Johnny, a five-year-old boy has been growing by leaps and bounds; his height is 100% above normal for his age. He has been complaining of headaches...

Johnny, a five-year-old boy has been growing by leaps and bounds; his height is 100% above normal for his age. He has been complaining of headaches and vision problems. A CT scan reveals a large pituitary tumor. What hormone is being secreted in excess? What condition will Johnny exhibit if corrective measures are not taken; how would this affect his physical appearance? What is the probably cause of his headaches and visual problems?