Growth hormone (GH / somatotropin) acts on most somatic (body) tissues, stimulating growth, cell reproduction, and regeneration. Its primary effects include: stimulating liver to produce IGF-1 (insulin-like growth factor 1), promoting protein synthesis, stimulating bone and cartilage growth, and regulating fat and carbohydrate metabolism. GH acts directly on many tissues and indirectly via IGF-1. It does not primarily target the thyroid, gonads, or interrenal gland.