2.4 The Endocrine System


LOQ 2-6 How does the endocrine system transmit information and interact with the nervous system?

endocrine [EN-duh-krin] system the body’s “slow” chemical communication system; a set of glands that secrete hormones into the bloodstream.

hormones chemical messengers that are manufactured by the endocrine glands, travel through the bloodstream, and affect other tissues.

So far, we have focused on the body’s speedy electrochemical information system. But your body has a second communication system, the endocrine system (FIGURE 2.8). Glands in this system secrete hormones, another form of chemical messenger. Hormones travel through our bloodstream and influence many aspects of our life—growth, reproduction, metabolism, and mood.

Figure 2.8: FIGURE 2.8 The endocrine system

Some hormones are chemically identical to neurotransmitters. The endocrine system and nervous system are therefore close relatives. Both produce molecules that act on receptors elsewhere. Like many relatives, they also differ. The speedier nervous system zips messages from eyes to brain to hand in a fraction of a second. Endocrine messages trudge along in the bloodstream, taking several seconds or more to travel from the gland to the target tissue. The nervous system transmits information to specific receptor sites with text-message speed. The endocrine system is more like delivering an old-fashioned letter.

adrenal [ah-DREEN-el] glands a pair of endocrine glands that sit just above the kidneys and secrete hormones (epinephrine and norepinephrine) that help arouse the body in times of stress.

But slow and steady sometimes wins the race. The effects of endocrine messages tend to outlast those of neural messages. Have you ever felt angry long after the cause of your angry feelings was resolved (say, your friend apologized for her rudeness)? You may have experienced an “endocrine hangover” from lingering emotion-related hormones. Angry feelings can hang on, even when we’ve chosen to move past them. When this happens, we need a little time to simmer down. Consider what happens behind the scenes when you hear burglar-like noises outside your window. Your ANS may order your adrenal glands to release epinephrine and norepinephrine (also called adrenaline and noradrenaline). In response, your heart rate, blood pressure, and blood sugar will rise, giving you a surge of energy known as the fight-or-flight response. When the “burglar” turns out to be a playful friend, the hormones—and your alert, aroused feelings—will linger a while.

pituitary gland the most influential endocrine gland. Under the influence of the hypothalamus, the pituitary regulates growth and controls other endocrine glands.

The endocrine glands’ control center is the pituitary gland. This pea-sized structure, located in the brain’s core, is controlled by a nearby brain area, the hypothalamus (more on that shortly). The pituitary releases a number of hormones. One is a growth hormone that stimulates physical development. Another is oxytocin, which enables contractions during birthing, milk flow in nursing, and orgasm. Oxytocin also promotes social interactions. When couples bond, or when we experience feelings of group togetherness or social trust, oxytocin’s pleasant presence is paving the way (De Dreu et al., 2010; Zak, 2012).


Pituitary secretions also direct other endocrine glands to release their hormones. The pituitary, then, is a master gland (whose own master is the hypothalamus). For example, under the brain’s influence, the pituitary triggers your sex glands to release sex hormones. These in turn influence your brain and behavior.

This feedback system (brain → pituitary → other glands → hormones → body and brain) reveals the interplay between the nervous and endocrine systems. The nervous system directs endocrine secretions, which then affect the nervous system. In charge of this whole electrochemical orchestra is that master conductor we call the brain.

Retrieve + Remember

Question 2.9

Why is the pituitary gland called the “master gland”?

ANSWER: Responding to signals from the hypothalamus, the pituitary releases hormones that trigger other endocrine glands to secrete hormones, which in turn influence our brain and our behavior.

Question 2.10

How are the nervous and endocrine systems alike, and how do they differ?

ANSWER: Both of these communication systems produce chemical molecules that act on the body’s receptors to influence our behavior and emotions. The endocrine system, which secretes hormones into the bloodstream, delivers its messages much more slowly than the speedy nervous system, and the effects of the endocrine system’s messages tend to linger much longer than those of the nervous system.