Page 8 - Module 1-Anatomy and Physiology of Growth Hormone Function Final (Interactive)

Module 1: Anatomy and Physiology of Growth Hormone

Pituitary Gland

As mentioned previously, the pituitary gland is located within the sella turcica, in front
of the brain stem, and just below the thalamus. It consists of anterior and posterior
lobes (Figure 3).

Figure 3. Pituitary gland

The pituitary gland controls the function of most endocrine glands and receives
feedback from a variety of systems in order to maintain homeostasis.

By detecting the levels of hormones produced by glands under the
pituitary's control (target glands), the hypothalamus or the pituitary can
determine how much stimulation the target glands need.

Most of the hormones produced by the pituitary gland (Figure 4) are released in
bursts; every 1 to 3 hours. This is called pulsatility which describes the alternating
periods of activity and inactivity. Studies have shown that for GH, plasma insulin-like
growth factor-1 (IGF-1) concentrations correlate more with mean 24-hour GH
concentrations — basal GH levels — and not GH pulses.

• Some hormones follow what is called a diurnal rhythm, which means that the
levels rise and fall during the day at somewhat predictable times. Many hormones
peak just before waking and have the lowest values prior to the onset of sleep.
This is common for GH and makes sense from an evolutionary standpoint, as
humans need to access energy stores, which is liberated from fat depots during
the night while fasting. At the time of peaks, GH is forced into the tissues.

• The levels of other hormones vary based on factors that are specific to a body
function or target organs.

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