Light micrograph of the pituitary gland showing cells of the anterior lobe. This is a hormone-secreting gland at the base of the brain. It is composed of two lobes, the anterior pituitary and the posterior pituitary. Between the two is the pars intermedia. The anterior pituitary, under the influence of the hypothalamus, secretes hormones that regulate physiological processes including growth, reproduction and stress. The majority of the posterior pituitary consists of the pars nervosa, which contains nerve fibers that secrete hormones synthesized by the hypothalamus into the blood stream.