VAN 211: Veterinary Histology and Embryology (2+2)

PITUITARY GLAND

• The hypophysis cerbri or pituitary gland is an ectodermal derivative and an endocrine gland of double orgin. One part glandular in nature is derived from the epithelium of the stomodeum while the other not so plainly secretory is a specialized extension from the brain.
• A dorsal evagination the Rathke’s pouch from the roof of the buccal cavity just in front of the oral membrane forms the epithelial part of the gland. The pouch elongates and the stalk degenerates. The pouch enlarges and embraces the infundibulum, an invagination from the floor of the forebrain vesicle. The infundibulum forms the non-epithelial part of the gland.
• At about four months, the cranial wall of the pouch thickens greatly and differentiates into pars anterior and the caudal wall remains thin and forms pars intermedia. Very early in development, a pair of buds detaches from the pouch and encircles the infundibulum and forms pars tuberalis.
• The original lumen of the Rathke’s pouch becomes reduced t the oblique cleft between the pars anterior and pars intermedia in the adult and is filled with a glairy fluid. The tubular primordium of the neural lobe is transformed into a solid structure composed of nerve fibres neuroglial tissue and certain spindle shaped cells and this forms the pars nervosa of the gland.