Biology of Disease

THE PITUITARY GLAND

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Growth hormone acts on general body tissues to promote growth and
development. Follicle stimulating hormone and LH, collectively referred
to as gonadotrophins, act on the testes and ovaries and are essential for
reproduction. Adrenocorticotrophic hormone acts on the adrenal cortex and
stimulates release of cortisol. Prolactin stimulates the female mammary glands
to control lactation. The release of prolactin is inhibited by dopamine.

The posterior pituitary is composed of a collection of nerve fibers originating
in the hypothalamus. It secretes two main hormones, antidiuretic hormone
(ADH) or vasopressin, and oxytocin although both are made in the
hypothalamus and reach the posterior pituitary in the nerve fibers of the stalk.
The former stimulates the kidneys to conserve water (Chapter 8), whereas the
latter promotes uterine contractions during childbirth and stimulates the
release of milk in breast feeding.

Disorders of Pituitary Function

The majority of disorders in pituitary function are caused by tumors of the
gland although some pituitary diseases can lead to underproduction of its
hormones. Approximately 80% of pituitary tumors are functional, that is
they cause an excessive secretion of hormones. The most common secrete
prolactin, and account for 50% of functional tumors. The incidence of

Figure 7.13 Hypothalamic factors that regulate

anterior pituitary function.

Other

tissues

IGF-I

IGF-I

General

body tissues

Inhibits release

Stimulates release

Insulin-like growth factor I

Hypothalamus

Anterior pituitary

CRH Dopamine GHRH GnRH TRH

ACTH Prolactin GH LH FSH TSH

Thyroid

gland

Adrenal

cortex

Breast Liver Gonads

SR

SR

IR SR SR SR SR

IR