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2. The endocrine system is made of
many glands—groups of cells that
release chemical substances called
hormones into the bloodstream.
Hormones influence and regulate
diverse activities such as
metabolism, growth, mental
development, and emotional
behavior.

3. The parathyroid glands are four small glands located in
the neck behind the thyroid gland. These glands secrete
a hormones that regulate the body’s use of calcium and
phosphorus to maintain healthy bones. Parathyroid
hormone also affects muscle contraction and the
conduction of nerve impulses.

4. The pituitary gland is a pea-sized gland located
in the center of the skull. The pituitary gland
acts as a master controlling gland, releasing a
number of hormones that activate other
glands.

5. The thyroid gland, located in the neck, secretes the hormone
thyroxine. Thyroxine increases body metabolism, in which food
is broken down and converted into heat and energy. Too little
thyroxine in the blood produces lethargy and fatigue, while too
much thyroxine results in overactivity, nervousness, and
weight loss.

6. The adrenals are two small glands, each located on the top of one kidney. These
two glands consist of an inner core, called the adrenal medulla, and an outer
area, known as the adrenal cortex. The adrenal medulla releases the hormone
epinephrine, which speeds up heart rate and increases blood pressure to help
the body cope with emergencies. The adrenal cortex releases hormones that
control the level of salts and water in the blood and help regulate the use of
sugar. It also secretes small amounts of male sex hormones, or androgens, in
both males and females. Of the two parts of the adrenal glands, only the adrenal
cortex is under the control of the pituitary gland.

7. The pancreas is a long, narrow gland located in the
abdomen behind the stomach and beneath the liver. The
pancreas secretes insulin, a hormone that regulates the
body’s use of sugar. When too little insulin is produced,
the body tissues cannot use or store sugar, and a disease
known as diabetes mellitus develops.

8. Females have sex glands called ovaries that release hormones
called estrogens. These hormones contribute to the
development of female sexual characteristics, including skin,
hair, and breast development. Estrogens work with certain
pituitary hormones to control the menstrual cycle.

9. Males have sex glands called testes that secrete
androgens, male sex hormones. In addition to
contributing to male sexual characteristics, androgens
contribute to the production of sperm and the
development of the prostate gland.