pituitary gland
Meaning of pituitary gland: Called the master gland, it takes its own orders from the hypothalamus directly above, which makes the title only half deserved.
Definition of pituitary gland
The pituitary gland is a pea-sized structure sitting in a bony hollow at the base of the brain, joined to the hypothalamus by a short stalk. It releases hormones that set the output of the thyroid, the adrenal glands and the ovaries or testes, and others acting directly on growth, milk production, water balance and labor.
What does each lobe release?
| Lobe | Hormones | Where they are made |
|---|---|---|
| Anterior | Growth hormone, thyroid-stimulating hormone, adrenocorticotropic hormone, the two hormones driving the ovaries and testes, and prolactin | In the anterior lobe itself |
| Posterior | Antidiuretic hormone, which conserves water, and oxytocin, which acts in labor and breastfeeding | In the hypothalamus, then stored here until released |
Most of these are instructions to another gland rather than end products. Adrenocorticotropic hormone tells the adrenal cortex to make cortisol, thyroid-stimulating hormone tells the thyroid gland to make thyroid hormone, and the level of the end product feeds back to restrain further release. That loop is what makes a pituitary problem hard to read from one result: a low thyroid hormone with a low stimulating hormone points upward to the pituitary, while a low thyroid hormone with a high stimulating hormone points to the thyroid itself.
How does the brain control each lobe?
By two entirely different routes. The anterior lobe is controlled chemically. The hypothalamus releases tiny amounts of releasing and inhibiting factors into a private set of blood vessels running down the stalk, and those vessels carry them straight into the anterior lobe without diluting them in the general circulation. The posterior lobe is controlled electrically, because it is nervous tissue rather than glandular: its hormones travel down the axons of hypothalamic nerve cells and wait in the endings until a nerve impulse discharges them. Prolactin is the odd one out, held down rather than driven, restrained by dopamine arriving along the stalk. Cutting or compressing the stalk therefore lowers most anterior hormones while raising prolactin.
What goes wrong here?
Benign tumors are the common problem. Some flood the body with one hormone, producing effects such as excess cortisol, acromegaly or milk production unrelated to childbirth. Others make nothing and cause trouble by size alone, because the crossing point of the optic nerves lies immediately above the gland and pressure there classically erodes the outer half of the visual field in each eye. Function can also be lost, gradually or, in the case of bleeding into the gland, suddenly.
Used in a sentence
Imaging of the pituitary gland was obtained after laboratory testing suggested a hormonal abnormality.
Good to know
The anterior and posterior lobes differ both in the hormones they release and in how the hypothalamus reaches them, chemically through a private blood supply for the anterior lobe and directly along nerve fibers for the posterior, a distinction relevant when interpreting pituitary hormone abnormalities.
Word origin
Where “pituitary gland” comes from
From Latin pituita, meaning phlegm or mucus, since early anatomists believed the gland secreted mucus into the nose.