Pineal Body
The pineal body, or pineal gland, is located in the middle of the brain. It
secretes a hormone called melatonin, which may help regulate the wake-
sleep cycle of the body.
The endocrine system is made up of glands that produce and secrete
hormones, chemical substances produced in the body that regulate the
activity of cells or organs. These hormones regulate the body's growth,
metabolism (the physical and chemical processes of the body), and sexual
development and function. The hormones are released into the bloodstream
and may affect one or several organs throughout the body.
Hormones are chemical messengers created by the body. They transfer
information from one set of cells to another to coordinate the functions of
different parts of the body.
The major glands of the endocrine system are the hypothalamus, pituitary,
thyroid, parathyroids, adrenals, pineal body, and the reproductive organs
(ovaries and testes). The pancreas is also a part of this system; it has a role in
hormone production as well as in digestion.
The endocrine system is regulated by feedback in much the same way that a
thermostat regulates the temperature in a room. For the hormones that are
regulated by the pituitary gland, a signal is sent from the hypothalamus to the
pituitary gland in the form of a "releasing hormone," which stimulates the
pituitary to secrete a "stimulating hormone" into the circulation. The
stimulating hormone then signals the target gland to secrete its hormone. As
the level of this hormone rises in the circulation, the hypothalamus and the
pituitary gland shut down secretion of the releasing hormone and the
stimulating hormone, which in turn slows the secretion by the target gland.
This system results in stable blood concentrations of the hormones that are
regulated by the pituitary gland.
Hormones Regulated by the Hypothalamic/Pituitary System
Pituitary Stimulating Hypothalamic Releasing
Hormone
Hormone Hormone
Thyroid Thyroid-stimulating Thyrotropin-releasing hormone
Hormones Regulated by the Hypothalamic/Pituitary System
Pituitary Stimulating Hypothalamic Releasing
Hormone
Hormone Hormone
hormones T4,
hormone (TSH) (TRH)
T3
Adrenocorticotropin Corticotropin-releasing factor
Cortisol
hormone (ACTH) (CRF)
Luteinizing hormone-releasing
Follicle-stimulating
Estrogen or hormone (LHRH) or
hormone (FSH),
testosterone gonadotropin-releasing
luteinizing hormone (LH)
hormone (GnRH)
Insulinlike
Growth hormone-releasing
growth factor-I Growth hormone
hormone (GHRH)
(IGF-I)
Hypothalamus
The hypothalamus is located in the lower central part of the brain. This part of
the brain is important in regulation of satiety, metabolism, and body
temperature. In addition, it secretes hormones that stimulate or suppress the
release of hormones in the pituitary gland. Many of these hormones are
releasing hormones, which are secreted into an artery (the hypophyseal portal
system) that carries them directly to the pituitary gland. In the pituitary gland,
these releasing hormones signal secretion of stimulating hormones. The
hypothalamus also secretes a hormone called somatostatin, which causes the
pituitary gland to stop the release of growth hormone.
Pituitary Gland
The pituitary gland is located at the base of the brain beneath the
hypothalamus and is no larger than a pea. It is often considered the most
important part of the endocrine system because it produces hormones that
control many functions of other endocrine glands. When the pituitary gland
does not produce one or more of its hormones or not enough of them, it is
called hypopituitarism.
The pituitary gland is divided into two parts: the anterior lobe and the posterior
lobe. The anterior lobe produces the following hormones, which are regulated
by the hypothalamus:
Growth hormone: Stimulates growth of bone and tissue (Growth
hormone deficiency results in growth failure. Growth hormone
deficiency in adults results in problems in maintaining proper amounts
of body fat and muscle and bone mass. It is also involved in emotional
well-being.)
Thyroid-stimulating hormone (TSH): Stimulates the thyroid gland to
produce thyroid hormones (A lack of thyroid hormones either because
of a defect in the pituitary or the thyroid itself is called hypothyroidism.)
Adrenocorticotropin hormone (ACTH): Stimulates the adrenal gland
to produce several related steroid hormones
Luteinizing hormone (LH) and follicle-stimulating hormone
(FSH): Hormones that control sexual function and production of the
sex steroids, estrogen and progesterone in females or testosterone in
males
Prolactin: Hormone that stimulates milk production in females
The posterior lobe produces the following hormones, which are not regulated
by the hypothalamus:
Antidiuretic hormone (vasopressin): Controls water loss by the
kidneys
Oxytocin: Contracts the uterus during childbirth and stimulates milk
production
The hormones secreted by the posterior pituitary are actually produced in the
brain and carried to the pituitary gland through nerves. They are stored in the
pituitary gland.
