The stre ss re sp o n se • Figure 9.2 0
By secreting norepinephrine and various hypothalamic releasing factors, the sympathetic nervous
system and hypothalamus coordinate the secretions of other glands and activation of various pro-
cesses to make an immediate and sustained response to stress. (Green arrows represent nervous
activity, red arrows represent primary hormone secretions, and black arrows indicate subsequent
hormone secretions.)
Stressors
stimulate
CRH
GHRH
TRH
ACTH
ACTH
I
Nerve
impulses
Sympathetic centers
in spinal cord
Hypothalamus
Sympathetic nerves
Adrenal
medulla
Adrenal
cortex
SH
hGH
Anterior
pituitary
Visceral effectors
CRH = Corticotropin-releasing hormone
ACTH = Adrenocorticotropic hormone
GHRH = Growth hormone-releasing hormone
hGH = Human growth hormone
TRH = Thyrotropin-releasing hormone
TSH = Thyroid-stimulating hormone
Epinephrine
and
norepinephrine
Supplement
and prolong
“fight-or-flight”
responses
Cortisol
Insulin-like Growth
Factors (IGFs)
Thyroid hormones
(T3 and T4)
>
f
T
T
T
Stress responses
Stress responses mobilize energy resources:
Increased heart rate
• Liver - continues to break down glycogen into glucose and to make
and force of beat
glucose from amino acids and lactic acid. Glucose gets released into the
Constriction of blood
blood. Makes glucose from pyruvic acid, glyceraldehyde-3-phosphate,
vessels of most
lactic acid, glycerol, and certain amino acid substrates (gluconeogenesis
viscera and skin
- see Chapter 14).
Dilation of blood
• Adipose tissue - continues breaking down triglycerides into fatty acids,
vessels of heart,
which get released into blood.
lungs, brain, and
• Skeletal muscle - breaks down protein into amino acids, which get
skeletal muscles
released into the blood.
Contraction of spleen
Thyroid hormones stimulate cells to make use of glucose, fatty acids,
Conversion of glycogen
into glucose in liver
Sweating
Dilation of airways
Decrease in digestive
activities
Water retention and
elevated blood pressure
and amino acids to make ATP.
a.
“ Fight-or-flight” responses
b. Resistance reaction
276 CHAPTER 9
The Endocrine System
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