Pars intermedia

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Pars intermedia
Median sagittal through the hypophysis of an adult monkey. (Pars intermedia labeled at bottom center.)
Latin pars intermedia adenohypophyseos
TA A11.1.00.004
TH H3.
FMA 74632
Anatomical terminology
Pars intermedia is seen between pars distalis and pars nervosa.

Pars intermedia is the boundary between the anterior and posterior lobes of the pituitary. It contains three types of cells - basophils, chromophobes, and colloid-filled cysts. The cysts are the remainder of Rathke’s pouch.

In human fetal life, this area produces melanocyte stimulating hormone or MSH which causes the release of melanin pigment in skin melanocytes (pigment cells). However, the pars intermedia is normally either very small or entirely absent in adulthood.

In lower vertebrates (fish, amphibians) MSH from the pars intermedia is responsible for darkening of the skin, often in response to changes in background color. This color change is due to MSH stimulating the dispersion of melanin pigment in dermal (skin) melanophore cells.

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