The urinary system
Kidney
Ureter
Aorta
Renal vein
Bladder
Renal artery
Vena cava
Urethra
© 2008 Paul Billiet ODWS
The Kidney
Pelvis
Ureter Medulla organised in pyramids
Cortex
Outer membrane
Renal Vein
Renal artery
Urine
Nephrons(2 million)
© 2008 Paul Billiet ODWS
The Malpighian corpuscle (view x400)
Glomerulus – a ball of capillaries
Bowman’s capsule© 2008 Paul Billiet ODWS
The nephronBowman’s capsule
Glomerulus
Proximal convoluted tubule
Capillary
Loop of Henlé
Collecting duct
Distil convoluted tubule
Branch of renal vein
Branch of renal artery
© 2008 Paul Billiet ODWS
Filtration in the glomerulus 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
Southern Illinois School of Medicine
© 2008 Paul Billiet ODWS
Filtration in the glomerulus
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
The filtration membrane is held in place by specialised podocytes
Auer Lab Life Sci Div Lawrence Berkley National Lab
Southern Illinois School of Medicine
© 2008 Paul Billiet ODWS
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
Variable permeability to water
Impermeable to water
Freely permeable to water
© 2008 Paul Billiet ODWS
The nephron osmoregulation
Variable permeability to water
Impermeable to water
Freely permeable to water
Na+ Na+ Na+
Active reabsorption
H2O H2O
Passive osmosis
80% of water reabsorbed
Ultrafiltration under pressure
© 2008 Paul Billiet ODWS
Variable permeability to water
Impermeable to water
Freely permeable to water
The nephron osmoregulationM
ore an
d m
ore salty
H2O
H2O
H2O
H2O
H2O
H2O
Co
llecting
d
uct
Loop of
Henlé
H2O
H2O
Na+
Na+
Na+
© 2008 Paul Billiet ODWS
The nephron osmoregulation
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
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
Proteins 0 0
© 2008 Paul Billiet ODWS
Reabsorption
Microvilli on cuboidal epithelial cells
Kidney tubule with brush border
Dr Millet USC Med schooll
© 2008 Paul Billiet ODWS
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