The pituitary gland is a pea-sized endocrine gland composed of two structurally and functionally separate parts known as anterior and posterior lobes. The pituitary gland's anterior lobe secretes six hormones essential to growth, reproduction, and other basic physiological functions. Abnormal development of the pituitary gland, or hypopituitarism, can cause mild or complete deficiency of one or more pituitary hormones, which manifests as highly varying symptoms. Tumors mainly cause hypopituitarism in humans, but a congenital factor can also be associated with the disorder.