1. © 2015 Pearson Education, Inc.
The Endocrine System
Similar in fxn to the Nervous System
Both send a message-Δ fxn of cell
Nervous System-quick on, quick off
Endocrine System-slow on, slow off
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2. Figure 18-1 Organs and Tissues of the Endocrine System (Part 1 of 2).
Hypothalamus
Pineal Gland
Production of ADH, OXT, and regulatory hormones
Melatonin
Parathyroid Glands
Pituitary Gland
(located on the posterior surface of the thyroid gland)
Anterior lobe
ACTH, TSH, GH, PRL, FSH, LH, and MSH
Parathyroid hormone (PTH)
Posterior lobe
Release of oxytocin (OXT)
and antidiuretic hormone (ADH)
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3. Figure 18-1 Organs and Tissues of the Endocrine System (Part 2 of 2).
Organs with Secondary Endocrine Functions
Heart
See Chapter 21
• Atrial natriuretic peptide (ANP)
Thyroid Gland
• Brain natriuretic peptide (BNP)
Thyroxine (T4) Triiodothyronine (T3)
Calcitonin (CT)
Thymus (Undergoes atrophy during adulthood)
See Chapter 22
• Thymosins
Adrenal Gland
Adipose Tissue
Medulla
• Leptin
Epinephrine (E) Norepinephrine (NE)
Digestive Tract
See Chapter 25
Cortex
Secretes numerous hormones involved in the coordination of system functions, glucose metabolism, and appetite
Cortisol, corticosterone, aldosterone, androgens
Pancreatic Islets
Kidneys
See Chapters 19 and 26
• Erythropoietin (EPO) • Calcitriol
Insulin, glucagon
Gonads
See Chapters 28 and 29
KEY TO PITUITARY HORMONES
Testes (male) Androgens (especially testosterone), inhibin
ACTH Adrenocorticotropic hormone
TSH Thyroid-stimulating hormone
Testis
GH Growth hormone
PRL Prolactin
FSH Follicle-stimulating hormone
Ovaries (female) Estrogens, progesterone, inhibin
Ovary
LH Luteinizing hormone
MSH Melanocyte-stimulating hormone
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Hormone: organic chemical that changes the function of its target cell
Autocrine-
Paracrine-
Endocrine-
exocrine
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Maintenance of Homeostasis
Water/electrolytes
Enzyme function
Transport
Regulate long term processes
Development
Growth
Reproduction
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Circulate freely-don’t last long
Bind to receptor
b.d. by liver or kidneys
b.d. by enzymes in plasma or interstitial fluid
Bound to a carrier-last a long time
Reserves in the blood stream
Once released from carrier-don’t last long
Same reasons as above
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7. © 2015 Pearson Education, Inc.
Hormones
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8. Figure 18-4a Effects of Intracellular Hormone Binding.
Steroid hormones diffuse through the plasma membrane and bind to receptors in the cytoplasm or nucleus. The complex then binds to DNA in the nucleus, activating specific genes. 1
Diffusion through membrane lipids
Target cell response
CYTOPLASM
Alteration of cellular structure or activity 6
Translation and protein synthesis
Receptor 2
Binding of hormone to cytoplasmic or nuclear receptors 5
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Transcription and mRNA production
Receptor 4
Gene activation
Nuclear pore 3
Nuclear envelope
Binding of hormone–receptor complex to DNA

9. Figure 18-4b Effects of Intracellular Hormone Binding.
Thyroid hormones enter the cytoplasm and bind to receptors in the nucleus to activate specific genes. They also bind to receptors on mitochondria and accelerate ATP production. 1
Transport across plasma membrane
Target cell response
Target cell response
Increased
Alteration of cellular structure or activity
ATP
production
Receptor 6
Translation and protein synthesis 2
Binding of receptors at mitochondria and nucleus 5
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Transcription and mRNA production
Receptor 4
Gene activation 3
Binding of hormone–receptor complex to DNA

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11. Figure 18-3 G Proteins and Second Messengers (Part 1 of 2).
The first messenger (a peptide hormone, catecholamine, or eicosanoid) binds to a membrane receptor and activates a G protein.
A G protein is an enzyme complex coupled to a membrane receptor that serves as a link between the first and second messenger.
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Hormone
Hormone
Protein receptor
Protein receptor
G protein (inactive)
G protein activated
Effects on cAMP Levels
Many G proteins, once activated, exert their effects by changing the concentration of cyclic AMP, which acts as the second messenger within the cell.
Hormone
Hormone
Protein receptor
Protein receptor
G protein activated
Increased production of cAMP
G protein activated
Enhanced breakdown of cAMP
Acts as second messenger
adenylate cyclase
PDE
cAMP
ATP
cAMP
AMP
kinase
Reduced enzyme activity
Opens ion channels
Activates enzymes
If levels of cAMP increase, enzymes may be activated or ion channels may be opened, accelerating the metabolic activity of the cell.
In some instances, G protein activation results in decreased levels of cAMP in the cytoplasm. This decrease has an inhibitory effect on the cell.
First Messenger Examples • Epinephrine and norepinephrine (β receptors) • Calcitonin • Parathyroid hormone • ADH, ACTH, FSH, LH, TSH
First Messenger Examples • Epinephrine and norepineph- rine (α2 receptors)

12. Figure 18-3 G Proteins and Second Messengers (Part 2 of 2).
The first messenger (a peptide hormone, catecholamine, or eicosanoid) binds to a membrane receptor and activates a G protein.
A G protein is an enzyme complex coupled to a membrane receptor that serves as a link between the first and second messenger.
615
Hormone
Hormone
Protein receptor
Protein receptor
G protein (inactive)
G protein activated
Effects on Ca2+ Levels
Some G proteins use Ca2+ as a second messenger.
Ca2+
Hormone
Protein receptor
G protein activated
PLC, DAG, and IP3
Opening of Ca2+ channels
Release of stored Ca2+ from ER or SER
Ca2+
Ca2+
Ca2+ acts as second messenger
Ca2+
Calmodulin
Activates enzymes
First Messenger Examples
• Epinephrine and norepinephrine (α1 receptors)
• Oxytocin
• Regulatory hormones of hypothalamus • Several eicosaoids

13. A&P Flix Animation: Mechanism of Hormone Action: Second Messenger cAMP

14. Mechanisms of Hormone Action
The Process of Amplification
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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15. 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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16. Figure 18-3 G Proteins and Second Messengers (Part 1 of 2).
The first messenger (a peptide hormone, catecholamine, or eicosanoid) binds to a membrane receptor and activates a G protein.
A G protein is an enzyme complex coupled to a membrane receptor that serves as a link between the first and second messenger.
615
Hormone
Hormone
Protein receptor
Protein receptor
G protein (inactive)
G protein activated
Effects on cAMP Levels
Many G proteins, once activated, exert their effects by changing the concentration of cyclic AMP, which acts as the second messenger within the cell.
Hormone
Hormone
Protein receptor
Protein receptor
G protein activated
Increased production of cAMP
G protein activated
Enhanced breakdown of cAMP
Acts as second messenger
adenylate cyclase
PDE
cAMP
ATP
cAMP
AMP
kinase
Reduced enzyme activity
Opens ion channels
Activates enzymes
If levels of cAMP increase, enzymes may be activated or ion channels may be opened, accelerating the metabolic activity of the cell.
In some instances, G protein activation results in decreased levels of cAMP in the cytoplasm. This decrease has an inhibitory effect on the cell.
First Messenger Examples • Epinephrine and norepinephrine (β receptors) • Calcitonin • Parathyroid hormone • ADH, ACTH, FSH, LH, TSH
First Messenger Examples • Epinephrine and norepineph- rine (α2 receptors)

17. © 2015 Pearson Education, Inc.
615
© 2015 Pearson Education, Inc.

18. Figure 18-3 G Proteins and Second Messengers (Part 2 of 2).
The first messenger (a peptide hormone, catecholamine, or eicosanoid) binds to a membrane receptor and activates a G protein.
A G protein is an enzyme complex coupled to a membrane receptor that serves as a link between the first and second messenger.
615
Hormone
Hormone
Protein receptor
Protein receptor
G protein (inactive)
G protein activated
Effects on Ca2+ Levels
Some G proteins use Ca2+ as a second messenger.
Ca2+
Hormone
Protein receptor
G protein activated
PLC, DAG, and IP3
Opening of Ca2+ channels
Release of stored Ca2+ from ER or SER
Ca2+
Ca2+
Ca2+ acts as second messenger
Ca2+
Calmodulin
Activates enzymes
First Messenger Examples
• Epinephrine and norepinephrine (α1 receptors)
• Oxytocin
• Regulatory hormones of hypothalamus • Several eicosaoids

19. © 2015 Pearson Education, Inc.
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20. © 2015 Pearson Education, Inc.
Endocrine Reflexes
Endocrine Reflexes
Functional counterparts of neural reflexes
In most cases, controlled by negative feedback mechanisms
Stimulus triggers production of hormone whose effects reduce intensity of the stimulus
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21. © 2015 Pearson Education, Inc.
Endocrine Reflexes
Endocrine reflexes can be triggered by
Humoral stimuli
Changes in composition of extracellular fluid
Hormonal stimuli
Arrival or removal of specific hormone
Neural stimuli
Arrival of neurotransmitters at neuroglandular junctions
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22. © 2015 Pearson Education, Inc.
Endocrine Reflexes
Simple Endocrine Reflex
Involves only one hormone
Controls hormone secretion by the heart, pancreas, parathyroid gland, and digestive tract
Complex Endocrine Reflex
Involves
One or more intermediary steps
Two or more hormones
The hypothalamus
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23. Figure 18-5 Three Mechanisms of Hypothalamic Control over Endocrine Function
Production of ADH
and oxytocin
Secretion of regulatory
hormones to control activity
of the anterior lobe of the
pituitary gland
Control of sympathetic
output to adrenal
medullae
HYPOTHALAMUS
Preganglionic
motor fibers
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Adrenal cortex
Infundibulum
Adrenal medulla
Posterior lobe
of pituitary gland
Anterior lobe
of pituitary gland
Adrenal gland
Hormones secreted by the anterior
lobe control other endocrine organs
Release of ADH
and oxytocin
Secretion of epinephrine
and norepinephrine 23

24. © 2015 Pearson Education, Inc.
Endocrine Reflexes
Neuroendocrine Reflexes
Pathways include both neural and endocrine components
Complex Commands
Issued by changing
Amount of hormone secreted
Pattern of hormone release:
hypothalamic and pituitary hormones released in sudden bursts
frequency changes response of target cells
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