Download Chapter 32- Part I Introduction of Endocrine

CAMPBELL BIOLOGY IN FOCUS
Urry • Cain • Wasserman • Minorsky • Jackson • Reece
32
Homeostasis and
Endocrine Signaling
Lecture Presentations by
Kathleen Fitzpatrick and Nicole Tunbridge
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 Multicellularity allows for cellular specialization with
particular cells devoted to specific activities
 Specialization requires organization and results in
an internal environment that differs from the
external environment
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Organisms must maintain homeostasis.
Why are homeostasis and regulation essential
life functions for living things?
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Homeostasis
 Organisms use homeostasis to maintain a “steady
state” or internal balance regardless of external
environment
 In humans, body temperature, blood pH, and
glucose concentration are each maintained at a
constant level
 Regulation of room temperature by a thermostat is
analogous to homeostasis
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Figure 32.4
Response:
Heating stops.
Room
temperature
decreases.
Sensor/
control center:
Thermostat
turns heater off.
Stimulus:
Room
temperature
increases.
Set point:
Room temperature
at 20C
Stimulus:
Room
temperature
decreases.
Room
temperature
increases.
Response:
Heating starts.
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Sensor/
control center:
Thermostat
turns heater on.
Which body systems are responsible for
maintaining homeostasis in animals?
How are their modes of action different?
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Coordination and Control Functions of the
Endocrine and Nervous Systems
 In the endocrine system, signaling molecules
released into the bloodstream by endocrine cells
reach all locations in the body
 In the nervous system, neurons transmit signals
along dedicated routes, connecting specific locations
in the body
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Figure 32.9
(a) Signaling by hormones (b) Signaling by neurons
Stimulus
Stimulus
Endocrine
cell
Cell
body of
neuron
Nerve
impulse
Hormone
Axon
Signal
travels to
a specific
location.
Signal
travels
everywhere.
Blood
vessel
Nerve
impulse
Axons
Response
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Response
Regulating and Conforming
 Faced with environmental fluctuations, animals
manage their internal environment by either
regulating or conforming
 An animal that is a regulator uses internal
mechanisms to control internal change despite
external fluctuation
 An animal that is a conformer allows its internal
condition to change in accordance with external
changes
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Interpret the following figure.
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Figure 32.3
40
Body temperature (C)
River otter (temperature regulator)
30
20
Largemouth bass
(temperature conformer)
10
0
0
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10
20
30
40
Ambient (environmental) temperature (C)
 An animal may regulate some internal conditions
and not others
 For example, a fish may conform to surrounding
temperature in the water, but it regulates solute
concentrations in its blood and interstitial fluid (the
fluid surrounding body cells)
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How does an organism know if there is a
disruption of homeostasis?
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 Animals achieve homeostasis by maintaining a
variable at or near a particular value, or set point
 Fluctuations above or below the set point serve as
a stimulus; these are detected by a sensor and
trigger a response
 The response returns the variable to the set point
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 Homeostasis in animals relies largely on negative
feedback, a control mechanism that reduces the
stimulus
 Homeostasis moderates, but does not eliminate,
changes in the internal environment
 Set points and normal ranges for homeostasis are
usually stable, but certain regulated changes in the
internal environment are essential
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We need to know a few examples of how
homeostasis is moderated for the AP exam.
Let’s take a closer look…
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Thermoregulation: A Closer Look
 Thermoregulation is the process by which animals
maintain an internal temperature within a tolerable
range
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Describe the difference between endothermic and
ectothermic organisms.
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Endothermy and Ectothermy
 Endothermic animals generate heat by metabolism;
birds and mammals are endotherms = “warmblooded”
 Ectothermic animals gain heat from external
sources; ectotherms include most invertebrates,
fishes, amphibians, and nonavian reptiles = “coldblooded”
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 Endotherms can maintain a stable body
temperature in the face of large fluctuations in
environmental temperature
 Ectotherms may regulate temperature by behavioral
means
 Ectotherms generally need to consume less food
than endotherms, because their heat source is
largely environmental
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How would you classify the following?
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Figure 32.5a
(a) A walrus, an endotherm
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Figure 32.5b
(b) A lizard, an ectotherm
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Balancing Heat Loss and Gain
 Organisms exchange heat by four physical
processes
 Radiation
 Evaporation
 Convection
 Conduction
 Heat is always transferred from an object of higher
temperature to one of lower temperature
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Generate definitions of each type of heat exchange
from the figure.
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Figure 32.6
Radiation
Convection
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Evaporation
Conduction
How might the circulatory system
collaborate in this thermoregulation
process?
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Circulatory Adaptations for Thermoregulation
 In response to changes in environmental
temperature, animals can alter blood (and heat) flow
between their body core and their skin
 Vasodilation, the widening of the diameter of
superficial blood vessels, promotes heat loss
How?
 Vasoconstriction, the narrowing of the diameter of
superficial blood vessels, reduces heat loss
How?
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In aquatic environments, we see adaptations for
how thermoregulation takes place.
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 The arrangement of blood vessels in many marine
mammals and birds allows for countercurrent
exchange
 Countercurrent heat exchangers transfer heat
between fluids flowing in opposite directions and
reduce heat loss
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Figure 32.7
Canada goose
Artery
1
3
Vein
35C
33
30
27
20
18
10
9
Key
Warm blood
Cool blood
Blood flow
Heat transfer
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2
Other mechanisms for
thermoregulation?
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Acclimatization in Thermoregulation
 Birds and mammals can vary their insulation to
acclimatize to seasonal temperature changes
 Acclimatization in ectotherms often includes
adjustments at the cellular level
 Some ectotherms that experience subzero
temperatures can produce “antifreeze” compounds
to prevent ice formation in their cells
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In mammals (FYI: we are mammals, in case you
didn’t know)…
where is the physiological thermostat for
thermoregulation?
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Physiological Thermostats and Fever
 Thermoregulation in mammals is controlled by a
region of the brain called the hypothalamus
 The hypothalamus triggers heat loss or heatgenerating mechanisms
 Fever is the result of a change to the set point for a
biological thermostat
Animation: Negative Feedback
Animation: Positive Feedback
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Figure 32.8a
Sensor/control
center: Thermostat
in hypothalamus
Response: Sweat
Response:
Blood vessels
in skin dilate.
Stimulus:
Increased body
temperature
Body
temperature
decreases.
Homeostasis:
Internal body
temperature of
approximately
36–38C
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Figure 32.8b
Homeostasis:
Internal body
temperature of
approximately
36–38C
Body
temperature
increases.
Stimulus:
Decreased body
temperature
Response:
Blood vessels
in skin constrict.
Response: Shivering
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Sensor/control
center: Thermostat
in hypothalamus
Hormones, released in the endocrine system, are
released to moderate a series of feedback
mechanisms in varying organ systems.
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 Hormones may have effects in a single location or
throughout the body
 Only cells with receptors for a certain hormone can
respond to it
 The endocrine system is well adapted for coordinating
gradual changes that affect the entire body
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We need to know a few examples of endocrine
pathways within the mammalian system.
Let’s take a closer look…
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Simple Endocrine Pathways
 Digestive juices in the stomach are extremely acidic
and must be neutralized before the remaining steps
of digestion take place
 Coordination of pH control in the duodenum relies
on an endocrine pathway
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Figure 32.10
Example
Pathway
Negative feedback

Endocrine
cell
S cells of duodenum
secrete the hormone
secretin ( ).
Hormone
Blood
vessel
Target
cells
Response
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Low pH in
duodenum
Stimulus
Pancreas
Bicarbonate release
 The release of acidic stomach contents into the duodenum
stimulates endocrine cells there to secrete the hormone
secretin
 This causes target cells in the pancreas to raise
the pH in the duodenum
 The pancreas can act as an exocrine gland, secreting
substances through a duct,
Which substances???
or as an endocrine gland, secreting hormones directly
into interstitial fluid
Which hormones???
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Neuroendocrine Pathways
 Hormone pathways that respond to stimuli from the
external environment rely on a sensor in the nervous
system
 In vertebrates, the hypothalamus integrates
endocrine and nervous systems
 Signals from the hypothalamus travel to a gland
located at its base, called the pituitary gland
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Figure 32.11a
Major Endocrine Glands
and Their Hormones
Pineal gland
Melatonin
Thyroid gland
Thyroid hormone
(T3 and T4)
Calcitonin
Parathyroid glands
Parathyroid hormone (PTH)
Ovaries (in females)
Estrogens
Progestins
Testes
(in males)
Androgens
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Hypothalamus
Pituitary gland
Anterior pituitary
Posterior pituitary
Oxytocin
Vasopressin
(antidiuretic
hormone, ADH)
Adrenal glands
(atop kidneys)
Adrenal medulla
Epinephrine and
norepinephrine
Adrenal cortex
Glucocorticoids
Mineralocorticoids
Pancreas
Insulin
Glucagon
Figure 32.11b
Neurosecretory
cells of the
hypothalamus
Hypothalamus
Portal vessels
Hypothalamic
hormones
HORMONE
Posterior
pituitary
Anterior pituitary
Endocrine cells
TARGET
Pituitary hormones
FSH
TSH
ACTH
Prolactin
MSH
GH
Testes or
ovaries
Thyroid
gland
Adrenal
cortex
Mammary
glands
Melanocytes
Liver, bones,
other tissues
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Let’s consider another example…
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Figure 32.11c
Stimulus
TSH circulation
throughout body
Sensory
neuron
Negative feedback
−
Hypothalamus
Thyroid
gland
Neurosecretory cell
TRH
Thyroid
hormone
Thyroid hormone
circulation
throughout
body
−
TSH
Anterior
pituitary
Response
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Figure 32.11d
Low level of
iodine uptake
Thyroid scan
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High level of
iodine uptake
 Hormonal signals from the hypothalamus trigger
synthesis and release of hormones from the
anterior pituitary
 The posterior pituitary is an extension of the
hypothalamus and secretes oxytocin, which
regulates release of milk during nursing in mammals
 It also secretes antidiuretic hormone (ADH)
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Another example…Oxytocin
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Figure 32.12
Example
Pathway

Stimulus
Suckling
Sensory
neuron
Positive feedback
Hypothalamus/
posterior pituitary
Neurosecretory cell
Neurohormone
Target
cells
Response
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Blood
vessel
Posterior
pituitary
secretes the
neurohormone
oxytocin ( ).
Smooth
muscle in
breasts
Milk release
Feedback Regulation in Endocrine Pathways
 A feedback loop links the response back to the
original stimulus in an endocrine pathway
 While negative feedback dampens a stimulus,
positive feedback reinforces a stimulus to increase
the response
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There are different types of hormones
:
water soluble or lipid soluble
Their receptors are located in different places
at their target cells.
They also have very different modes of action.
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Pathways of Water-Soluble and Lipid-Soluble
Hormones
 The hormones discussed thus far are proteins that
bind to cell-surface receptors and that trigger events
leading to a cellular response
 The intracellular response is called signal
transduction
 A signal transduction pathway typically has multiple
steps
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 Lipid-soluble hormones have receptors inside cells
 When bound by the hormone, the hormonereceptor complex moves into the nucleus
 There, the receptor alters transcription of particular
genes
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Multiple Effects of Hormones
 Many hormones elicit more than one type of
response
 For example, epinephrine is secreted by the adrenal
glands and can raise blood glucose levels, increase
blood flow to muscles, and decrease blood flow to the
digestive system
 Target cells vary in their response to a hormone
because they differ in their receptor types or in the
molecules that produce the response
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Figure 32.13
Same receptors but different
intracellular proteins (not shown)
Different cellular responses
Different receptors
Different cellular responses
Epinephrine
Epinephrine
Epinephrine
 receptor
 receptor
 receptor
Glycogen
deposits
Glycogen
breaks down
and glucose
is released
from cell.
(a) Liver cell
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Vessel
dilates.
(b) Skeletal muscle
blood vessel
Vessel
constricts.
(c) Intestinal blood
vessel
Evolution of Hormone Function
 Over the course of evolution the function of a given
hormone may diverge between species
 For example, thyroid hormone plays a role in
metabolism across many lineages, but in frogs it
has taken on a unique function: stimulating the
resorption of the tadpole tail during metamorphosis
 Prolactin also has a broad range of activities in
vertebrates
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Figure 32.14
Tadpole
Adult frog
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