Page 17 - Module 1-Anatomy and Physiology of Growth Hormone Function Final (Interactive)

Module 1: Anatomy and Physiology of Growth Hormone

Deficiencies of leptin or its receptor can be responsible for a variety of hypothalamic
abnormalities, including hyperphagia, obesity, and central hypogonadism which can
cause growth disorders.

Insulin-like Growth Factor-1

IGF-1 was introduced in Part 1 of this module. It was previously stated that most
tissues produce IGF-1 as a result of GH stimulation and that the liver is the major
source of circulating IGF-1. Serum IGF-1 concentrations are influenced by factors
such as age, gender, pituitary function, and nutritional status. For example:

• IGF-1 levels increase during puberty, peak after puberty, and decline with
increasing age. After reaching adulthood, secretion of GH and IGF-1 declines
continuously to very low levels in those aged ≥60 years.

• Abnormal GH synthesis, which typically occurs in GH deficiency and acromegaly,
reduces or increases IGF-1 levels, respectively.

• Poor nutrition and decreased caloric intake are associated with GH resistance,
resulting in low IGF-1.

Approximately 75% of circulating IGF-1 is synthesized in the liver and is used
remotely to carry out endocrine-related functions. In contrast, approximately 25% of
IGF-1 is synthesized in bones, cartilage, the central nervous system, kidneys,
ovaries, and red blood cell precursors that carry out other types of functions.

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