Pituitary gland

The pituitary gland hangs from the underside of the hypothalamus on a short stalk, the infundibulum, and sits in a saddle-shaped hollow of the sphenoid bone called the sella turcica, just above the back of the nose and below the optic chiasm, where the optic nerves cross. It is about a centimeter across and has two lobes with different origins: the anterior pituitary (adenohypophysis) grows up from tissue of the embryo's mouth, while the posterior pituitary (neurohypophysis) grows down from the brain.

The anterior lobe makes its own hormones under the control of releasing and inhibiting hormones that reach it from the hypothalamus through a small portal system of blood vessels. Its six main products are growth hormone, prolactin, thyroid-stimulating hormone, adrenocorticotropic hormone (ACTH), follicle-stimulating hormone and luteinizing hormone; four of these direct other endocrine glands, which is why the pituitary is often called the master gland. The posterior lobe makes no hormones itself. It stores and releases antidiuretic hormone and oxytocin, produced by hypothalamic neurons whose axons end there. Negative feedback from target-gland hormones keeps output in check.

Pituitary adenomas, usually benign tumors, can overproduce a hormone, as in acromegaly from excess growth hormone, or press on the optic chiasm and narrow the field of vision.