Pars intermedia

From Biology-Online Dictionary | Biology-Online Dictionary

Definition

noun

The intermediate portion of the pituitary gland, and responsible for the secretion of the melanocyte-stimulating hormone (MSH)


Supplement

The pituitary gland is an endocrine gland situated off the bottom of the hypothalamus. It acts as the master gland of the endocrine system because it is responsible for the release of different hormones that regulate many physiological processes. It consists of three lobes: (1) anterior, (2) intermediate, and (3) posterior.

The intermediate lobe of the pituitary gland is referred to as the pars intermedia. It forms a boundary between the anterior and the posterior lobes of the pituitary gland. Some references include it as part of either the anterior or the posterior lobes. In humans, the pars intermedia is indistinct because it is relatively very small or absent at adulthood. During fetal stage or when present, it secretes melanocyte-stimulating hormone (MSH). In other vertebrates, such as fish and amphibians, its secretion is responsible for the skin darkening. MSH stimulates the distribution of melanin inside the melanophore cells of the skin. Apart from the intermediate lobe, MSH is also produced and secreted in the anterior pituitary, particularly by the corticotrophs. Nevertheless, MSH secreted by the pars intermedia may be called intermedins.

The intermediate part of the pituitary contains three types of cells: the basophils, the chromophobes, and the colloid-filled cysts.


Synonym(s):

  • intermediate part (of pituitary)

See also: