Posterior pituitary: oxytocin and ADH made in the hypothalamus
The posterior pituitary stores and releases oxytocin (which acts on the breast and uterus) and antidiuretic hormone, ADH (which acts on the kidney); the hypothalamus makes both.
Remember
The posterior pituitary only stores and releases oxytocin and ADH, which the hypothalamus makes, so it is not a true endocrine gland and damage to it impairs release, not synthesis (the making of the hormones).
Memory aid
the posterior pituitary is a post office, not a factory
It stores and releases hormones that the hypothalamus makes, rather than making them itself.
The pituitary gland is made up of the anterior and the posterior pituitary. The anterior pituitary is a true endocrine gland: it makes and releases its own hormones. The posterior pituitary does not make its hormones. The hypothalamus makes them, and the posterior pituitary stores and releases them.
Oxytocin and antidiuretic hormone (ADH) are made by neurosecretory cells (nerve cells that release hormones) in two clusters of nerve cell bodies in the hypothalamus, the supraoptic and paraventricular nuclei. The hormones are carried down the axons (the long nerve fibres) of these cells through the pituitary stalk, which physically connects the hypothalamus to the posterior pituitary, and are stored in the nerve endings there. When the nerve cells are stimulated, the hormones are released into the general circulation and travel to distant targets.
Oxytocin triggers the milk let-down reflex (the squeezing of milk from the breast when a baby suckles) and uterine contractions in labour. ADH promotes water reabsorption in the nephron of the kidney, so the urine becomes more concentrated.
Damage to the posterior pituitary impairs release, not synthesis (the making of the hormones). If the hypothalamus is intact, its nerve cells keep making the hormones. The storage and release site is damaged, however, so secretion into the circulation falls. A fall in ADH causes large volumes of dilute urine and thirst, known as cranial diabetes insipidus.
The two lobes also differ in origin. The anterior pituitary arises from an upgrowth of the primitive mouth (oral ectoderm), and the posterior pituitary from neuroectoderm (primitive brain tissue), which fits its role as an extension of the hypothalamus.
Key facts
- Made in
- the supraoptic and paraventricular nuclei of the hypothalamus, not in the posterior pituitary.
- Route
- down the axons through the pituitary stalk to the posterior pituitary, where the hormones are stored.
- Release
- into the general circulation when the nerve cells are stimulated, to act at distant targets.
- Oxytocin
- triggers milk let-down and uterine contractions.
- ADH
- promotes water reabsorption, so the urine becomes more concentrated.
- Development
- the posterior pituitary arises from neuroectoderm and the anterior pituitary from oral ectoderm.
- If the posterior pituitary is damaged
- with the hypothalamus intact, the hormones are still made, but their release into the blood is reduced.
Exam traps
- Growth hormone and prolactin (which stimulates breast development and milk production) do not come from the posterior pituitary: both are made and released by the anterior pituitary.
- Development from oral ectoderm does not explain why the posterior pituitary is not a true gland: oral ectoderm forms the anterior pituitary, and the posterior pituitary arises from neuroectoderm.
- Oxytocin and ADH do not travel up from the posterior pituitary to the hypothalamus: the hypothalamus makes them, and they pass down the axons to the posterior pituitary.
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