Page 28 - Module 1-Anatomy and Physiology of Growth Hormone Function Final (Interactive)

Module 1: Anatomy and Physiology of Growth Hormone

Key Takeaways

• One of the key hormones involved in the growth of the human body, protein
synthesis, metabolism, and cellular replication is growth hormone (GH), also
called somatotropin—a protein hormone produced and secreted by the anterior
pituitary gland.
• Its primary function is anabolic; it promotes protein synthesis and tissue building.
• The two main regulators of release are GH-releasing hormone (GHRH) and
somatostatin, also known as GH-inhibiting hormone (GHIH), which have
stimulatory and inhibitory effects respectively.
• IGF-1 levels increase during puberty, peaks after puberty, and decline during the
later years.
• Abnormal GH synthesis, which typically occurs in GH deficiency or acromegaly,
reduces or increases IGF-1 levels, respectively.
• IGF-1 exerts its physiologic effects by binding to specific cell surface receptors.
• Although IGF-1 binds primarily to the IGF-1 receptor, some effects may be
facilitated through the IGF-2 and insulin receptors.
• Longitudinal bone growth is stimulated by GH directly on the growth plate, locally
produced IGF-1 in response to GH stimulation and circulating IGF-1.
• During the first year of life, longitudinal growth rates are high, followed by a
decade of modest longitudinal growth.
• Longitudinal growth takes place by a process called endochondral ossification, in
which a cartilaginous scaffold is replaced by bone in a coordinated fashion.
• GH acts on resting zone chondrocytes and is responsible for local IGF-1
production, which stimulates clonal expansion of proliferating chondrocytes in an
autocrine/paracrine manner.
• During puberty, there can be a 1.5- to 3-fold increase in the pulsatile secretion of
GH and a more than 3-fold increase in the concentration of serum IGF-1.
• Growth hormone activates the Janus kinase (JAK)–signal transducer and
activator of transcription (STAT) signaling pathway.

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