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Excretory system – Urinary system Water and Waste Water Balance • 3 Ways we gain water: • Drinking • Food • Chemical Reactions Water Balance 4 Ways we lose water: Sweat Breath Urine Faeces Maintenance of water balance • To maintain water balance, water gain must be equal to water loss. • About 70% human body made up of water • Kidneys regulate the water content of body Water balance Water Gain • 2150 ml in drink & food • 250 ml from chemical reactions • 2500 ml = total gain Water loss • 500 ml in sweat • 400ml in breath • 1500 ml in urine • 100ml in faeces • 2500 ml = total loss Maintenance of water balance If large volume water consumed, kidneys produce large volume of urine If small volume water consumed, kidneys produce small volume of urine Role of ADH Anti-diuretic hormone The kidneys are controlled by ADH ADH is released by pituitary gland and controls the volume of water reabsorbed & returned to bloodstream by the kidneys The kidneys Blood is brought to the kidney in the renal artery. The kidneys filter the blood and then reabsorb useful materials such as glucose. After it has been purified the blood returns to the circulation through the renal vein. Urine is taken from the kidneys to the bladder by the ureters. The bladder stores the urine until it is convenient to expel it from the body. The main waste product removed in the urine is urea. Urea is a waste product produced in the liver when surplus amino acids are broken down to be used for energy. It is released into the bloodstream until it is filtered out and removed by the kidney. Waste Disposal Many harmful wastes such as urea are produced in the body, following chemical reactions Urea is a poisonous nitrogenous waste made in liver by breakdown of excess amino acids Urea passes from liver to blood & transported to kidney where it is removed during filtration Urea dissolved in excess water forms urine and passes to the bladder The Kidney Filtration & Absorption • The renal artery containing unpurified blood enters a kidney & divides into many tiny branches • The blood in each is filtered by a special filtering unit (nephron) • Useful substances are reabsorbed in blood vessels which unite to leave kidney as renal vein (contains purified blood) Nephron • Each filtering unit in a kidney • Consists of cup-shaped Bowman’s capsule leading into long tubule • The renal artery supplying each kidney with blood divides into about a million tiny branches, each of which leads to a glomerulus • The glomerulus is a tiny knot of blood capillaries surrounding a Bowman’s capsule NEPHRON DIAGRAM From renal artery Glomerulus Bowman’s capsule •Water •Glucose •Urea all filtered out. Collecting duct GLUCOSE reabsorbed. WATER reabsorbed. Urea + excess water to renal vein To the URETER The Nephron What is urine? • Excretion from the body • Mainly consists of – UREA – Excess salt – Water • Sterile Urine production • Plasma fluid filters out through pores in the capillary walls & collects in Bowman’s capsule • This glomerular filtrate contains glucose, salts, urea & water • As it passes though kidney tubule, useful substances are reabsorbed into capillaries surrounding tubule • Further water is reabsorbed from liquid flowing down collecting duct Urine production Is so effective 99% water originally present in glomerular filtrate is reabsorbed Final urine contains the urine originally present in the filtrate & excess salts Problems • Too high salt and minerals in diet – Solids precipitating out – Kidney stones • Physical assault on kidneys – damage to kidney tissue resulting in blood in urine • Too much water – Renal failure as kidneys cannot cope with workload