174 MHR • Unit 2 Homeostasis
The differing embryonic origins of the anterior
and posterior lobes are reflected in their
dissimilar functions.The Anterior Pituitary
The anterior lobe of the pituitary gland produces
six types of endocrine hormones, human growth
hormone, and four tropic hormones. The four
tropic hormones made by the anterior pituitary are
the thyroid-stimulating hormone, the follicle
stimulating hormone (FSH), the luteinizing
hormone (LH), and the adrenocorticotropic
hormone (ACTH), all of which will be discussed
later in this chapter.
Human growth hormone The anterior pituitary
regulates growth and development of the body
through the production and secretion of a non-
steroid hormone called human growth hormone
(HGH). Human growth hormone (sometimes referred
to as somatotropin) is a small protein molecule.
HGH spurs body growth by increasing intestinal
absorption of calcium, increasing cell division and
development (especially in bone and cartilage), and
stimulating protein synthesis and lipid metabolism.
HGH triggers the release of fatty acids from fat
cells, and prompts the conversion of fatty acids
into fragments that can then form acetyl CoA for
use as an energy source for the body. HGH also
suppresses glycolysis and increases glycogen
production in the liver. In summary, HGH spares
proteins and carbohydrates by enhancing the use
of lipids as an energy source for cell functions.
HGH has a half-life of about 20 hours after
secretion, after which it is no longer chemically
active. HGH, acting as a tropic hormone, triggers
the production of growth factorsin the liver and
other tissues. These growth factors (composed of
protein molecules) prolong the effects of HGH on
bone and cartilage tissues.
Levels of HGH tend to decrease with age. The
resulting decline in protein synthesis may be
responsible for some of the characteristic signs
of aging, such as diminished muscle mass
and wrinkles.
Insufficient HGH production during childhood
results in a condition called pituitary dwarfism.
This disorder results in abnormally short stature.
But, unlike genetic dwarfism, body proportions
(the length of arms and legs and the size of the
head) are normal. Puberty may be delayed or not
occur at all. Pituitary dwarfism may be the result of
a pituitary tumour or the total absence of a pituitary
gland. Measurement of growth hormone levels inthe blood is used to confirm the diagnosis of
pituitary dwarfism (see Figure 6.9).
In the past, treatment of pituitary dwarfism
required the extraction of growth hormone from the
pituitary glands of human cadavers. However, this
source yielded insufficient quantities of the
hormone. In addition, growth hormones from
animal sources were not suitable for human use.
However, current biotechnology techniques now
provide a much more reliable supply of this
hormone. These procedures involve inserting
sections of DNA that code for HGH into certain
strains of bacteria. The altered, rapidly reproducing
bacteria are thus transformed into biochemical
factories that produce HGH as a “waste product.”Figure 6.9The amount of human growth hormone
produced during childhood affects the height of an
individual. The symptoms of both inadequate and
excessive growth hormone are readily treated today.An excess of HGH production prior to puberty
causes a disorder known as gigantism(as illustrated
in Figure 6.9). The symptoms of gigantism are
primarily the result of abnormal growth of long
bones in the skeleton. The disorder is easily treated
by the microsurgical removal of a tumour from the
pituitary gland, irradiation of gland tissue, or both.