ENDOCRINE SYSTEM INFORMATION
Although we rarely
think about them, the glands of the endocrine system and the hormones they
release influence almost every cell, organ, and function of our bodies. The
endocrine system is instrumental in regulating mood, growth
and development, tissue function, and metabolism, as well as sexual function
and reproductive processes.
What Is the
Endocrine System?
The
foundations of the endocrine system are the hormones and glands. As the body's
chemical messengers, hormones (pronounced: hor-moanz) transfer
information and instructions from one set of cells to another. Although many
different hormones circulate throughout the bloodstream, each one affects only
the cells that are genetically programmed to receive and respond to its
message. Hormone levels can be influenced by factors such as stress, infection,
and changes in the balance of fluid and minerals in blood.
A gland is a
group of cells that produces and secretes, or gives off, chemicals. A gland
selects and removes materials from the blood, processes them, and secretes the
finished chemical product for use somewhere in the body. Endocrine glands,
on the other hand, release more than 20 major hormones directly into the
bloodstream where they can be transported to cells in other parts of the body.
The major glands
that make up the human endocrine system are the hypothalamus, pituitary,
thyroid, parathyroids, adrenals, pineal body, and the reproductive glands,
which include the ovaries and testes. The pancreas is also part of this
hormone-secreting system, even though it is also associated with the digestive
system because it also produces and secretes digestive enzymes.
The hypothalamus
(pronounced: hi-po-tha-luh-mus), a collection of specialized cells
that is located in the lower central part of the brain, is the primary link
between the endocrine and nervous systems. Nerve cells in the hypothalamus
control the pituitary gland by producing chemicals that either stimulate or
suppress hormone secretions from the pituitary.
Although it is no
bigger than a pea, the pituitary (pronounced: puh-too-uh-ter-ee)
gland, located at the base of the brain just beneath the hypothalamus, is
considered the most important part of the endocrine system. It's often called
the "master gland" because it makes hormones that control several
other endocrine glands. The hypothalamus relays information sensed by the brain
(such as environmental temperature, light exposure patterns, and feelings) to
the pituitary.
The thyroid (pronounced:
thigh-royd), located in the front part of the lower neck, is shaped like
a bowtie or butterfly and produces the thyroid hormones thyroxine
(pronounced: thigh-rahk-seen) and triiodothyronine (pronounced:
try-eye-uh-doe-thigh-ruh-neen). These hormones control the rate at which
cells burn fuels from food to produce energy.
Attached to the
thyroid are four tiny glands that function together called the parathyroids (pronounced:
par-uh-thigh-roydz). They release parathyroid hormone, which
regulates the level of calcium in the blood with the help of calcitonin (pronounced:
kal-suh-toe-nin), which is produced in the thyroid.
The body has two
triangular adrenal (pronounced: uh-dree-nul) glands, one
on top of each kidney. The adrenal glands have two parts, each of which
produces a set of hormones and has a different function. The outer part, the adrenal
cortex, produces hormones called corticosteroids (pronounced:
kor-tih-ko-ster-oydz) that influence or regulate salt and water balance
in the body, the body's response to stress, metabolism, the immune system, and
sexual development and function. The inner part, the adrenal medulla (pronounced:
muh-duh-luh), produces catecholamines (pronounced: kah-tuh-ko-luh-meenz),
such as epinephrine (pronounced: eh-puh-neh-frun). Also called
adrenaline, epinephrine increases blood pressure and heart rate when the body
experiences stress. (Epinephrine injections are often used to counteract a
severe allergic reaction.)
The gonads
are the main source of sex hormones. In males, they are located in the scrotum.
Male gonads, or testes (pronounced: tes-teez), secrete
hormones called androgens (pronounced: an-druh-junz), the most
important of which is testosterone (pronounced: teh-stass-tuh-rone).
These hormones regulate body changes associated with sexual development,
including enlargement of the penis, the growth spurt that occurs during puberty,
and the appearance of other male secondary sex characteristics such as
deepening of the voice, growth of facial and pubic hair.
The female gonads,
the ovaries (pronounced: o-vuh-reez), are located in the pelvis.
They produce eggs and secrete the female hormones estrogen (pronounced: es-truh-jen)
and progesterone (pronounced: pro-jes-tuh-rone). Estrogen is
involved in the development of female sexual features such as breast growth,
the accumulation of body fat around the hips and thighs, and the growth spurt
that occurs during puberty. Both estrogen and progesterone are also involved in
pregnancy and the regulation of the menstrual cycle.
The pancreas
(pronounced: pan-kree-us) produces (in addition to others) two important
hormones, insulin (pronounced: in-suh-lin) and glucagon (pronounced:
gloo-kuh-gawn). They work together to maintain a steady level of
glucose, or sugar, in the blood and to keep the body supplied with fuel to
produce and maintain stores of energy.