The pituitary gland is a very small gland that sits at the base of the skull. Despite its size, it is probably by far the most important gland in the body as it is responsible for regulating most of the other glands in the body, as well as several regular body functions. Most important is its role in producing human growth hormone, which is the key hormone in growth to adulthood.
In addition, the pituitary regulates a hormone that controls urination - without it, the kidneys produce urine continuously, leading to the condition diabetes insipidus.
Several patients on House have had difficulties with their pituitary gland:
In Merry Little Christmas, the patient was suffering from a cancer that prevented the gland from producing human growth hormone - hypopituitary disease. She was mistaken for having dwarfism because her mother was a dwarf.