= Growth hormone
<Growth hormone> is a <protein> <hormone> synthesized and released by the <anterior pituitary>. It regulates body growth and <metabolism>, acting on tissues directly and partly through <insulin-like growth factor 1> produced by the <liver> and other tissues. Its release is controlled by signals from the <hypothalamus>, including inhibition by <somatostatin>.<Anatomy and Physiology 2e by J. Gordon Betts and others>[§17.3, Growth Hormone and Figure 17.10]{ref}
This makes “growth” a coordinated physiological response rather than merely a change in one chemical concentration. <Growth hormone> can initiate signaling in one tissue, while a second circulating signal influences other tissues. <Negative feedback> connects the resulting signal levels back to their control pathway.<Anatomy and Physiology 2e by J. Gordon Betts and others>[§17.3, hormonal regulation of growth]{ref}
A revealing molecular experiment determined the structure of human <growth hormone> bound to the extracellular portions of the <growth hormone receptor>. The 2.8-angstrom <X-ray crystallography> structure contained one hormone molecule and two receptor portions. Two different surfaces of the hormone contacted the receptor partners. This provides a concrete example of a signaling molecule organizing a multi-part complex, rather than simply occupying one isolated pocket. The structure supported a model for receptor association; establishing the full sequence of activation in a living <biological cell> requires additional functional experiments.<Human growth hormone and extracellular domain of its receptor: crystal structure of the complex by A. M. de Vos and others>[abstract, complex composition, interfaces and proposed dimerization mechanism]{ref}
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