Encyclopedia of Health and Medicine

pituitary gland 155
Researchers believe the pineal gland produces
other hormones and has functions related to
immune activity, though what they are remains
unknown.
In the philosophies and traditions of Eastern
medicine, the pineal gland is the metaphysical
“third eye.” Modern researchers have discovered
that the pineal gland does in fact receive NERVE
signals via the OPTIC NERVE and a structure of the
hypothalamus called the suprachiasmatic nucleus
(SCN). These signals influence the pineal gland’s
synthesis of melatonin, which slows when the
external environment is light and accelerates with
the external environment is dark.
Dysfunctions of the pineal gland are, as far as
endocrinologists know, very rare. Some research
has established a link between low melatonin levels
and breast cancer, though further research
continues to examine this connection. Researchers
are also exploring possible connections between
pineal function and insomnia (difficulty sleeping).
For further discussion of the pineal gland
within the context of the endocrine system’s
structure and function please see the overview
section “The Endocrine System.”
See also SLEEP DISORDERS.
pituitary gland An ENDOCRINE GLAND located
within the BRAIN that secretes the hormones that
regulate the activity of the other endocrine structures,
except the HYPOTHALAMUS, in the body. A distinctively
glandular structure, gray in color and
somewhat egg shaped, the pituitary gland nestles
into a hollow of BONE at the base of the skull
directly beneath the hypothalamus. This physical
proximity makes possible a dedicated network of
BLOOD vessels that carry hormones from the hypothalamus
directly to the pituitary gland, allowing a
continuous flow of chemical messages.
The pituitary gland has two lobes, the anterior
lobe and the posterior lobe. The posterior lobe
stores hormones it receives from the hypothalamus
and releases them when hypothalamic signals
it to do so. The anterior lobe produces hormones
essential for growth and maturation. The hormones
of the pituitary gland are peptide hormones.
Disorders of the pituitary gland affect
FERTILITY, growth, and METABOLISM.
Anterior Lobe Structure and Hormones
The anterior lobe of the pituitary gland, also called
the adenohypophysis, is under the hormonal control
of the hypothalamus. The hormones the anterior
lobe of the pituitary gland synthesizes include
• ADRENOCORTICOTROPIN HORMONE (ACTH), which
signals the ADRENAL GLANDS to release CORTISOL,
EPINEPHRINE, and NOREPINEPHRINE
• GROWTH HORMONE (GH), which stimulates growth
during childhood by increasing the rate at
which cells divide and helps maintain MUSCLE
mass in adulthood
• THYROID-STIMULATING HORMONE (TSH), which stimulates
the THYROID GLAND to release the primary
thyroid hormones THYROXINE (T 4 ) and TRI-
IODOTHYRONINE (T 3 )
• FOLLICLE-STIMULATING HORMONE (FSH), which initiates
egg maturation in the OVARIES and SPERM
production in the TESTES
• LUTEINIZING HORMONE (LH), which stimulates egg
release in the ovaries and TESTOSTERONE secretion
from the testes
• PROLACTIN, which stimulates milk production
during BREASTFEEDING
These hormones all initiate hormonal cascades
among other endocrine structures. Negative-feedback
loops regulate the amounts of hormones the
pituitary gland secretes, with secretions slowing or
stopping when terminal hormones reach appropriate
levels in the blood circulation. The hormones
of the anterior pituitary are integral to the
body’s STRESS RESPONSE HORMONAL CASCADE.
HORMONES OF THE ANTERIOR PITUITARY LOBE
ADRENOCORTICOTROPIN
HORMONE (ACTH)
LUTEINIZING HORMONE (LH)
THYROID-STIMULATING
HORMONE (TSH)
FOLLICLE-STIMULATING HORMONE
(FSH)
GROWTH HORMONE (GH)
PROLACTIN
Posterior Lobe Structure and Hormones
The posterior lobe of the pituitary gland, also
called the neurohypophysis, receives the hormones
ANTIDIURETIC HORMONE (ADH) and OXYTOCIN
from the hypothalamus and then stores them. The