The @entity4727 ( @entity4727 ) acts on bones, intestines, and kidneys to maintain the @entity460 homeostasis which, in turn, is a main factor in controling the parathyroid (PT) gland activity. In all mammals studied, the chief cells of PT glands changed their size, shape, and cytoplasmic structure due to different functional states which vary the serum @entity460 levels. The chief cells of the @entity35 PT glands were classified as dark and light. The dark cells may constitute an active form, characterized mainly by the abundant free ribosomes, conspicuous rough endoplasmic reticulum, and GOLGI complexes, greater number of secretory granules (SG) and increased tortuosity of the plasma membranes as compared to the light ones which were considered as a less active type of cells. Due to different @entity460 requirements in newborn and young @entity35 for the ossification of growing skeleton and in adult and senile @entity35 with consolidate mature bones, the PT glands studied with electron microscope showed various cytological features. The parenchyma of newborn and young PT glands was composed by dark chief cells. The light chief cells were more frequent in adult and senile animals as a less active type of cell. Mature SG were only occasionally observed in dark cells of newborn, young and adult PT glands. They may constitute a reserve supply of @entity4727 but probably not the main way of secretion, according to their little number. Another pool of @entity4727 probably answers the needs for the small basal variations in the steady-state secretion and may be represented by the vesicles observed in the chief cells cytoplasm.

Light- and electron microscopic observations on parathyroid glands in different age groups of XXXX .

@entity35 :: ('10116', 'Species') :: ['rat', 'rats'] @entity4727 :: ('24694(Tax:10116)', 'Gene') :: ['parathyroid hormone', 'PTH'] @entity460 :: ('MESH:D002118', 'Chemical') :: ['calcium']
@entity35 :: (10116,Species) :: ['rats']
