pituitary gland

The pituitary gland is often called the body's “master gland” because it sends out hormones that direct several other glands. Picture a relay station: it receives orders from the hypothalamus above it and then broadcasts hormonal commands to the thyroid, adrenal glands, gonads, and more.

Despite its importance, the pituitary is tiny — about the size of a pea — and sits in a bony pocket called the sella turcica at the base of the skull, just behind the bridge of the nose. It has two functionally distinct parts that develop from different tissues: the anterior pituitary (an outgrowth of the mouth's roof, made of glandular cells) and the posterior pituitary (an extension of the brain, made of nerve endings).

The anterior pituitary manufactures and secretes its own hormones — growth hormone, prolactin, TSH, ACTH, LH, and FSH — under the chemical control of releasing and inhibiting factors sent from the hypothalamus through a portal blood system. The posterior pituitary does not make hormones; it simply stores and releases oxytocin and vasopressin that were produced by hypothalamic neurons.

Although it is called the master gland, the pituitary is itself a servant: the hypothalamus sits above it in the chain of command, and target glands feed back to restrain pituitary output. So it is better thought of as a crucial middle manager in the endocrine hierarchy.