1. Chapter 45 – Overview: The Body’s Long-Distance Regulators
Animal hormones are chemical signals that are secreted into the circulatory system and communicate regulatory messages within the body
Hormones reach all parts of the body, but only target cells have receptors for that hormone
Insect metamorphosis is regulated by hormones
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2. Two systems coordinate communication throughout the body: the endocrine system and the nervous system
The endocrine system secretes hormones that coordinate slower but longer-acting responses including reproduction, development, energy metabolism, growth, and behavior
The nervous system conveys high-speed electrical signals along specialized cells called neurons; these signals regulate other cells
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3. Concept 45.1: Hormones and other signaling molecules bind to target receptors, triggering specific response pathways
Endocrine signaling is just one of several ways that information is transmitted between animal cells
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4. Intercellular Communication
The ways that signals are transmitted between animal cells are classified by two criteria
The type of secreting cell
The route taken by the signal in reaching its target
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5. Endocrine Signaling
Hormones secreted into extracellular fluids by endocrine cells reach their targets via the bloodstream
Endocrine signaling maintains homeostasis, mediates responses to stimuli, regulates growth and development
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6. Paracrine and Autocrine Signaling
Local regulators are molecules that act over short distances, reaching target cells solely by diffusion
In paracrine signaling, the target cells lie near the secreting cells
In autocrine signaling, the target cell is also the secreting cell
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7. (a) Endocrine signaling
Figure 45.2a
Blood vessel
Response
(a) Endocrine signaling
Response
(b) Paracrine signaling
Figure 45.2 Intercellular communication by secreted molecules.
Response
(c) Autocrine signaling

8. Synaptic and Neuroendocrine Signaling
In synaptic signaling, neurons form specialized junctions with target cells, called synapses
At synapses, neurons secrete molecules called neurotransmitters that diffuse short distances and bind to receptors on target cells
In neuroendocrine signaling, specialized neurosecretory cells secrete molecules called neurohormones that travel to target cells via the bloodstream
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9. (d) Synaptic signaling
Figure 45.2b
Synapse
Neuron
Response
(d) Synaptic signaling
Neurosecretory cell
Figure 45.2 Intercellular communication by secreted molecules.
Blood vessel
Response
(e) Neuroendocrine signaling

10. Endocrine Tissues and Organs
In some tissues, endocrine cells are grouped together in ductless organs called endocrine glands
Endocrine glands secrete hormones directly into surrounding fluid
These contrast with exocrine glands, which have ducts and which secrete substances onto body surfaces or into cavities
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11. Major endocrine glands:
Figure 45.4
Major endocrine glands:
Hypothalamus
Pineal gland
Pituitary gland
Organs containing endocrine cells:
Thyroid gland
Thymus
Parathyroid glands (behind thyroid)
Heart
Liver
Adrenal glands (atop kidneys)
Stomach
Pancreas
Kidneys
Small intestine
Figure 45.4 Major human endocrine glands.
Ovaries (female)
Testes (male)

12. Chemical Classes of Hormones
Three major classes of molecules function as hormones in vertebrates
Polypeptides (proteins and peptides)
Amines derived from amino acids
Steroid hormones
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13. Lipid-soluble hormones (steroid hormones) pass easily through cell membranes, while water-soluble hormones (polypeptides and amines) do not
The solubility of a hormone correlates with the location of receptors inside or on the surface of target cells
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14. Water-soluble (hydrophilic) Lipid-soluble (hydrophobic)
Figure 45.5
Water-soluble (hydrophilic)
Lipid-soluble (hydrophobic)
Polypeptides
Steroids
0.8 nm
Insulin
Cortisol
Amines
Figure 45.5 Hormones differ in structure and solubility.
Epinephrine
Thyroxine

15. Cellular Response Pathways
Water- and lipid-soluble hormones differ in their paths through a body
Water-soluble hormones are secreted by exocytosis, travel freely in the bloodstream, and bind to cell- surface receptors
Lipid-soluble hormones diffuse across cell membranes, travel in the bloodstream bound to transport proteins, and diffuse through the membrane of target cells
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16. Water- soluble hormone Lipid- soluble hormone
Figure
SECRETORY CELL
Water- soluble hormone
Lipid- soluble hormone
VIA BLOOD
Transport protein
Signal receptor
TARGET CELL
Signal receptor
Figure 45.6 Receptor location varies with hormone type.
NUCLEUS
(a)
(b)

17. Pathway for Water-Soluble Hormones
Binding of a hormone to its receptor initiates a signal transduction pathway leading to responses in the cytoplasm, enzyme activation, or a change in gene expression
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18. Epinephrine binds to receptors on the plasma membrane of liver cells
The hormone epinephrine has multiple effects in mediating the body’s response to short-term stress
Epinephrine binds to receptors on the plasma membrane of liver cells
This triggers the release of messenger molecules that activate enzymes and result in the release of glucose into the bloodstream
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19. G protein-coupled receptor GTP
Figure
Epinephrine
Adenylyl cyclase
G protein
G protein-coupled receptor
GTP
ATP
Second messenger
cAMP
Figure 45.7 Cell-surface hormone receptors trigger signal transduction.
Protein kinase A
Inhibition of glycogen synthesis
Promotion of glycogen breakdown

20. Pathway for Lipid-Soluble Hormones
The response to a lipid-soluble hormone is usually a change in gene expression
Steroids, thyroid hormones, and the hormonal form of vitamin D enter target cells and bind to protein receptors in the cytoplasm or nucleus
Protein-receptor complexes then act as transcription factors in the nucleus, regulating transcription of specific genes
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21. Estradiol (estrogen) receptor
Figure
Hormone (estradiol)
EXTRACELLULAR FLUID
Estradiol (estrogen) receptor
Plasma membrane
Hormone-receptor complex
NUCLEUS
CYTOPLASM
Figure 45.8 Steroid hormone receptors directly regulate gene expression.
DNA
Vitellogenin
mRNA for vitellogenin

22. Multiple Effects of Hormones
The same hormone may have different effects on target cells that have
Different receptors for the hormone
Different signal transduction pathways
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23. Same receptors but different intracellular proteins (not shown)
Figure 45.9
Same receptors but different intracellular proteins (not shown)
Different receptors
Different cellular responses
Different cellular responses
Epinephrine
Epinephrine
Epinephrine
 receptor
 receptor
 receptor
Glycogen deposits
Vessel dilates.
Figure 45.9 One hormone, different effects.
Vessel constricts.
Glycogen breaks down and glucose is released from cell.
(a) Liver cell
(b)
Skeletal muscle blood vessel
Intestinal blood vessel
(c)

24. Signaling by Local Regulators
Local regulators are secreted molecules that link neighboring cells or directly regulate the secreting cell
Types of local regulators
Cytokines and growth factors
Nitric oxide (NO)
Prostaglandins
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25. Coordination of Neuroendocrine and Endocrine Signaling
The endocrine and nervous systems generally act coordinately to control reproduction and development
For example, in larvae of butterflies and moths, the signals that direct molting originate in the brain
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26. Concept 45.2: Feedback regulation and antagonistic hormone pairs are common in endocrine systems
Hormones are assembled into regulatory pathways
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27. Simple Hormone Pathways
Hormones are released from an endocrine cell, travel through the bloodstream, and interact with specific receptors within a target cell to cause a physiological response
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28. S cells of duodenum secrete the hormone secretin ( ).
Figure 45.11
Pathway
Example 
Stimulus
Low pH in duodenum
S cells of duodenum secrete the hormone secretin ( ).
Endocrine cell
Hormone
Negative feedback
Blood vessel
Figure A simple endocrine pathway.
Target cells
Pancreas
Response
Bicarbonate release

29. Hypothalamus/ posterior pituitary
Figure 45.12
Pathway
Example 
Stimulus
Suckling
Sensory neuron
Hypothalamus/ posterior pituitary
Posterior pituitary secretes the neurohormone oxytocin ( ).
Neurosecretory cell
Positive feedback
Neurohormone
Blood vessel
Figure A simple neuroendocrine pathway.
Target cells
Smooth muscle in breasts
Response
Milk release

30. Feedback Regulation
A negative feedback loop inhibits a response by reducing the initial stimulus, thus preventing excessive pathway activity
Positive feedback reinforces a stimulus to produce an even greater response
For example, in mammals oxytocin causes the release of milk, causing greater suckling by offspring, which stimulates the release of more oxytocin
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31. Insulin and Glucagon: Control of Blood Glucose
Insulin (decreases blood glucose) and glucagon (increases blood glucose) are antagonistic hormones that help maintain glucose homeostasis
The pancreas has clusters of endocrine cells called pancreatic islets with alpha cells that produce glucagon and beta cells that produce insulin
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32. Body cells take up more glucose. Insulin
Figure 45.13
Body cells take up more glucose.
Insulin
Beta cells of pancreas release insulin into the blood.
Liver takes up glucose and stores it as glycogen.
STIMULUS: Blood glucose level rises (for instance, after eating a carbohydrate-rich meal).
Blood glucose level declines.
Homeostasis: Blood glucose level (70–110 mg/m100mL)
STIMULUS: Blood glucose level falls (for instance, after skipping a meal).
Figure Maintenance of glucose homeostasis by insulin and glucagon.
Blood glucose level rises.
Liver breaks down glycogen and releases glucose into the blood.
Alpha cells of pancreas release glucagon into the blood.
Glucagon

33. Target Tissues for Insulin and Glucagon
Insulin reduces blood glucose levels by
Promoting the cellular uptake of glucose
Slowing glycogen breakdown in the liver
Promoting fat storage, not breakdown
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34. Glucagon increases blood glucose levels by
Stimulating conversion of glycogen to glucose in the liver
Stimulating breakdown of fat and protein into glucose
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