Organ of osmoregulation and excretion THE KIDNEY Organ of osmoregulation and excretion © 2008 Paul Billiet ODWS

The urinary system Aorta Renal vein Kidney Renal artery Vena cava Ureter Aorta Renal vein Bladder Renal artery Vena cava Urethra © 2008 Paul Billiet ODWS

The Kidney Outer membrane Renal artery Nephrons Renal Vein (2 million) 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 Bowman’s capsule Branch of renal artery Glomerulus Branch of renal vein Branch of renal artery Proximal convoluted tubule Capillary Distil convoluted tubule Collecting duct Loop of Henlé © 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 Southern Illinois School of Medicine Auer Lab Life Sci Div Lawrence Berkley National Lab The filtration membrane is held in place by specialised podocytes © 2008 Paul Billiet ODWS

Blood plasma v Filtrate Component Plasma / mg 100cm-3 Filtrate Urea 0.03 Glucose 0.10 Amino acids 0.05 Salts 0.72 Proteins 8.00 © 2008 Paul Billiet ODWS

The nephron functions Freely permeable to water Impermeable to water Variable permeability to water © 2008 Paul Billiet ODWS

The nephron osmoregulation Active reabsorption Variable permeability to water Impermeable to water Freely permeable to water Na+ Na+ Na+ H2O H2O Passive osmosis Ultrafiltration under pressure 80% of water reabsorbed © 2008 Paul Billiet ODWS

The nephron osmoregulation Variable permeability to water Impermeable to water Freely permeable to water Collecting duct More and more salty Loop of Henlé Na+ H2O H2O © 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 Urea 0.03 2.00 Glucose 0.10 Amino acids 0.05 Salts 0.72 1.50 Proteins © 2008 Paul Billiet ODWS

Reabsorption Microvilli on cuboidal epithelial cells Dr Millet USC Med schooll Kidney tubule with brush border © 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 © 2008 Paul Billiet ODWS