Physiologically, the pituitary is divided into two distinct lobes that arise from different embryological sources. The anterior lobe, or adenohypophysis, grows upward from the pharyngeal tissue at the roof of the mouth. An intermediate lobe also originates in the pharynx, but in humans it is greatly reduced in structure and function. The posterior lobe, or neurohypophysis, grows downward from neural tissue. It is structurally continuous with the hypothalamus of the brain, to which it remains attached by the hypophyseal, or pituitary, stalk. The hypothalamus controls almost all secretions of the pituitary. The posterior lobe is controlled by nerve fibers that originate in hypothalamic neurons and the anterior lobe by substances that are transported from the hypothalamus by tiny blood vessels.
The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.