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 NERVEand 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 lev-
els 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 BRAINthat secretes the hormones that
regulate the activity of the other endocrine struc-
tures, except the HYPOTHALAMUS, in the body. A dis-
tinctively glandular structure, gray in color and
somewhat egg shaped, the pituitary gland nestles
into a hollow of BONEat the base of the skull
directly beneath the hypothalamus. This physical
proximity makes possible a dedicated network of
BLOODvessels that carry hormones from the hypo-
thalamus 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 hypothala-
mus and releases them when hypothalamic signals
it to do so. The anterior lobe produces hormones
essential for growth and maturation. The hor-
mones of the pituitary gland are peptide hor-
mones. 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 con-
trol of the hypothalamus. The hormones the ante-
rior lobe of the pituitary gland synthesizes include- ADRENOCORTICOTROPIN HORMONE (ACTH), which
signals the ADRENAL GLANDSto 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 stim-
ulates the THYROID GLANDto release the primary
thyroid hormones THYROXINE (T 4 ) and TRI-
IODOTHYRONINE(T 3 ) - FOLLICLE-STIMULATING HORMONE(FSH), which initi-
ates egg maturation in the OVARIESand SPERM
production in the TESTES - LUTEINIZING HORMONE(LH), which stimulates egg
release in the ovaries and TESTOSTERONEsecre-
tion from the testes - PROLACTIN, which stimulates milk production
during BREASTFEEDING
These hormones all initiate hormonal cascades
among other endocrine structures. Negative-feed-
back loops regulate the amounts of hormones the
pituitary gland secretes, with secretions slowing or
stopping when terminal hormones reach appro-
priate levels in the blood circulation. The hor-
mones of the anterior pituitary are integral to the
body’s STRESS RESPONSE HORMONAL CASCADE.HORMONES OF THE ANTERIOR PITUITARY LOBE
ADRENOCORTICOTROPIN FOLLICLE-STIMULATING HORMONE
HORMONE(ACTH)(FSH)
LUTEINIZING HORMONE(LH) GROWTH HORMONE(GH)
THYROID-STIMULATING PROLACTIN
HORMONE(TSH)Posterior Lobe Structure and Hormones
The posterior lobe of the pituitary gland, also
called the neurohypophysis, receives the hor-
mones ANTIDIURETIC HORMONE(ADH) andOXYTOCIN
from the hypothalamus and then stores them. Thepituitary gland 155