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Chapter 15 Part I Overview
Hormone types
Hormone activity
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Endocrine System Function
• Control cell activity
• metabolism
• Release hormones
• Slower control than CNS/PNS
• Endocrine glands: pituitary, thyroid, parathyroid, adrenal, and pineal glands
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Endocrine System: Overview
• Some organs have endocrine and exocrine function
• pancreas and gonads
• adipose cells, thymus, small intestine, stomach, kidneys, and heart
• Hypothalamus has neural and endocrine functions
Copyright © 2011 Pearson Education, Inc. Figure 15.1
Pineal glandHypothalamus
Pituitary 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 ranging chemical signals, travel through blood or lymph
• Autocrine: chemicals affect the cells that secretes them
• “self stimulating”
• Paracrine: locally acting chemicals that affect other cells
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Hormone Action
• How hormones cause change:
1. Open or close ion channels
2. Stimulate synthesis of proteins
3. Activate or deactivate enzymes
4. Induce secretion
5. Stimulate mitosis
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Chemistry of Hormones
• Two main classes
1. Amino acid-based hormones
• Water soluble
• ex. Proteins… such as tryptophan
2. Steroids
• Non-water soluble
• Made from cholesterol
• ex. Estrogen & testosterone
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Mechanisms of Hormone Action
Two mechanisms, depends on chemical makeup
1. Water-soluble hormones (amino acid–based)
• Cannot enter target cells
• Can’t pass through plasma membrane
• Bind to receptors on cell surface
• Initiate chain reactions inside cell
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Membrane Receptors and Second-Messengers
• Hormone signaling mechanism
1. Hormone (primary messenger) binds to surface receptor
2. Receptor activates internal signals(secondary messengers)
3. Triggers change in the cell
• Increased mitosis
• Protein production
Copyright © 2011 Pearson Education, Inc. Figure 15.2, step 1
Hormone (1st messenger)binds receptor.
Receptor
Hormones thatact via cAMPmechanisms:
EpinephrineACTHFSHLH
Extracellular fluid
Cytoplasm
GlucagonPTHTSHCalcitonin
1
Figure 15.2, 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
Figure 15.2, 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
Figure 15.2, step 4
Hormone (1st messenger)binds receptor.
Receptor
G protein (GS)
Adenylate cyclase
Hormones thatact via cAMPmechanisms:
EpinephrineACTHFSHLH
Extracellular fluid
Cytoplasm
GDP
GlucagonPTHTSHCalcitonin
1
2 3 4
Figure 15.2, step 5
Hormone (1st messenger)binds receptor.
cAMP acti-vates proteinkinases.Receptor
G protein (GS)
Adenylate cyclase
Triggers responses of target cell (activates enzymes, stimulates cellular secretion, opens ion channel,etc.)
Hormones thatact via cAMPmechanisms:
EpinephrineACTHFSHLH
Inactiveprotein
Extracellular fluid
Cytoplasm
Activeprotein
GDP
GlucagonPTHTSHCalcitonin
1
4
5
• cAMP is a common second messenger.
Copyright © 2011 Pearson Education, Inc.
Mechanisms of Hormone Action
2. Lipid-soluble hormones (steroids)
• Can pass through plasma membrane
• Bind to intracellular receptors
• Directly activates gene
• Receptor + hormone binds to DNA
• Promotes transcription of mRNA
• mRNA then translated into protein
Copyright © 2011 Pearson Education, Inc. Figure 15.3, step 1
Receptor-hormonecomplex
Receptorprotein
Cytoplasm
Nucleus
Extracellular fluid
Steroidhormone
The steroid hormonediffuses through the plasmamembrane and binds anintracellular receptor.
Plasmamembrane
1
Figure 15.3, 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
Figure 15.3, 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
Figure 15.3, 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
Figure 15.3, 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 Activation
• Target cell activation depends on:
1. Presence of receptor
• Target cells must have specific hormone receptors
• Receptors are often limited to specific tissues
2. Hormone concentration
3. Number of receptors on cell
4. binding of receptor and hormone
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Target Cell Activation
• Hormones can influence receptor numbers
• Up-regulation —more receptors
• Down-regulation — lose receptors
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Control of Hormone Release
• Negative feedback loops
• Help control hormone release
• Hormones produced inhibit upstream glands
• ex. To make hormone 3 you need hormones 1 and 2.
• Negative feedback loop is hormone 3 inhibits production of hormones 1 and 2.
• Prevents overproduction of hormones
Copyright © 2011 Pearson Education, Inc. Figure 15.4c
Hypothalamus
Thyroidgland
Adrenalcortex
Gonad(Testis)
Pituitarygland
1 The hypothalamus secreteshormones that…
2 …stimulatethe anteriorpituitary glandto secretehormonesthat…
3 …stimulate other endocrineglands to secrete hormones
Neg
ativ
e fe
edba
ckNegative Feedback Loop