KIDNEY IMAGING
THE FUNCTION OF THE KIDNEYS
The kidneys’ main function is
to filter the blood. This activity
is essential in regulating the
body’s fluid balance and acid-
base balance. Each kidney
has about 1 million nephrons,
where the filtering takes place.
A nephron consists of a knot
of capillaries, which is called
a glomerulus, and a tubule,
where urine is formed. Urine
drains out of the kidney via
the ureter; the normal daily
output is 1 to 2 litres.
F i b r o u s c a p s u l e
C o r t e x
RENAL FUNCTION AND AGE
The efficiency of the kidneys diminishes
with age as the number of functional
nephrons is reduced.
1,000,000 -
750,000
500,000
250,000
Nephrons
per kidney
Age
1
1
1
1
1
1
1
1
1
10 20 30 40 50 60 70 80 90
N e p h r o n
M e d u ll a
R e n a l a r t e r y
R e n a l v e in
R e n a l p e l v i s
C a ly c e s
U r e t e r
U r in e f r o m t h e
u r in e - c o ll e c t in g
d u c t s p a s s e s in t o
t h e c a l y c e s o f t h e
k i d n e y , t h e n t o
t h e r e n a l p e l v i s .
It d r a i n s f r o m t h e
k i d n e y v ia t h e
u r e t e r .
A r t e r i o l e s
A r t e r i o l e s a r e t i n y b l o o d v e s s e l s
t h a t c a r r y b l o o d t o a n d fr o m
e a c h g l o m e r u l u s a n d s u r r o u n d
e a c h t u b u l e .
T u b u le
A b o u t 1 4 0 l it r e s o f f i l t e r e d
s a l t a n d w a t e r s o l u t i o n p a s s
f r o m t h e g l o m e r u l i in t o t h e
t u b u l e s e a c h d a y ; 9 9 p e r
c e n t o f i t i s r e a b s o r b e d in t o
t h e s u r r o u n d i n g c a p i l l a r i e s .
T h e c a p i l l a r i e s a l s o r e c la im
o t h e r e s s e n t i a l s u b s t a n c e s ,
s u c h a s a m i n o a c i d s ,
g l u c o s e , b i c a r b o n a t e ,
c a l c i u m , a n d p h o s p h o r u s
a n d , w h e n n e c e s s a r y , a d d
p o t a s s i u m a n d h y d r o g e n
i o n s t o t h e t u b u l a r f l u i d .
G l o m e r u l u s
E a c h g l o m e r u l u s a c t s a s a fil t e r ,
a llo w in g c e r t a i n d i s s o l v e d s u b s t a n c e s
t o p a s s f r o m t h e b l o o d s t r e a m in t o t h e
t u b u l e , b u t p r e v e n t i n g c e l l s a n d l a r g e
p r o t e i n s f r o m c r o s s i n g o v e r .
p o l y c y s t i c
),
d i a b e t e s m e l l i t u s
,
a n d
h y p e r -
t e n s i o n
( h i g h b l o o d p r e s s u r e ) , o r f r o m
l o n g s t a n d i n g o b s t r u c t i o n t o u r i n e f l o w .
SYMPTOMS
T h e m o s t o b v i o u s s y m p t o m o f a c u t e k i d -
n e y f a i l u r e i s o l i g u r i a ( a r e d u c e d v o l u m e
o f u r i n e ) . U r e a a n d o t h e r w a s t e p r o d u c t s
b u i l d u p i n t h e b l o o d a n d t i s s u e s c a u s i n g
d r o w s i n e s s , n a u s e a , a n d b r e a t h l e s s n e s s .
S y m p t o m s o f c h r o n i c k i d n e y f a i l u r e d e -
v e l o p m o r e g r a d u a l l y , a n d m a y i n c l u d e
n a u s e a ,
l o s s
o f a p p e t i t e ,
a n d w e a k n e s s .
T h e k i d n e y d a m a g e l e a d s t o
c o n d i t i o n s
s u c h a s
a n a e m i a
a n d
h y p e r p a r a t h y r o i d i s m .
DIAGNOSIS AND TREATMENT
A p e r s o n w i t h s u s p e c t e d k i d n e y f a i l u r e
w i l l
i n i t i a l l y
n e e d
b l o o d
a n d
u r i n e
t e s t s . O t h e r t e s t s , s u c h a s
k i d n e y b i o p s y
( e x a m
i n a t i o n
o f a t i s s u e s a m
p l e ) a n d
i n t r a v e n o u s u r o g r a p h y
( t a k i n g X - r a y s o f
t h e u r i n a r y t r a c t ) , m a y b e c a r r i e d o u t
t o i d e n t i f y t h e c a u s e o f t h e k i d n e y f a i l -
u r e i f t h i s i s n o t a l r e a d y o b v i o u s .
I f a c u t e k i d n e y f a i l u r e i s d u e t o a s u d d e n
r e d u c t i o n i n b l o o d f l o w ,
b l o o d v o l u m e
a n d p r e s s u r e c a n b e n o r m a l i z e d b y s a l i n e
i n t r a v e n o u s i n f u s i o n
o r
b l o o d t r a n s f u s i o n
.
I f
t h e r e i s a n o b s t r u c t i o n i n t h e u r i n a r y
t r a c t , s u r g e r y m a y b e n e e d e d . A c u t e k i d -
n e y
d i s e a s e
m a y
b e
t r e a t e d
w i t h
c o r t i c o s t e r o i d d r u g s
.
T r e a t m e n t
m a y
a l s o
i n v o l v e
d i u r e t i c d r u g s
a n d t e m p o r a r y
d i a l y -
s i s
( a r t i f i c i a l p u r i f i c a t i o n o f t h e b l o o d ) .
A h i g h - c a r b o h y d r a t e , l o w - p r o t e i n d i e t
w i t h c o n t r o l l e d f l u i d a n d s a l t i n t a k e i s
i m p o r t a n t i n t h e t r e a t m e n t o f a c u t e a n d
c h r o n i c
k i d n e y
f a i l u r e ,
b e c a u s e
t h i s
r e d u c e s t h e w o r k l o a d o n t h e k i d n e y s .
F o r
e n d - s t a g e
k i d n e y
f a i l u r e ,
l o n g -
t e r m d i a l y s i s o r a
k i d n e y t r a n s p l a n t
i s t h e
o n l y e f f e c t i v e t r e a t m e n t .
k id n e y fu n c tio n te s ts
T e s t s t h a t a r e p e r f o r m e d t o i n v e s t i g a t e
k i d n e y d i s o r d e r s
.
U r i n a l y s i s
i s
a
s i m p l e
t e s t i n w h i c h a u r i n e s a m p l e i s e x a m -
i n e d
u n d e r
a
m i c r o s c o p e
f o r
b l o o d
c e l l s ,
p u s
c e l l s ,
a n d
c a s t s
( c e l l s
a n d
m u c o u s m a t e r i a l t h a t a c c u m u l a t e i n t h e
t u b u l e s o f t h e k i d n e y s a n d p a s s i n t o t h e
u r i n e ) .
U r i n a l y s i s
i s
u s e d
t o
t e s t
f o r
s u b s t a n c e s ,
s u c h a s
p r o t e i n s ,
t h a t l e a k
i n t o
t h e
u r i n e
w h e n
t h e
k i d n e y s
a r e
d a m a g e d . K i d n e y f u n c t i o n c a n b e a s s e s -
s e d b y m e a s u r i n g t h e c o n c e n t r a t i o n i n
t h e b l o o d o f s u b s t a n c e s t h a t t h e k i d n e y s
n o r m a l l y e x c r e t e , s u c h a s
u r e a
a n d
c r e a -
t i n i n e
;
b y c r e a t i n i n e c l e a r a n c e , i n w h i c h
l e v e l s
o f c r e a t i n i n e
i n
t h e
b l o o d
a r e
c o m p a r e d
w i t h
c r e a t i n i n e
e x c r e t e d i n
u r i n e
o v e r
2 4
h o u r s ;
a n d
b y
k i d n e y
i m a g i n g
w i t h r a d i o i s o t o p e s .
k id n e y im a g in g
T e c h n i q u e s f o r v i s u a l i z i n g t h e
k i d n e y s
,
u s u a l l y p e r f o r m e d f o r d i a g n o s i s .
U l t r a s o u n d s c a n n i n g
i s o f t e n t h e f i r s t
i n v e s t i g a t i o n a n d c a n b e u s e d t o i d e n -
t i f y
k i d n e y
e n l a r g e m e n t ,
a
c y s t
o r
t u m o u r ,
a n d t h e s i t e
o f a n y b l o c k a g e .
C o n v e n t i o n a l
X - r a y s
s h o w t h e o u t l i n e o f
t h e
k i d n e y s
a n d
m o s t
k i d n e y
s t o n e s ,
w h i l e
i n t r a v e n o u s u r o g r a p h y
s h o w s
t h e
i n t e r n a l
a n a t o m y
o f
t h e
k i d n e y
a n d
u r e t e r s .
A n g i o g r a p h y
i s
u s e d
t o
i m a g e
b l o o d c i r c u l a t i o n t h r o u g h t h e k i d n e y s .
C T s c a n n i n g
a n d
M R I
p r o v i d e
d e t a i l e d
c r o s s - s e c t i o n a l i m a g e s o f k i d n e y t i s s u e
a n d
t h e
u r i n e - c o l l e c t i n g
s y s t e m ,
a n d
c a n s h o w a b s c e s s e s o r t u m o u r s .
K
449
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