excretory system. excretion rids the body of toxic chemicals, excess water, salts, and carbon...
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Excretory System
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Excretion• Rids the body of toxic chemicals,
excess water, salts, and carbon dioxide
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• Most important substances excreted:–carbon dioxide -
transported to lungs by circulatory system and exhaled
–nitrogen wastes - urea
–water - sweating and urine
Urea
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• Kidneys - regulate amount of water and salt in blood plasma–complex organ
composed of about 1 million microscopic blood filtering units called nephrons
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• Each nephron contains 3 elements:–filtration - the filtration device at the top
of each nephron is the Bowman’s capsule•an arteriole enters and splits into a network of capillaries called a glomerulus
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•The blood pressure inside the glomerulus forces fluid through the capillary walls
•blood cells, proteins, and other large molecules cannot pass through the wall
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•water and small molecules (urea, sodium, and glucose) pass through and enter the hollow interior of the Bowman’s capsule - filtrate
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–Reabsorption•Bowman’s capsule is connected to a long narrow tube called the renal tubule
•the tubule bends back on itself forming a loop – loop of Henle
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•extracts useful molecules (glucose, ions, and some water)
•these molecules reenter bloodstream by passing into capillaries that wrap around the tubule
Kidney cross-section
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–Urine formation (secretion)
•renal tubule empties into a larger tube called a collecting duct
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•collecting duct removes much of the water from the filtrate
•the filtrate that remains after salts, nutrients, and water have been removed is urine
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Urine Removal from the Body
• Urine produced in kidneys passes from kidneys to urinary bladder through the ureters
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• Urinary bladder - hollow, muscular sac that expands as it fills
• Urine leaves bladder and exits body through the urethra
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Kidney Disease• Kidney failure is life threatening• Most common causes:
–infection–long-term diabetes–untreated long-term high blood
pressure–autoimmune kidney disease
Kidney stones
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Kidney Infection
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• Hemodialysis
–tubes are surgically inserted into an artery and a vein
–blood passes from artery to machine to vein
–machine filters blood
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• Kidney transplant
–problem with transplant is rejection
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–histocompatibility antigens - markers on surface of cells that identify them so they are not attacked by the immune system
–the more closely related, the more likely the histocompatibility antigens are common