C H A P T E R 3 4
Introduction to the endocrine system
515
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As the “master gland” of the neuroendocrine system,
the hypothalamus helps to regulate the central and
autonomic nervous systems and the endocrine system
to maintain homeostasis.
■■
The hypothalamus produces stimulating and
inhibiting factors that travel to the anterior pituitary
to stimulate the release of pituitary hormones or
block the production of certain pituitary hormones
when levels of target hormones get too high.
■■
The hypothalamus is connected to the posterior
pituitary by a nerve network that delivers the
hypothalamic hormones ADH and oxytocin
KEY POINTS
to be stored in the posterior pituitary until the
hypothalamus stimulates their release.
THE PITUITARY GLAND
The
pituitary gland
is located in the skull in the bony
sella turcica under a layer of dura mater. It is divided
into three lobes: an anterior lobe, a posterior lobe and an
intermediate lobe. Traditionally, the anterior pituitary
was known as the body’s master gland because it has so
many important functions and, through feedback mech
anisms, regulates the function of many other endocrine
glands. In addition, its unique and protected position in
Internal
stimuli
Hypothalamus
External
stimuli
Kidney
Uterus
FSH-LH
ADH
ACTH
TSH
Prolactin
Bone
GH
Oxytocin
Posterior
pituitary
Anterior
pituitary
Releasing and inhibiting
factors GHRH, somatostatin,
CRH, TRH, GnRH, PRH, PIF
Blood levels of hormones
regulate hypothalamus and
anterior pituitary
Corpus
luteum
Ovary
Testes
Testosterone
Adrenocorticoid
hormone
Thyroid
hormone
Thyrotropin
works here
Progesterone
Oestrogen
Adrenal
Thryoid
Breast
Breast
FIGURE 34.1
The traditional endocrine system. The hypothalamus secretes releasing factors to stimulate the parathyroid gland to produce
stimulating factors that enter the circulation and react with specific target glands, which produce endocrine hormones.
