THE KIDNEY
Organ of osmoregulation and
excretion
© 2008 Paul Billiet ODWS
The urinary
system
Aorta
Renal vein
Kidney
Renal artery
Vena cava
Ureter
Bladder
Urethra
© 2008 Paul Billiet ODWS
The Kidney
Outer membrane
Renal
artery
Nephrons
(2 million)
Renal
Vein
Pelvis
Cortex
Medulla organised
in pyramids
Ureter
Urine
© 2008 Paul Billiet ODWS
The blood supply
© 2008 Paul Billiet ODWS
The cortex (view x100)
Tubule
Malpighian or renal corpuscles
© 2008 Paul Billiet ODWS
The Malpighian corpuscle
(view x400)
Glomerulus
– a ball of
capillaries
Bowman’s capsule
© 2008 Paul Billiet ODWS
Medulla (view x400)
Tubules
Capillaries
© 2008 Paul Billiet ODWS
The nephron
In the cortex
In the medulla
© 2008 Paul Billiet ODWS
The nephron
Branch of renal
artery
Branch of renal
vein
Distil convoluted
tubule
Bowman’s capsule
Glomerulus
Proximal
convoluted tubule
Capillary
Collecting duct
Loop of Henlé
© 2008 Paul Billiet ODWS
Filtration in the glomerulus
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Blood enters the glomerulus
from a branch of the renal
artery
This blood is under high
pressure
The capillary walls are one
cell thick
They are pierced with
openings (fenestrations)
The plasma filters though
the membrane under
pressure
Proteins do not pass
© 2008 Paul Billiet ODWS
Southern Illinois School of Medicine
Filtration in the glomerulus
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A membrane surrounds
each capillary of the
glomerulus
The blood plasma is
filtered at about 150 litres
per day
Southern Illinois School of Medicine
© 2008 Paul Billiet ODWS
Filtration in the glomerulus
Southern Illinois School of Medicine
The filtration membrane is
held in place by specialised
podocytes
© 2008 Paul Billiet ODWS
Auer Lab Life Sci Div Lawrence Berkley National Lab
Blood plasma v Filtrate
Component
Plasma
/ mg 100cm-3
Filtrate
/ mg 100cm-3
Urea
0.03
0.03
Glucose
0.10
0.10
Amino acids
0.05
0.05
Salts
0.72
0.72
Proteins
8.00
0
© 2008 Paul Billiet ODWS
The nephron functions
Freely permeable Impermeable Variable permeability
to water
to water
to water
© 2008 Paul Billiet ODWS
The nephron osmoregulation
Active reabsorption
Na+ Na+ Na+
H2O H2O
Passive
osmosis
Ultrafiltration
under pressure
80% of water
reabsorbed
Freely permeable Impermeable Variable permeability
to water
to water
to water
© 2008 Paul Billiet ODWS
The nephron osmoregulation
H2O
H2O
Na+
Na+
Na+
H2O
H2O
H2O
H2O
H2O
H2O
Freely permeable Impermeable Variable permeability
to water
to water
to water
© 2008 Paul Billiet ODWS
More and more salty
Collecting duct
Loop
of
Henlé
The nephron osmoregulation
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The blood concentration is monitored by
osmoreceptors in the hypothalamus
If the concentration rises the hypothalamus
releases ADH
ADH makes the collecting duct walls more
permeable
More water is reabsorbed from the filtrate as
the ducts pass through the salty tissues of
the medulla
© 2008 Paul Billiet ODWS
The nephron osmoregulation
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The urine released into the pelvis is more or
less concentrated depending upon the blood
concentration
Excessive sweating and eating salty food will
produce concentrated urine
Drinking and cold weather will produce dilute
urine
© 2008 Paul Billiet ODWS
Kidney reabsorption
Component
Filtrate
/ mg 100cm-3
Urine
/ mg 100cm-3
Urea
0.03
2.00
Glucose
0.10
0
Amino acids
0.05
0
Salts
0.72
1.50
0
0
Proteins
© 2008 Paul Billiet ODWS
Reabsorption
Microvilli on cuboidal epithelial cells
Kidney tubule with brush border
Dr Millet USC Med schooll
© 2008 Paul Billiet ODWS
The proximal tubules
reabsorb:
80% of water
 All of the glucose
 All of the amino acids
 Blood pH is regulated
 Blood salt levels are regulated
 Urea is left behind and even secreted into the
tubules
Reabsorbed molecules pass into the surrounding
capillaries
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© 2008 Paul Billiet ODWS