- The hypothalamus is an anatomical sub-division of the brain composed of neuronal tissue which lies immediately beneath the thalamus. The hypothalamus is anatomically connected to the pituitary gland by the thin hypophysial stalk which is composed of neuronal and vascular tissue. The neuronal tissue of the hypophysial stalk expands into the posterior pituitary, described below, whereas the vascular component ramifies into the anterior pituitary. The vascular tissue of the hypophysial stalk represents portal vessels which collect blood from capillaries within the hypothalamus and deliver blood to capillaries within the anterior pituitary. These Hypothalamic-Pituitary Portal Vessels allows endocrine hormones released by the hypothalamus to immediately reach the anterior pituitary without being diluted in the general circulation.
- The pituitary gland, also known as the Hypophysis, is a pea-sized structure that sits in the sella turcica and is connected to the hypothalamus by the hypophysial stalk described above. The pituitary is in reality composed of two distinct functional tissues which have different embryological origins. The anterior pituitary, also known as the adenohypophysis, is derived from the pharyngeal epithelium known as Rathke's Pouch whereas the the posterior pituitary, also known as the Neurohypophysis, represents a neural outgrowth of the hypothalamus and so is embryologically related to the brain.