Final answer:
Gigantism is caused by the hypersecretion of growth hormone (GH) from the anterior pituitary, and the growth is mediated by somatomedins or insulin-like growth factors (IGFs) released in response to GH.
Step-by-step explanation:
The changes in gigantism, which is the result of hypersecretion of growth hormone (GH) from the anterior pituitary gland (AP), are mediated by the release of somatomedins or insulin-like growth factors (IGFs). These growth factors are produced by the liver and other tissues in response to GH and are the actual agents that lead to the increased growth of bones and tissues seen in gigantism. If this hypersecretion occurs in childhood or adolescence before the growth plates have closed, it can result in abnormally high linear growth and increased height.