Introduction to the hypothalamus and pituitary

The hypothalamus and pituitary

Introduction to the hypothalamus and pituitary

The pituitary gland lies in the sella turcica, which is a tightly enclosed bony space at the base of the cranium, roofed by a reflection of the dura. The optic chiasm lies just above the pituitary fossa and the cavernous sinuses run lateral to it. These structures may be affected by expansion of the pituitary gland. It consists of two lobes:

·        The posterior lobe is a physical and functional extension of the ventral hypothalamus. The nerve endings within the posterior pituitary contain and secrete oxytocin and vasopression (antidiuretic hormone).

·        The anterior lobe originates from Rathke’s pouch. Although the anterior lobe is of separate origin to the hypothalamus, it is under its close control. Hypothalamic hormones reach the anterior pituitary in high concentrations via hypophyseal–pituitary portal veins.

The hypothalamus lies just above the pituitary, and has centres for appetite (the satiety centre), thirst, tem-perature control and the sleep–wake cycle. The hypothalamus secretes polypeptide hormones that regulate anterior pituitary hormone secretion, mostly by stimulation. They are secreted episodically and some, e.g. corticotrophin-releasing hormone and thyrotrophin– releasing hormone have an important circadian (circa-about, dia - day) rhythm.

The hypothalamus and pituitary form the basis of the central control of various endocrine axes, which are vital to everyday function (see Fig. 11.2). Disorders of the hypothalamus itself are very rare; however, disorders of the pituitary are common.