Facts on File Encyclopedia of Health and Medicine

• ANTIDIURETIC HORMONE(ADH), which the pituitary
  gland stores and releases to regulate the
  amount of water the KIDNEYSretain in the blood
  as one of the body’s mechanisms for controlling
  blood pressure


• CORTICOTROPIN-RELEASING HORMONE(CRH), which
  stimulates the pituitary gland to release
  ADRENOCORTICOTROPIN HORMONE(ACTH) as the first
  level in the body’s STRESS RESPONSE HORMONAL
  CASCADE


• DOPAMINE, which inhibits pituitary gland pro-
  duction of FOLLICLE-STIMULATING HORMONE(FSH),
  LEUTEINIZING HORMONE (LH), THYROID-STIMULATING
  HORMONE(TSH), and PROLACTIN


• GONADOTROPIN-RELEASING HORMONE(GNRH), which
  stimulates the pituitary gland to synthesize and
  release LH and FSH, hormones that are funda-
  mental to reproduction


• GROWTH HORMONE–RELEASING HORMONE (GHRH),
  which stimulates the pituitary gland to synthe-
  size and release GROWTH HORMONE(GH)


• OXYTOCIN, which the pituitary gland subse-
  quently stores and releases when needed to
  stimulate contractions of the UTERUS during
  CHILDBIRTHand to influence sexual arousal in
  both men and women


• THYROTROPIN-RELEASING HORMONE (TRH), which
  stimulates the pituitary gland to synthesize and
  release TSH, initiating hormonal regulation of
  vital functions such as thermal regulation and
  cellular METABOLISM, and to produce prolactin,
  which stimulates milk production during
  BREASTFEEDING

Structure of the Hypothalamus
Despite the vital and extensive nature of its func-
tions, the hypothalamus is physically a small
structure not quite the size and shape of an
almond. Within the hypothalamus are a number
of functionally distinct substructures, called
nuclei, each having unique and specific roles that
require intimate integration with one another.
The major nuclei that have endocrine functions
are the

• supraoptic nucleus, which synthesizes and
  releases ADH
  
  
  • paraventricular nucleus, which synthesizes and
    releases oxytocin, CRH, and TRH
  
  
  • arcuate nucleus, which synthesizes and releases
    GHRH
  
  
  • suprachiasmatic nucleus (SCN), which influ-
    ences the circadian cycle and various body
    rhythms through the cyclic release of certain
    hormones
  
  
  • ventromedial nucleus, which regulates APPETITE
  
  
  
  

Disorders and dysfunctions of the hypothalamus

are extremely rare, and when they do occur tumors

are the most likely cause. Disorders and dysfunc-

tions of other endocrine glands can affect the ways

those glands respond to hypothalamic hormones.

Long-term, chronic ALCOHOLabuse destroys hypo-

thalamic cells, affecting the endocrine and neuro-

logic functions of the hypothalamus.

HYPOTHALAMIC HORMONES

ANTIDIURETIC HORMONE(ADH) CORTICOTROPIN-RELEASING

DOPAMINE HORMONE(CRH)

GONADOTROPIN-RELEASING GROWTH HORMONE–RELEASING

HORMONE(GNRH) HORMONE(GHRH)

OXYTOCIN SOMATOSTATIN

THYROTROPIN-RELEASING

HORMONE(TRH)

For further discussion of the hypothalamus

within the context of the endocrine system’s

structure and function please see the overview

section “The Endocrine System.” For further dis-

cussion of the hypothalamus within the context of

neurologic structures and functions please see the

overview section “The Neurologic System.”

See also ADRENAL GLANDS; OBESITY; PINEAL GLAND;

THYMUS; THYROID GLAND.

hypothyroidism A condition in which the THY-

ROID GLANDsecretes an insufficient amount of thy-

roid hormones. It is the most common disorder of

thyroid function, affecting about 7 million Ameri-

cans. Women are eight times more likely than

men to have hypothyroidism. Risk for hypothy-

roidism increases among men and women with

advancing age. Health experts estimate 80 percent

of people over age 70 have hypothyroidism,

though the rate of diagnosis is not this high.

hypothyroidism 145