Many glands which produce hormones are influenced by other hormones, particularly those secreted by the hypothalamus (a controlling centre in the brain) and the pituitary gland. If the amount of hormone produced by a gland rises, negative feedback mechanisms operate by instructing the pituitary gland, via the hypothalamus, to produce less of the stimulating hormones. This reduces activity in the target gland. Should the amount of hormone produced fall, the feedback mechanism weakens, with a resulting increase in the output of the stimulating hormones.