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Chapter 45
HORMONES AND THE ENDOCRINE
SYSTEM
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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 are equipped to respond.
• Insect metamorphosis and many other processes
are regulated by hormones.
• P.S. – Plants have hormones too
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Overview: continued…
• 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.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Hormones trigger specific responses
• Chemical signals bind to receptor proteins
on target cells.
• Only target cells respond to the signal.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Types of Secreted Signaling Molecules
• Secreted chemical signals include:
–
–
–
–
–
Hormones
Local regulators
Neurotransmitters
Neurohormones
Pheromones
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
What is a Hormone?
• Endocrine chemicals secreted into extracellular
fluids and travel in the bloodstream.
• Endocrine glands are ductless and secrete
hormones directly into surrounding fluid.
• Hormones mediate responses to environmental
stimuli and regulate growth, development, and
reproduction.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 45-2a
Blood
vessel
Response
(a) Endocrine signaling
Response
(b) Paracrine signaling
Response
(c) Autocrine signaling
Not all Glands are Endocrine.
• Exocrine glands have ducts and secrete
substances onto body surfaces or into body
cavities (for example, tear ducts).
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Local Regulators
• Local regulators are chemical signals that
travel over short distances by diffusion.
• Local regulators help regulate blood pressure,
nervous system function, and reproduction.
• Local regulators are divided into two types:
– Paracrine signals act on cells near the secreting cell
– Autocrine signals act on the secreting cell itself
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 45-2a
Blood
vessel
Response
(a) Endocrine signaling
Response
(b) Paracrine signaling
Response
(c) Autocrine signaling
Neurotransmitters and Neurohormones
• Neurons (nerve cells) contact target cells at
synapses.
• Neurons secrete chemical signals called
neurotransmitters that diffuse a short distance
across the synapse to bind to receptors on the
target cell.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 45-2b
Synapse
Neuron
Response
(d) Synaptic signaling
Neurosecretory
cell
Blood
vessel
(e) Neuroendocrine signaling
Response
Neurohormones:
• Are a class of hormones that originate from
neurons in the brain and diffuse through the
bloodstream.
• Endorphins are an example.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 45-2b
Synapse
Neuron
Response
(d) Synaptic signaling
Neurosecretory
cell
Blood
vessel
(e) Neuroendocrine signaling
Response
Pheromones
• Pheromones - chemical signals that are
released from the body and used to
communicate with other individuals in the
species.
• Pheromones are “outside” the body.
• Pheromones - mark trails to food sources,
warn of predators, and attract potential mates.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Classes and properties of hormones
• The solubility of a hormone correlates with
the location of receptors inside or on the
surface of target cells.
• Lipid-soluble hormones (steroid hormones)
pass easily through cell membranes, while
water-soluble hormones (polypeptides and
amines) do not.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 45-3
Water-soluble
Lipid-soluble
0.8 nm
Polypeptide:
Insulin
Steroid:
Cortisol
Amine:
Epinephrine
Amine:
Thyroxine
Cellular Response Pathways
• 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.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Cell Signaling:
• Signaling by any of these hormones
involves three key events:
– Reception
– Signal transduction
– Response
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 45-5-1
Fat-soluble
hormone
Watersoluble
hormone
Signal receptor
Transport
protein
TARGET
CELL
(a)
Signal
receptor
NUCLEUS
(b)
Fig. 45-5-2
Fat-soluble
hormone
Watersoluble
hormone
Transport
protein
Signal receptor
TARGET
CELL
Cytoplasmic
response
OR
Signal
receptor
Gene
regulation
Cytoplasmic
response
(a)
NUCLEUS
(b)
Gene
regulation
Water soluble example:
• 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.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 45-6-1
Epinephrine
Adenylyl
cyclase
G protein
G protein-coupled
receptor
GTP
ATP
cAMP
Second
messenger
Fig. 45-6-2
Epinephrine
Adenylyl
cyclase
G protein
G protein-coupled
receptor
GTP
ATP
cAMP
Inhibition of
glycogen synthesis
Promotion of
glycogen breakdown
Protein
kinase A
Second
messenger
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.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 45-7-1
Hormone
(estradiol)
Estradiol
(estrogen)
receptor
Plasma
membrane
Hormone-receptor
complex
Fig. 45-7-2
Hormone
(estradiol)
Estradiol
(estrogen)
receptor
Plasma
membrane
Hormone-receptor
complex
DNA
Vitellogenin
mRNA
for vitellogenin
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
– Different proteins for carrying out the response
• A hormone can also have different effects in
different species.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Negative feedback and antagonistic
hormone pairs are common features
of the endocrine system
• Hormones are assembled into regulatory
pathways.
• Feedback loops are commonly used.
• Hormones are often arranged in pairs that work
against each other.
• Blood sugar regulation and calcium deposition
in bones are common test examples.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings