements
Receptor-hormonecomplex
Receptorprotein
Cytoplasm
Nucleus
Extracellular fluid
Steroidhormone
The steroid hormonediffuses through the plasmamembrane and binds anintracellular receptor.
The receptor-hormone complex entersthe nucleus.
The receptor- hormonecomplex binds a hormoneresponse element (aspecific DNA sequence).
Plasmamembrane
1
2
3
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Copyright © 2010 Pearson Education, Inc. Figure 16.3, step 4
mRNA
DNA
Hormoneresponseelements
Receptor-hormonecomplex
Receptorprotein
Cytoplasm
Nucleus
Extracellular fluid
Steroidhormone
The steroid hormonediffuses through the plasmamembrane and binds anintracellular receptor.
The receptor-hormone complex entersthe nucleus.
The receptor- hormonecomplex binds a hormoneresponse element (aspecific DNA sequence).
Binding initiatestranscription of thegene to mRNA.
Plasmamembrane
1
2
3
4
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Copyright © 2010 Pearson Education, Inc. Figure 16.3, step 5
mRNA
New protein
DNA
Hormoneresponseelements
Receptor-hormonecomplex
Receptorprotein
Cytoplasm
Nucleus
Extracellular fluid
Steroidhormone
The steroid hormonediffuses through the plasmamembrane and binds anintracellular receptor.
The receptor-hormone complex entersthe nucleus.
The receptor- hormonecomplex binds a hormoneresponse element (aspecific DNA sequence).
Binding initiatestranscription of thegene to mRNA.
The mRNA directsprotein synthesis.
Plasmamembrane
1
2
3
4
5
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Target Cell Specificity
• Target cells must have specific receptors to which the hormone binds• ACTH receptors are only found on certain cells
of the adrenal cortex
• Thyroxin receptors are found on nearly all cells of the body
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Target Cell Activation
• Target cell activation depends on three factors
1. Blood levels of the hormone
2. Relative number of receptors on or in the target cell
3. Affinity of binding between receptor and hormone
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Target Cell Activation
• Hormones influence the number of their receptors• Up-regulation—target cells form more
receptors in response to the hormone
• Down-regulation—target cells lose receptors in response to the hormone
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Hormones in the Blood
• Hormones circulate in the blood either free or bound• Steroids and thyroid hormone are attached to plasma
proteins
• All others circulate without carriers
• The concentration of a circulating hormone reflects: • Rate of release
• Speed of inactivation and removal from the body
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Hormones in the Blood
• Hormones are removed from the blood by• Degrading enzymes
• Kidneys
• Liver
• Half-life—the time required for a hormone’s blood level to decrease by half
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Interaction of Hormones at Target Cells
• Multiple hormones may interact in several ways• 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
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Control of Hormone Release
• Blood levels of hormones• Are controlled by negative feedback systems• Vary only within a narrow desirable range
• Hormones are synthesized and released in response to1. Humoral stimuli2. Neural stimuli3. Hormonal stimuli
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Humoral Stimuli
• Changing blood levels of ions and nutrients directly stimulates secretion of hormones
• Example: Ca2+ 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
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Copyright © 2010 Pearson Education, Inc. Figure 16.4a
(a) Humoral Stimulus
Capillary (lowCa2+ in blood)
Parathyroidglands
Thyroid gland(posterior view)
PTHParathyroidglands
1 Capillary blood containslow concentration of Ca2+,which stimulates…
2 …secretion ofparathyroid hormone (PTH)by parathyroid glands*
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Neural Stimuli
• Nerve fibers stimulate hormone release• Sympathetic nervous system fibers stimulate
the adrenal medulla to secrete catecholamines
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Copyright © 2010 Pearson Education, Inc. Figure 16.4b
(b) Neural Stimulus
CNS (spinal cord)
Medulla ofadrenalgland
Preganglionicsympatheticfibers
Capillary
1 Preganglionic sympatheticfibers stimulate adrenalmedulla cells…
2 …to secrete catechola-mines (epinephrine andnorepinephrine)
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Hormonal Stimuli
• Hormones stimulate other endocrine organs to release their hormones • Hypothalamic hormones stimulate the release
of most anterior pituitary hormones• Anterior pituitary hormones stimulate targets to
secrete still more hormones• Hypothalamic-pituitary-target endocrine organ
feedback loop: hormones from the final target organs inhibit the release of the anterior pituitary hormones
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Copyright © 2010 Pearson Education, Inc. Figure 16.4c
(c) Hormonal Stimulus
Hypothalamus
Thyroidgland
Adrenalcortex
Gonad(Testis)
Pituitarygland
1 The hypothalamus secreteshormones that…
2 …stimulatethe anteriorpituitary glandto secretehormonesthat…
3 …stimulate other endocrineglands to secrete hormones