21.8: The Pituitary Gland
The pituitary is a small endocrine organ in the sphenoid bone under the hypothalamus. Primarily, the pituitary in adults has two distinct anatomical and functional regions— the anterior and posterior lobes. During human fetal development, a third pituitary gland region called the pars intermedia atrophies and disappears. However, some of its cells migrate and exist adjacent to the anterior pituitary in adults.
- The anterior lobe comprises the pars distalis and the pars tuberalis. These areas consist of glandular epithelial tissue that produces various hormones. The anterior lobe is linked to the hypothalamus through the hypophyseal portal system. The hormones secreted by the ventral hypothalamus cells travel through this portal system and regulate hormone-secreting cells of the anterior lobe.
The posterior pituitary lobe has two parts: the infundibulum, a funnel-shaped stalk, and the pars nervosa. The infundibulum allows the passage of the supra-optic and paraventricular nuclei axons of the hypothalamic-hypophyseal tract, maintaining a neural connection with the hypothalamus. The hypothalamic-hypophyseal tract delivers hormones secreted by hypothalamic neurosecretory cells into the posterior pituitary lobe for storage and release.
