Page 19 - Module 1-Anatomy and Physiology of Growth Hormone Function Final (Interactive)

Module 1: Anatomy and Physiology of Growth Hormone

The importance of this hormone in linear growth is clearly demonstrated by the
severe growth failure in children with congenital IGF-1 deficiency.

IGFs stimulate DNA, RNA, and protein synthesis both in utero and
after birth. After birth, however, IGF-1 appears to have the
predominant role in regulating growth, as where concentrations are
low at birth, increase during childhood and puberty, and begin to
decline after the age of 20.

Influences on GH Levels

In addition to growth-hormone releasing hormone and somatostatin, there are
several other factors that can affect the secretion of growth hormone and therefore
the levels of GH in the blood.

GH secretagogues

Non-GHRH factors release GH through a separate receptor from that of GHRH. One
example mentioned in Part 1, ghrelin, is a circulating peptide made by endocrine
cells in the stomach.

Neural Factors
Neural factors may play a role in GH release, primarily as bursts during sleep. These
are greater in children and tend to decrease with age. Factors that increase stress,
such as surgery, trauma, and exercise, can affect the release of GH.
Metabolic factors

In addition to non-GHRH and neural factors that can influence GH levels, diet has an
influence, specifically through the levels of carbohydrates, proteins, and fat.
• Glucose administration lowers GH in normal, healthy individuals, whereas
hypoglycemia stimulates GH release.
• A protein meal promotes the release of GH. However, states of protein-calorie
malnutrition also increase GH, although the mechanism is not completely clear.
• Fatty acids suppress GH responses to certain stimuli, including arginine and
hypoglycemia. Fasting also stimulates GH secretion, possibly as a means of
mobilizing fat as an energy source.
Effects of other hormones

Other hormones may affect GH levels in the body as well. In situations where there
are an excessive amount of cortisol in the blood, as well as, in hypothyroidism and
hyperthyroidism, GH release may be compromised. Additionally, estrogen can
enhance GH secretion in response to stimulation.

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