hoW does groWth hormone affect bodily
groWth?- Growth hormone (GH) stimulates the growth of bone and skeletal
muscle, among other tissues. - Excessive GH causes faster-than-normal bone growth that leads
to gigantism in children and acromegaly in adults. A deficiency
during childhood can cause pituitary dwarfism.
taKe-home messagen Growth hormone (GH) is so important to normal bodily
growth that major abnormalities develop when it does not
function properly.n Links to Bone development 5.1, Skeletal muscles 6.1
Growth hormone from the anterior pituitary affects target
cells throughout the body. It acts indirectly, by triggering
the synthesis of a growth factor, mainly in the liver. One
major GH effect is stimulating the growth of cartilage and
bone and increasing muscle mass. You may recall from
Chapter 5 that GH prevents the epiphyseal plates at the
ends of growing long bones from hardening during child-
hood and adolescence. Because this hormone has such
major effects on bodily growth, if the pituitary secretes too
much or too little of it, the impact can be profound.
For instance, gigantism results when the anterior lobe
of the pituitary overproduces it during childhood. This
is what happened to Sultan Kosen, the unusually tall
man pictured at the beginning of this chapter. Like him,
affected adults are proportionally like an average-sized
person but much larger. If too much GH is secreted during
adulthood, bones, cartilage, and other connective tissues in
the hands, feet, and jaws thicken abnormally. So do epithe-
lia of the skin, nose, eye lids, lips, and tongue. The result is
acromegaly (Figure 15.5A and 15.5B). Both gigantism and
acromegaly usually develop as the result of a benign (non-
cancerous) pituitary tumor.
Pituitary dwarfism occurs when the pituitary makes
too little GH or when receptors cannot respond normally
to it. Affected people are quite short but have normal
proportions. Pituitary dwarfism can be inherited (Figure
15.5C) or it can result from a pituitary tumor or injury.
Human growth hormone is now made through genetic
engineering (Chapter 21). Children who have a naturally
low GH level may receive injections of recombinant human
growth hormone (rhGH), although the treatment is expen-
sive (up to $20,000 a year) and controversial. Some physi-
cians and ethicists object to short stature being treated as a
defect to be cured.
Injections of rhGH are also used to treat adults who
have a low GH level as the result of an injury or a tumor
of the pituitary or hypothalamus. The injection can help
maintain healthy bone and muscle mass while reducing
body fat. Entrepreneurs and others have touted rhGH
injections as a means to slow normal aging or boost
athletic performance. Thus far, clinical trials don’t bear
out this claim, and the drug is not approved for those uses.
Negative side effects include increased risk of high blood
pressure and diabetes.15.5 GH Growth Functions and Disorders
Figure 15.5 Disorders in bodily growth may result from too much or too
little growth hormone. a A woman before and after she became affected
by acromegaly. Notice how her jaw (chin) became elongated as the disorder
progressed. b Skull X-ray showing the jutting jaw of an adult who has
acromegaly. c Dr. Hiralal Maheshwari, right, with two men from a village in
Pakistan where an inherited form of pituitary dwarfism is common. Men of
the village average a little over 4 feet (130 cm) tall.c
© Courtesy of G. Baumann, M.D., Northwestern UniversityA: © Courtesy of Dr. William H. Daughaday, Washington University School of Medicine, from A.I. Mendelhoff and D.E. Smith, eds., American Journal of Medicine, 20:133 (1956); B: Zephyr/Science Sourcea Age 16 Age 52 bthe endOCrIne system 293Copyright 2016 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s).