Organ of osmoregulation and excretion THE KIDNEY Organ of osmoregulation and excretion

The Urinary System Aorta Renal vein Kidney Renal artery Vena cava Ureter Aorta Renal vein Bladder Renal artery Vena cava Urethra

The Kidney Outer membrane Renal artery Nephrons Renal Vein (2 million) Pelvis Cortex Medulla organised in pyramids Ureter Urine

The Blood Supply

The Cortex (view x100) Tubule Malpighian or renal corpuscles

The Malpighian Corpuscle and Bowmans capsule

The Malpighian Corpuscle (view x400) Glomerulus – a ball of capillaries Bowman’s capsule

Medulla (view x400) Tubules Capillaries

Kidney Tubules (view x400)

The nephron In the cortex In the medulla

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

Nephron

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 through the membrane under pressure Proteins do not pass Southern Illinois School of Medicine

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

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

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

The Nephron Functions Freely permeable to water Impermeable to water Variable permeability to water

The Nephron & Osmoregulation Active reabsorption Na+ Na+ Na+ Variable permeability to water Impermeable to water Freely permeable to water H2O H2O Passive osmosis Ultrafiltration under pressure 80% of water reabsorbed

The Nephron & Osmoregulation Collecting duct Variable permeability to water Impermeable to water Freely permeable to water More and more salty Loop of Henlé Na+ H2O H2O

The Nephron & Osmoregulation

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

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

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

Reabsorption Microvilli on cuboidal epithelial cells Dr Millet USC Med schooll Kidney tubule with brush border

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