Hypothalamo-Hypophyseal System
The pituitary gland (also called the hypophysis) sends signals to other glands in the endocrine system. It produces many hormones, many of which stimulate the production of other hormones from other endocrine glands. The pituitary gland is controlled by the hypothalamus, which sits directly above it. The pituitary gland is divided into anterior and posterior lobes. The anterior pituitary is the primary hormone-producing aspect, and is under neuroendocrine control, while the posterior pituitary produces only oxytocin and vasopressin (ADH) and is under direct neural control.
Posterior Pituitary
The connection between the hypothalamus and the posterior pituitary is neuronal. The posterior pituitary is a collection of nerve axons whose cell bodies are located in the hypothalamus. Thus, the hormones secreted by the posterior lobe (ADH and oxytocin) are actually neuropeptides; in other words, they are peptides released from neurons.
- The cell bodies of ADH- and oxytocin-secreting neurons are located in supraoptic and paraventricular nuclei within the hypothalamus.
- Although both hormones are synthesized in both nuclei, ADH is primarily associated with supraoptic nuclei and oxytocin is primarily associated with paraventricular nuclei.
- The pituitary gland forms through the invagination of stomodeal ectoderm from the buccal cavity between the 3rd and 15th weeks of development. Positioned directly beneath the hypothalamus, the pituitary is divided into two parts: the anterior and the posterior.
- The anterior pituitary is the main hormone-producing section, regulated by neuroendocrine signals. In contrast, the posterior pituitary is controlled directly by neural input and releases only two hormones: oxytocin and vasopressin (ADH).