Growth hormone. Computer graphic of a molecule of the protein somatotropin, the human growth hormone. It is produced by the anterior lobe of the pituitary gland. Somatotropin causes growth in all or most parts of the body by affecting many metabolic functions, especially the production of proteins. It is a large molecule, being formed of 191 amino acids and having a molecular weight of 22,005. Its production is regulated by the brain's hypothalamus. Over-production causes gigantism and acromegaly, whilst a deficiency leads to dwarfism.