40 PSYCHOLOGY
interacts with the body. Today’s research indicates that the pineal gland secretes a
hormone called melatonin.This hormone plays a role in controlling the bio-
logical timetable for sexual maturation. Another of its functions is to regulate the
sleep cycle.(a) The endocrine glands secrete their substances (without ducts) directly into the
.(b) The pineal gland secretes a hormone called.
Answers: (a) bloodstream; (b) melatonin.The pituitary gland,about the size of a pea, is located in front of the hypo-
thalamus. As already noted, it is called the “master gland” because it secretes a
group of hormones that affect the action of the other glands. Among these hor-
mones there are adrenocorticotrophic hormone (ACTH),a hormone that
acts on the adrenal glands, thyrotrophin,a hormone that acts on the thyroid
gland, and follicle-stimulating hormone,a hormone that acts on the gonads.
One of the hormones secreted by the pituitary gland is growth hormone
(GH).GH has an effect on growth and stature. People who are abnormally tall
have a pathology of the pituitary gland and are said to suffer from the disease of
giantism.
The thyroid glandis located toward the base and front of the neck. It is a rel-
atively large gland and is shaped somewhat like a butterfly. In areas of the world
where the soil is deficient in iodine, some individuals develop a disease of the thy-
roid gland called goiter.The gland can swell to the size of an orange or larger.
One of the reasons that salt is often iodized is to prevent goiter.
The principal function ofthyroxin,the hormone secreted by the thyroid gland,
is to regulate metabolism,the rate at which you burn food. If not enough thyroxin
is secreted, and your metabolic rate is abnormally low, you will tend to gain weight
easily; at a behavioral level you may be sluggish and unenthusiastic. If too much thy-
roxin is secreted, and your metabolic rate is abnormally high, you will have difficulty
gaining weight; at a behavioral level you may be impulsive and hyperactive.(a) What hormone secreted by the pituitary gland is associated with a disease such as
giantism?(b) The principal function of the hormone thyroxin is to regulate.
Answers: (a) Growth hormone (GH); (b) metabolism.There are two adrenal glands,and these are located on top of the kidneys.
The adrenal glands produce such hormones as the corticosteroid hormones and
epinephrine. The corticosteroid hormonesregulate the way the body utilizes
such substances as glucose, salt, and water during times of stress. Epinephrine