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messengers, hormones, which travel through the bloodstream and affect other tissues,
including the brain. When hormones act on the brain, they influence our interest in sex,
food, and aggression.
PRACTICE Some hormones are chemically identical to neurotransmitters (the chemical messen-
gers that diffuse across a synapse and excite or inhibit an adjacent neuron). The endocrine
Argumentation (SP 4) system and nervous system are therefore close relatives: Both produce molecules that act
on receptors elsewhere. But like many family members, they also differ. The speedier ner-
(Out of class) Have students vous system zips messages from eyes to brain to hand in a fraction of a second. Meanwhile,
research disorders of the endocrine endocrine messages trudge along in the bloodstream, taking several seconds or more to
system (e.g., diabetes, abnormal travel from the gland to the target tissue. If the nervous system transmits information with
text-message speed, the endocrine system delivers an old-fashioned letter.
growth, and hypothyroidism and But slow and steady sometimes wins the race. Endocrine messages tend to outlast the
hyperthyroidism). Ask them to use effects of neural messages. Have you ever felt angry long after the cause of your angry
scientifically derived evidence to feelings was resolved (say, your friend apologized for their rudeness)? You may have experi-
enced an “endocrine hangover” from lingering emotion-related hormones.
support their claims as they answer In a moment of danger, the ANS orders the adrenal glands on top of the kidneys to
the following questions: release epinephrine and norepinephrine (also called adrenaline and noradrenaline). These hor-
mones increase heart rate, blood pressure, and blood sugar, providing a surge of energy to
• What physical and emotional power our fight-or-flight response. When the emergency passes, the hormones — and the
feelings — linger a while.
problems do these disorders The most influential endocrine gland is the pituitary gland, a pea-sized structure located
Distributed by Bedford, Freeman & Worth Publishers. Not for redistribution.
cause? in the core of the brain, where it is controlled by an adjacent brain area, the hypothalamus
®
AP Science Practice (more on that shortly). Among the hormones released by the pituitary is a growth hormone
• What treatments are available for Research that stimulates physical development. Another is oxytocin, which enables orgasm and, in
these disorders? Because it is easily measured women, labor contractions and milk flow while nursing. Oxytocin also aids social support.
Copyright © Bedford, Freeman & Worth Publishers.
through saliva, cortisol level is a While grooming their children, male baboons’ oxytocin levels surge (Rincon et al., 2020).
Use the students’ findings to common operational definition of By promoting social bonding, oxytocin strengthens communities and enables them to act
stress. Revisit Unit 0 if you need a
introduce the concepts related to refresher on variables and opera- cooperatively against threats (Quintana & Guastella, 2020; Zhang et al., 2019).
Pituitary secretions also direct other endocrine glands to release their hormones. The
the endocrine system. tional definitions. pituitary, then, is a maestro gland (whose own director is the hypothalamus). For example,
under the brain’s influence, the pituitary triggers your sex glands to release sex hormones.
These hormones, in turn, influence your brain and behavior (Goetz et al., 2014). So, too,
with stress. A stressful event triggers your hypothalamus to instruct your pituitary to
release a hormone that causes your adrenal glands to flood your body with cortisol, a stress
PRACTICE hormone that increases blood sugar.
Research Methods & Design Prejudice causes stress Research
demonstrates that an experience of
(SP 2) prejudice may trigger release of the
stress hormone cortisol (Deer et al.,
(5 minutes) Students need to be 2018).
familiar with operational definitions.
Because it is easily measured
through saliva, cortisol level is a
common operational definition of
stress. Ask students to think of other hormones chemical messengers
possible operational definitions for that are manufactured by the
endocrine glands, travel through
stress. Answers could include heart the bloodstream, and affect other fizkes/Getty Images
rate, blood pressure, self-report on tissues.
a survey, and so on.
36 Unit 1 Biological Bases of Behavior

TEACH 1.3-4
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Oxytocin in women sparks labor during
Although the glands of the endocrine pregnancy. The hypothalamus is discussed in greater
system are outside the scope of the • The thyroid releases thyroxine and detail in Module 1.4b, but it’s a good idea to
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AP exam, you may want to share the triiodothyronine, increasing metabolic rate, introduce this small but important brain part
following information about the major growth, and maturation. to your students here. The hypothalamus
endocrine glands and the hormones • The parathyroids release parathyroid regulates our entire neurotransmitter and
they secrete with your students: hormone, increasing blood calcium and hormonal system. Have students think of all
• The anterior pituitary gland decreasing potassium. the behaviors and processes regulated by
secretes growth hormone. Too • The pancreas secretes insulin, regulating hormones: reproduction and sexual response,
little produces dwarfism; too much the level of sugar in the bloodstream. hunger and metabolism, the stress response,
results in gigantism. • The ovaries secrete estrogen, promoting and so on.
• The posterior pituitary gland ovulation and female sex characteristics.
secretes vasopressin (in addition • The testes release androgens, promoting
to oxytocin), constricting blood sperm production and male sex
vessels and raising blood pressure. characteristics.

36 Unit 1 Biological Bases of Behavior

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