The Biological Perspective 65The hormone that controls aspects of pregnancy is called oxytocin, and it is
involved in a variety of ways with both reproduction and parental behavior. It stimu-
lates contractions of the uterus in childbirth. The word itself comes from the Greek word
oxys, meaning “rapid,” and tokos, meaning “childbirth,” and injections of oxytocin are
frequently used to induce or speed up labor and delivery. It is also responsible for the
milk letdown ref lex, which involves contraction of the mammary gland cells to release
milk for the nursing infant. The hormone that controls levels of water in our body is
called vasopressin, and it essentially acts as an antidiuretic, helping the body to conserve
water.
You may have seen oxytocin covered in the news lately, as its role in human social
behavior has been making headlines. Sometimes referred to in the media as the “love
hormone” or the “trust hormone,” it is prompting a great deal of research. While the
role of oxytocin and vasopressin has been demonstrated in the formation of social bonds
in nonhuman animals such as prairie voles, the exact role of these hormones in human
social behavior is still under investigation (Ferguson et al., 2001; Lim & Young, 2006;
Miller, 2013; Stoesz et al., 2013; Winslow et al., 1993).
From investigations of receptor genes to direct impact on social behaviors, both of
these hormones are gathering a lot of attention (Donaldson & Young, 2008; Poulin et al.,
2012; Scheele et al., 2012). One study has suggested men in monogamous relationships
were more likely to keep a greater distance between themselves and an attractive female
during their first meeting after receiving oxytocin (Scheele et al., 2012). The result sug-
gested may help men in heterosexual monogamous relationships remain faithful to their
partners.
There is additional evidence that oxytocin may have different effects for different
individuals under different conditions. Men less socially proficient at recognizing social
cues performed better on a task of empathic accuracy after receiving nasal administra-
tion of oxytocin, whereas more socially proficient males did not (Bartz et al., 2010). Espe-
cially in light of growing interest in the potential role of oxytocin as a treatment for a
variety of psychiatric behaviors where social behavior is impacted (e.g., autism, social
anxiety), researchers need to be aware of the different impacts oxytocin may have on dif-
ferent individuals in different situations (Bartz et al., 2011). Oxytocin’s effects depend on
what people believe about themselves in relation to other people and what they believe
about achieving close social relationships (Bartz et al., 2015). Besides the prosocial affects
most often studied, some researchers have suggested it may be tied more to increasing
the importance of social stimuli. As such, administration of oxytocin has also been tied to
increased aggressive responses (Ne’eman et al., 2016).
Other Endocrine Glands
- 7 Recall the role of various endocrine glands.
As the master gland, the pituitary forms a very important part of a feedback system, one
that includes the hypothalamus and the organs targeted by the various hormones. The
balance of hormones in the entire endocrine system is maintained by feedback from each
of these “players” to the others.
THE PINEAL GLAND The pineal gland is located in the brain, near the back, directly
above the brain stem. It plays an important role in several biological rhythms. The
pineal gland secretes a hormone called melatonin, which helps track day length (and
seasons). In some animals, this influences seasonal behaviors such as breeding and
molting. In humans, melatonin levels are more influential in regulating the sleep–wake
cycle. to Learning Objective 4.3.
THE THYROID GLAND The thyroid gland is located inside the neck and secretes hor-
mones that regulate growth and metabolism. One of these, a hormone called thyroxin,
oxytocin
hormone released by the posterior
pituitary gland that is involved in
reproductive and parental behaviors.
pineal gland
endocrine gland located near the base
of the cerebrum; secretes melatonin.
thyroid gland
endocrine gland found in the neck;
regulates metabolism.