c. Acromegaly
A tumor of the anterior pituitary after puberty causes
excess secretion of human growth hormone, resulting
in acromegaly, a condition in which long bones can
no longer grow. Instead, the bones of the hands, feet,
face, and jaw thicken and grow larger.
Pituitary dwarfism, gigantism, and
acromegaly are caused by abnormal levels
of secretion of human growth hormone • Figure 9.5
b. Gigantism
A tumor of the anterior pitu-
itary existing prior to puberty
causes secretion of too much
human growth hormone, result-
ing in gigantism. The accel-
eration of bone growth in this
condition results in a person
with normal proportions but
taller-than-normal height.
a. Pituitary Dwarfism
When the levels of secretion of hu-
man growth hormone (hGH) by the
anterior pituitary are insufficient
prior to puberty, bone growth is
impaired and the individual does
not grow to normal height. A person
with pituitary dwarfism has nor-
mal body proportions but overall
shorter-than-normal height.
When the anterior pituitary secretes either too little or
too much human growth hormone (hGH), several disorders
are manifested. These include pituitary dwarfism (Figure
9.5a), gigantism (Figure 9.5b) and acromegaly (Figure
9.5c). Abnormal secretions that result in dwarfism or gigan-
tism usually occur prior to puberty, while acromegaly results
from abnormal secretions after puberty. When a tumor is the
cause of excess secretion, the condition may be treated with
either surgery or chemotherapy to shrink the tumor.
The anterior pituitary may be involved in endocrine
disorders of other endocrine glands. We will discuss these
diseases when we discuss those glands.
Hypothalamic neurosecretory cells make and secrete
oxytocin through the posterior pituitary. Oxytocin influ-
ences birth and milk release (lactation). During birth, oxy-
tocin stimulates muscle contractions in the uterus. After
birth, oxytocin stimulates milk release or let-down from
breast tissue when the infant suckles.
The Endocrine System
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