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Learn how the kidneys filter blood, process metabolic waste, and produce urine to eliminate toxins. Explore the nephrons and intricate processes involved in urine formation. Discover the importance of reabsorption and secretion in maintaining fluid balance.
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3.12 The Excretory System Pages 210-214
Kidneys • The kidney is the size of a fist and a mass of approximately 500 grams.
Metabolic Waste • Waste is produced from the break-down of proteins.
Deamination • We eat protein. • We use protein for building and repair. • The liver breaks down extra protein. • The amino group, NH2 , is converted to ammonia, NH3 ,
Toxic • The amino group, NH2 , is converted to ammonia, NH3 • Ammonia is toxic! 0.005 mg can kill you!
Solution… • Combining ammonia with carbon dioxide makes urea, [NH2]2CO • Urea is less toxic than ammonia • The blood carries urea to the kidneys where it is excreted in the urine
Kidneys • Filter blood
Renal arteries • Bring blood to the kidney.
Renal Veins • Return “cleaned” blood to the circulatory system.
Ureters • Carry urine from the kidneys to the Bladder.
Bladder control • A sphincter at the base controls the bladder • 200 mL …signal sent “Go to the bathroom” • 400 mL …urgent signal sent “ Go to the bathroom right now!” • 600 mL …too late
Ureter • The tube that carries urine from the bladder to the exterior of the body.
Urine formation • Step #1 filtration • Step #2 reabsorption • Step #3 secretion
Nephrons • One million per kidney
Bowman’s capsule • The cup-like structure that surrounds the glomerulus.
The glomerulus • Cluster of capillaries • The area of fluid filtration
Proximal tubule • a hollow, winding large diameter tube • for the reabsorption of glucose, sodium, amino acids • these are pumped back into the capillaries • urea stays in the tube
Descending loop of Henle • Straight part of the loop moving away from the proximal tubule • Water flows out by osmosis
Ascending Loop of Henle • Straight part of loop heading to distal tubule • Sodium pumped out of tube
Distal tubule • A hollow winding large diameter tube. • Reabsorption of water if needed.
Collecting Duct • System of urine collecting ducts that widen as they near the renal pelvis • Wastes are transferred from the capillary network to the duct. • Water moves by osmosis from the duct to the surrounding blood.
#1 Filtration Moves from glomerulus to Bowman’s capsule: • Water • Salt • Glucose • urea
#1 Filtration Does not move from glomerulus to Bowman’s capsule: • Plasma proteins • Blood cells • Large platelets
volume • 600 mL blood through each kidney per minute
Reabsorption • 119 of every 120 mL of fluid is returned to the blood
Urine • 95% water • 5% salts, urea etc.