is a protein, and as its name suggests, it pro-
motes milk production. No normal physiological role in
human males has been f
rmly established, although prolac-
tin may help maintain normal sperm production. In contrast,
abnormally elevated levels oF the hormone can disrupt sex-
ual Function in both sexes.
Prolactin secretion is mostly under inhibitory control
by dopamine From the hypothalamus, also called
release inhibiting hormone
(PIH). The hypothalamus likely
releases more than one
Growth hormone can stimulate elongation oF bone tissue
directly, but its eFFect on cartilage requires a mediator substance,
insulin-like growth Factor-1 (IG±-1). Growth hormone releases
IG±-1 From the liver and other tissues. Clinical Application 13.2
discusses some clinical uses oF growth hormone.
that secrete posterior
cells that secrete
Posterior lobe of pituitary gland
Sella turcica of
Anterior lobe of pituitary gland
Hypothalamic releasing hormones stimulate cells of the anterior lobe to secrete hormones. Nerve impulses originating in the
hypothalamus stimulate nerve endings in the posterior lobe of the pituitary gland to release hormones.
Peripheral endocrine gland
Light micrograph of the anterior pituitary gland (240×).
Hypothalamic control of the peripheral endocrine
glands may use as many as three types of hormones, with multiple
negative feedback controls. (