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.
In general, the endocrine system is in charge of body processes that happen
slowly, such as cell growth. Faster processes like breathing and body movement
are monitored by the nervous system. But even though the nervous system and
endocrine system are separate systems, they often work together to help the body
function properly.
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. Some
types of glands release their secretions in specific areas. For instance,
exocrine (pronounced: ek-suh-krin) glands, such as the
sweat and salivary glands, release secretions in the skin or inside of the
mouth. 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.
Although the endocrine glands are the body's main hormone producers, some
non-endocrine organs - such as the brain, heart, lungs, kidneys, liver, thymus,
skin, and placenta - also produce and release hormones.
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 production and secretion of
pituitary hormones can be influenced by factors such as emotions and seasonal
changes. To accomplish this, the hypothalamus relays information sensed by the
brain (such as environmental temperature, light exposure patterns, and feelings)
to the pituitary.
The tiny pituitary is divided into two parts: the anterior lobe and the
posterior lobe. The anterior lobe regulates the activity of the thyroid,
adrenals, and reproductive glands. Among the hormones it produces are:
- growth hormone
, which stimulates the growth of bone and other body
tissues and plays a role in the body's handling of nutrients and minerals
- prolactin
(pronounced: pro-lak-tin), which activates milk
production in women who are breastfeeding
- thyrotropin
(pronounced: thigh-ruh-tro-pin), which stimulates
the thyroid gland to produce thyroid hormones
- corticotropin
(pronounced: kor-tih-ko-tro-pin), which
stimulates the adrenal gland to produce certain hormones
The pituitary also secretes endorphins (pronounced:
en-dor-finz), chemicals that act on the nervous system to reduce
sensitivity to pain. In addition, the pituitary secretes hormones that signal
the ovaries and testes to make sex hormones. The pituitary gland also controls
ovulation and the menstrual cycle in women.
The posterior lobe of the pituitary releases antidiuretic
(pronounced: an-ty-dy-uh-reh-tik) hormone, which helps control
body water balance through its effect on the kidneys and urine output; and
oxytocin (pronounced: ahk-see-toe-sin), which triggers the
contractions of the uterus that occur during labor.
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