CHAPTER 17
Endocrine System
331
Blood vessel
Blood vessel
Blood vessel
Colloid
Colloid
Colloid
Rathke
Rathke
cysts
cysts
Rathke
cysts
Follicular cells
Follicular cells
Follicular cells
Pars
Pars
distalis
distalis
Pars
distalis
Blood cells
Blood cells
Blood cells
Pars
Pars
nervosa
nervosa
Pars
nervosa
A
Figure 17-5A.
Pars intermedia, anterior pituitary gland.
Mallory trichrome and H&E,
3
127
The
pars intermedia
originates from the ectoderm of the
Rathke
pouch
and is part of the adenohypophysis. This bandlike struc-
ture lies between the
pars distalis
and
pars nervosa
. It is of the
same embryonic origin as the pars distalis. The pars intermedia
contains colloid cysts called
Rathke cysts
, which are lined by
cuboidal to columnar follicular cells. These cells are associated
with the formation of
MSH
in the fetus. This photomicrograph
shows several colloid-F
lled cysts (Rathke cysts). Most cells in
the pars intermedia resemble
basophilic cells
(
melanotrophs
). A
blood vessel separates the pars intermedia and the pars distalis.
Branch of
internal
carotid artery
Hypophyseal
vein
Trabecular
artery
Superior
hypophyseal
arteries
Inferior hypophyseal
artery
Median
eminence
Hypothalamus
Secondary
capillary
plexus
Primary
capillary
plexus
Hypophyseal
veins
Median
eminence
Hypophyseal
portal veins
Anterior lobe
Posterior lobe
B
Figure 17-5B.
Blood supply of the pituitary gland.
The
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
indicates the
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
Herring bodies
enter the blood circulation through the capillary plexuses of the inferior hypophyseal
and trabecular arteries.
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