Wingfield 1

Sagikalimagethroughpituitaryglandshowsdiuseenlargement

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Unformatted text preview: V1

 
 
phospholipaseC
 





 
cyclase
acBvaBon:
cAMP

 
 
acBvaBon:
Ca2+,






 

producBon
&
protein

 
 
inositol
triphosphate








kinase
A
sBmulaBon
 
 
&
diacyl
glycerol
 
 
mobilizaBon
 

 V2 receptor action Aquaporin Side view of AQP showing the pore profile (turquoise dots) and the residues that line the pore (opaque ball-and-stick structures). The extracellular vestibule is above; cytoplasmic, below. The pinched-in area with the highest concentration of turquoise dots is the constriction region. More than ten different aquaporins have been found in human body. They form tetramers in the cell membrane, and facilitate the transport of water and, in some cases, other small solutes across the membrane. 
 However, the water pores are completely impermeable to charged ions such as protons.
 A remarkable property that is critical for the conservation of membrane's electrochemical potential, but paradoxical at the same time, since protons can usually be transferred readily through water molecules. 
 Water molecules passing the channel are forced, by the protein's electrostatic forces, to flip at the center of the channel, thereby breaking the alternative donor-acceptor arrangement that is necessary for proton translocation. Aquaporin-2 in the absence of vasopressin, resides in membrane vesicles in the cytoplasm. Binding of vasopressin to its V2 receptor stimulates transcription of the aquaporin-2 gene, and insertion of the intracellular pool of aquaporin-2 into the apical membrane. The cell is now able to efficiently take up water from the lumen of the duct. Aquaporin-3 is constitutively expressed in the basolateral membrane. When water floods into the cell through aquaporin-2 channels, it can rapidly exit the cell through the aquaporin-3 channels and flow into blood. SagiKal
image
through
pituitary
gland
shows
diffuse
enlargement
of

 
gland
and
pituitary
stalk.
Blockage
of
AVP
release.
This
can
lead
 
to
diabetes
insipidus.
 www.ajronline.org/cgi/content‐nw/full/182/6/1560/FIG1
 Mechanisms
that
underlie
the
pathophysiology
of
the
triphasic
 paKern
of
postoperaBve
diabetes
insipidus
 The
first
phase
of
diabetes
insipidus

 is
ini=ated
by
a
par=al
or
complete

 pituitary
stalk
sec=on,
which
severs

 the
connec=ons
between
the
cell

 bodies
of
AVP‐secre=ng
neurons
in

 the
hypothalamus
and
their
nerve
 terminals
in
the
posterior
pituitary

 gland,
which
prevents
AVP
secre=on.
 This
fir...
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