Pituitary

The pituitary is also known as hypophysis. It is composed of two embryologically distinct tissue. The anterior pituitary or adenohypophysis is derived from the roof of the' mouth and the posterior pituitary or neurohypophysis is derived from the hypothalamus. Pituitary is joined to the hypothalamus by a slender stalk of nervous tissue. The neurohypophysis consists mostly of neuroscretory nerve endings. The cell bodies of these neurons originate in the hypothalamus (These were the neurons investigated by Scharrer and his associates). Neuroscretory cells differ from conventional neurons in position and structure of nerve endings.

They have more nerve endings so that they secrete greater amounts of neurohormones when stimulated. The size of the neuroscretory granules is also larger (200-500 nm) than those found in other nerve synapses (40-100 nm). These hypothalamic nerve cells synthesise two hormones, vasopressin or antidiuretic hormone (ADH) and oxytocin. These are transported along the, axons, stored and ultimately released from nerve endings, in the posterior pituitary lobe. The anterior pituitary lobe, however, synthesises and releases at least 7 peptide hormones.