Pars intermedia, anterior pituitary gland.
Mallory trichrome and H&E,
originates from the ectoderm of the
and is part of the adenohypophysis. This bandlike struc-
ture lies between the
. It is of the
same embryonic origin as the pars distalis. The pars intermedia
contains colloid cysts called
, which are lined by
cuboidal to columnar follicular cells. These cells are associated
with the formation of
in the fetus. This photomicrograph
shows several colloid-F
lled cysts (Rathke cysts). Most cells in
the pars intermedia resemble
blood vessel separates the pars intermedia and the pars distalis.
Blood supply of the pituitary gland.
superior hypophyseal arteries
, which arise from the internal carotid artery and posterior communicating artery of the circle of
Willis, supply the pars tuberalis, the infundibular (neural) stalk, and the median eminence. The
darker shaded area
primary capillary plexus
, which receives blood from the superior hypophyseal arteries, drains blood into the hypophyseal portal
veins supplying the
secondary capillary plexus
white shaded area
), and, F
nally, drains into the hypophyseal veins. Both primary and
secondary capillary plexuses contain fenestrated capillaries. The portal blood circulation (from primary to secondary capillary plex-
uses) carries neurosecretory hormones from the median eminence into the pars distalis where they stimulate or inhibit basophils and
acidophils to produce hormones. The pars nervosa receives blood mainly from the
inferior hypophyseal arteries
, which arise from the
internal carotid artery. This artery also receives blood from the trabecular artery, which arises from the superior hypophyseal artery.
The hormones released by
enter the blood circulation through the capillary plexuses of the inferior hypophyseal
and trabecular arteries.