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Excretory System
Excretion – removal of metabolic waste
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Urinary system
• made-up of the kidneys, ureters, bladder, and urethra
• kidneys filter waste from blood; collected as urine
• flows through ureters to the bladder
• stored then leaves through urethra
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Kidney Structure
• 3 regions;
• Renal medulla - inner
• Renal cortex – outer part (contains nephrons)
• Renal pelvis - funnel shaped structure in the center of the kidney.
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• 2 blood vessels enter and leave each kidney– renal artery enters – renal vein exists
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Functional Unit of the Kidneys• nephrons
– approx 1 million per kid
• 3 functions: – filtration of water and solutes from the blood – reabsorption of water and molecules back into
the blood – secretion of waste products from surrounding
capillaries
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Filtration• Blood enters a nephron into the glomerulus
• The glomerulus is encased by the Bowman’s capsule– fluid from the blood is filtered– the filtrate contains water, urea, glucose, salts, amino
acids, and vitamins
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• urea - - nitrogenous product made by the liver
• brought to liver as ammonia , converted to less harmful substance (urea) and enters the blood stream
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Reabsorption• Material removed from blood at Bowman’s
cap makes it way back into the blood
• happens along nephron’s tubular parts
Secretion• waste and toxic material secreted from
blood
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• purified blood returned to circulatory sys through renal vein
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Nephron
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The Kidneys ensure that the composition of our Blood remains Constant
• Concentration of water in blood– Drink too much liquid, and the Kidneys will
decrease the rate of reabsorption, excess water is excreted.
• Level of salt in blood– Eat Salty Foods and the Kidneys will respond
by returning less salt to the Blood by reabsorption. Excess is excreted
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• water reabsorption is controlled by the antidiuretic hormone (ADH)
• ADH is released from the pituitary gland in the brain
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Kidney Stones
• excess wastes crystallize