Pituitary gland hypophysis

The pituitary gland and the hypothalamus, the portion of the brain to which the pituitary gland is attached, are morphologically and functionally linked in the endocrine and neuroendocrine control of other endocrine glands. Because they play central roles in a number of regulatory feedback systems, they are often called the "master organs" of the endocrine system.

Gross Structure and Development

The pituitary gland is composed of glandular epithelial tissue and neural (secretory) tissue

The pituitary gland is a pea-sized, compound endocrine gland that weighs 0.5 g in males and 1.5 g in multiparous females. It is centrally located at the base of the brain, where it lies in a saddle-shaped depression of the sphenoid bone called the sella turcica. A short stalk, the infundibu-lum, and a vascular network connect the pituitary gland to the hypothalamus.

The pituitary gland has two functional components (Fig. 20.2):

• Anterior lobe (adenohypophysis), the glandular epithelial tissue

• Posterior lobe (neurohypophysis), the neural secretory tissue

These two portions are of different embryologic origin. The anterior lobe of the pituitary gland is derived from an evagination of the ectoderm of the oropharynx toward the brain (Rathke's pouch). The posterior lobe of the pituitary gland is derived from a downgrowth (the future infundibulum) of neuroectoderm of the floor of the third ventricle (the diencephalon) of the developing brain (Fig. 20.3).

The anterior lobe of the pituitary gland consists of three derivatives of Rathke's pouch:

• Pars distalis, which comprises the bulk of the anterior lobe of the pituitary gland and arises from the thickened anterior wall of the pouch

• Pars intermedia, a thin remnant of the posterior wall of the pouch that abuts the pars distalis

• Pars tuberalis, which develops from the thickened lateral walls of the pouch and forms a collar or sheath around the infundibulum

The embryonic infundibulum gives rise to the posterior lobe of the pituitary gland. The posterior lobe of the pituitary gland consists of

• Pars nervosa, which contains neurosecretory axons and their endings

• Infundibulum, which is continuous with the median eminence and contains the neurosecretory axons forming the hypothalamohypophyseal tracts.

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