The pituitary gland is a pea-sized bit of tissue at the bottom of your brain. Glands are organs that make and release hormones into your blood. Hormones are chemicals that stimulate other cells or tissues into action. The pituitary gland puts out many different hormones. Each pituitary hormone controls a different gland and body function.
Enlargement of the pituitary gland is when a normal pituitary gland becomes bigger in size for some reason. The change in size can cause your pituitary gland to make too much or too little of certain hormones.
A large pituitary may also push on the nerves that connect your eyes to your brain and cause vision problems.