REACTIVE DEPRESSION
t h e g e n i t a l t r a c t , s u c h a s
c h la m y d ia l in f e c -
tio n ,
o r o f t h e i n t e s t i n a l t r a c t , s u c h a s
g a s t ro e n t e rit is .
I f t h e r e i s a d d i t i o n a l i n -
f l a m m a t i o n e l s e w h e r e i n t h e b o d y , s u c h
a s i n t h e e y e s , t h e c o n d i t i o n i s k n o w n a s
R e ite r’s s y n d ro m e .
re a c tiv e d e p re s s io n
A
t e r m
t h a t
w a s
f o r m e r l y
u s e d
t o
d e s c r i b e a t y p e o f
d e p re s s io n
( f e e l i n g s
o f s a d n e s s , h o p e l e s s n e s s , a n d a l a c k o f
i n t e r e s t i n l i f e ) r e s u l t i n g f r o m
a s t r e s s f u l
o r e m o t i o n a l e v e n t o r p e r i o d o f l i f e . I n
c o n t r a s t ,
a n o t h e r
t y p e
o f
d e p r e s s i o n
k n o w n
a s
“ e n d o g e n o u s
d e p r e s s i o n ”
w a s
s e e n t o
o r i g i n a t e f r o m
b i o l o g i c a l
f a c t o r s
w i t h i n
a n
i n d i v i d u a l .
I n
t h e
m
a j o r i t y o f c a s e s , h o w e v e r ,
d e p r e s s i o n
i s a c o m
b i n a t i o n o f t h e s e t w o t y p e s .
re a c tiv e h y p o g ly c a e m ia
A
f o r m
o f
h y p o g ly c a e m ia
( l o w
b l o o d
g l u c o s e l e v e l s ) t h a t o c c u r s w i t h i n a f e w
h o u r s o f e a t i n g
f o o d s t h a t a r e r i c h i n
g l u c o s e . I n r e a c t i v e h y p o g l y c a e m i a , t h e
b o d y o v e r r e a c t s t o t h e s u d d e n r i s e i n
b l o o d s u g a r b y r e l e a s i n g l a r g e a m o u n t s
o f
in s u lin .
T h i s
r e s u l t s
i n
a
r a p i d a n d
e x c e s s i v e d r o p i n t h e b l o o d s u g a r l e v e l
c a u s i n g h y p o g l y c a e m i c s y m p t o m s .
re a g e n t
A t e r m
t h a t i s
u s e d f o r
a n y
c h e m i c a l
s u b s t a n c e t h a t t a k e s p a r t i n a c h e m i c a l
r e a c t i o n . T h e
t e r m
u s u a l l y
r e f e r s
t o
a
c h e m i c a l o r a m i x t u r e o f c h e m i c a l s t h a t
a r e u s e d i n c h e m
i c a l a n a l y s i s ( s e e
a n a ly -
s is , c h e m ic a l)
o r u s e d t o
d e t e c t a b i o -
l o g i c a l s u b s t a n c e .
re b o x e tin e
A n
a n t id e p re s s a n t d ru g
t h a t
b l o c k s
t h e
r e u p t a k e o f
n o ra d re n a lin e
( n o r e p i n e p h -
r i n e )
w i t h i n t h e n e r v o u s s y s t e m . S i d e
e f f e c t s o f r e b o x e t i n e i n c l u d e i n s o m n i a ,
s w e a t i n g , a n d d i z z i n e s s o n s t a n d i n g .
re c e d in g c h in
U n d e r d e v e l o p m e n t
o f t h e
l o w e r
j a w .
T h e c o n d i t i o n c a n b e c o r r e c t e d b y t h e
u s e
o f
o r t h o d o n t ic a p p lia n c e s
i f u s e d i n
t h e g r o w t h s p u r t a t a d o l e s c e n c e o r b y
c o s m e t ic s u rg e ry .
re c e d in g g u m s
W
i t h d r a w a l o f t h e g u m s f r o m
a r o u n d
t h e t e e t h , r e s u l t i n g i n t h e e x p o s u r e o f
p a r t o f t h e r o o t s . T h e t e e t h m a y b e c o m e
s e n s i t i v e t o h o t a n d c o l d s u b s t a n c e s a n d
R
TYPES OF RECEPTOR
Stimuli are detected by the free endings ofsensory nerve cells or by special structures
forming the endings ofthese cells. These respond to specific stimuli (such as light of
a certain wavelength) and send a signal indicating the presence ofthe stimulus to
the spinal cord and/or the brain. Cell surface or chemical receptors (right) are tiny
structures on the outer surface ofa cell. They allow certain chemicals to bind to the
cell and trigger some change within it.
Skin receptors
The skin contains many
types ofreceptor that
respond to stimuli such as
pressure, cold, heat, and
hair movement, allowing
the sensations of touch,
temperature, and pain.
They include such
structures as pacinian
corpuscles and Merkel’s
discs and are all special
types of nerve cell ending.
Hairshaft
M erkel’s disc
M eissner’s
corpuscle
Pacinian
corpuscle
Organ o f Ruffini
Subcutaneousfat
Receptors in tongue
Each taste-bud (below)
consists of many receptor
cells. Each has surface
receptors that respond
to chemicals in food.
Receptors in eye
The retina, located at the
back ofthe eye, contains
receptor cells, called rods
and cones, which are
responsive to light.
Supporting
Taste
Taste
Tongue
Vitreous hum our
Nerve fibres
Ganglion cell
Bipolarcell
Cone
Rod
HOW CELL SURFACE OR
CHEMICAL RECEPTORS WORK
Most cells have many surface
receptors (only one is shown
below). Their existence allows the
activity ofthe cell to be influenced
from outside.
Nucleus
Other
chemicals
Receptor
area
Other
chem icals
- Hormone
molecule
1
A receptor allows only one specific
chemical (which may be a hormone
or a neurotransmitter substance) to
bind to it. The chemical must have a
configuration that “fits” the receptor.
2
The binding of chemical to receptor
alters the outer cell membrane and
triggers a change, such as contraction by
a muscle cell or increased activity in an
enzyme-producing cell.
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