endocrine system 16 a
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Copyright 2010 Pearson Education, Inc.
C h a p t e r
16
The Endocrine
System
PowerPoint Lecture Slidesprepared by Jason LaPres
Lone Star College - North Harris
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Introduction to the Endocrine System
Figure 161 Organs and Tissues of the Endocrine System.
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Introduction to the Endocrine System
Figure 161 Organs and Tissues of the Endocrine System.
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Introduction to the Endocrine System
The Endocrine System Regulates long-term processes
Growth
Development
Reproduction
Uses chemical messengers to relay information and
instructions between cells
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Homeostasis and Intercellular Communication
Direct Communication Exchange of ions and molecules between adjacent
cells across gap junctions
Occurs between two cells of same type
Highly specialized and relatively rare
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Homeostasis and Intercellular Communication
Paracrine Communication
Uses chemical signals to transfer information from
cell to cell within single tissue
Most common form of intercellularcommunication
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Homeostasis and Intercellular Communication
Endocrine Communication
Endocrine cells release chemicals (hormones) into
bloodstream
Alters metabolic activities of many tissues and
organs simultaneously
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Homeostasis and Intercellular Communication
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Homeostasis and Intercellular Communication
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Hormones
Can be divided into three groups
Amino acid derivatives
Peptide hormones
Lipid derivatives
Circulate freely or bound to transport proteins
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Hormones
Figure 162 A Structural Classification of Hormones
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Secretion and Distribution of
Hormones Free Hormones
Remain functional for less than 1 hour
Diffuse out of bloodstream:
bind to receptors on target cells
Are broken down and absorbed:
by cells of liver or kidney
Are broken down by enzymes:
in plasma or interstitial fluids
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Secretion and Distribution of
Hormones Thyroid and Steroid Hormones
Remain in circulation much longer
Enter bloodstream
More than 99% become attached to special transport proteins
Bloodstream contains substantial reserve of bound hormones
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Mechanisms of Hormone Action
Hormone Receptor Is a protein molecule to which a particular molecule binds
strongly
Responds to several different hormones
Different tissues have different combinations of receptors
Presence or absence of specific receptor determines
hormonal sensitivity
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Mechanisms of Hormone Action
Hormones and Plasma Membrane Receptors
Catecholamines and peptide hormones
Are not lipid soluble
Unable to penetrate plasma membrane Bind to receptor proteins at outer surface of plasma
membrane (extracellular receptors)
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Mechanisms of Hormone Action
Hormones and Plasma Membrane Receptors
Bind to receptors in plasma membrane
Cannot have direct effect on activities inside target
cell
Use intracellular intermediary to exert effects
First messenger:
leads to second messenger
may act as enzyme activator, inhibitor, or cofactor
results in change in rates of metabolic reactions
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Mechanisms of Hormone Action
Important Second Messengers
Cyclic-AMP (cAMP)
Derivative of ATP
Cyclic-GMP (cGMP) Derivative of GTP
Calcium ions
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Mechanisms of Hormone Action
The Process ofAmplification
Is the binding of a small number of hormone
molecules to membrane receptors
Leads to thousands of second messengers in cell Magnifies effect of hormone on target cell
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Mechanisms of Hormone Action
Down-regulation Presence of a hormone triggers decrease in number of
hormone receptors
When levels of particular hormone are high, cells become
less sensitive
Up-regulation
Absence of a hormone triggers increase in number of
hormone receptors
When levels of particular hormone are low, cells become
more sensitive
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Mechanisms of Hormone Action
Hormones and Plasma Membrane Receptors
G Protein
Enzyme complex coupled to membrane receptor
Involved in link between first messenger and second messenger
Binds GTP
Activated when hormone binds to receptor at membrane surface
and changes concentration of second messenger cyclic-AMP
(cAMP) within cell:
increased cAMP level accelerates metabolic activity within cell
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Mechanisms of Hormone Action
Figure 163 G Proteins and Hormone Activity.
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Mechanisms of Hormone Action
Figure 163 G Proteins and Hormone Activity.
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Mechanisms of Hormone Action
G Proteins and Calcium Ions Activated G proteins trigger
opening of calcium ion channels in membrane
release of calcium ions from intracellular stores
G protein activates enzyme phospholipase C (PLC)
Enzyme triggers receptor cascade:
production ofdiacylglycerol (DAG) and inositol triphosphate (IP3)
from membrane phospholipids
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Mechanisms of Hormone Action
Figure 163 G Proteins and Hormone Activity.
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Mechanisms of Hormone Action
Hormones and Intracellular Receptors
Alter rate of DNA transcription in nucleus
Change patterns of protein synthesis
Directly affect metabolic activity and structure of
target cell
Includes steroids and thyroid hormones
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Mechanisms of Hormone Action
Figure 164a Effects of Intracellular Hormone Binding.
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Mechanisms of Hormone Action
Figure 164b Effects of Intracellular Hormone Binding.