Vihypophysis Figure 12

A. Adenohypophysis 1. Formation

Infundibulum

Pars tuberalis of anterior lobe of hypophysis

Rathke Pouch Embryo

pouch

Oral cavity

Pharyngeal hypophy3i3

Pars tuberalis of anterior lobe of hypophysis

Rathke Pouch Embryo
Posterior lobe of hypophysis (neurohypophysis)

pouch

Oral cavity

Pharyngeal hypophy3i3

Anterior lobe of hypophysis

(adenohypophysis)

Pars intermedia of anterior lobe of hypophysis

Figure 12-4. Schematic drawings illustrating the development of the hypophysis (pituitary gland). (A) A mid-sagittal section through the 6-week-old embryo, showing Rathke's pouch as a dorsal outpocketing of the oral cavity and the infundibulum as a thickening in the floor of the hypothalamus. (B, C) Development at 11 weeks and 16 weeks, respectively. The anterior lobe, the pars tuberalis, and the pars intermedia are derived from Rathke's pouch. (Modified from Sadler TW: Langman's Medical Embryology, 6th ed. Baltimore, Williams & Wilkins, 1990, p .373.)

a. The adenohypophysis develops from an evagination of ectoderm lining the roof of the primitive mouth called Rathke's pouch.

b. Rpx, Lhx-3, and Lhx-4 (homeobox genes) appear to play a role in the formation of Rathke's pouch.

2. Clinical correlations a. Craniopharyngioma is a congenital cystic tumor resulting from remnants of Rathke's pouch.

b. Pituitary dwarfism. A well-characterized subset of individuals with pituitary dwarfism is deficient not only in growth hormone (GH) but also in thyroid-stimulating hormone (TSH) and prolactin (PRL). The combined deficiency of GH, TSH, and PRL is caused by a genetic mutation in the Pit-1 gene, which encodes for a transcription factor called Pit-1. Pit-1 transcription factor is required for the normal transcription of GH, TSH, and PRL.

B. Neurohypophysis. The neurohypophysis develops from an evagination of neuroectoderm from the diencephalon (i.e., specifically from the hypothalamus).

1. Preganglionic sympathetic neurons within the intermcdiolaceral cell column originate from the basal plate of the neural tube (i.e., neuroectoderm).

2. Postganglionic sympathetic neurons within the sympathetic chair, ganglia and prevertebral ganglia (e.g., celiac ganglion) originate from neural crest cells.

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