13. How is urine produced in the kidneys? - Renal artery carrying waste material enters the kidney.
- The branches of renal artery take the waste material inside the Bowmans capsule.
- Due to high pressure and diffusion waste material along with lot of water and useful products like glucose amino acids and salt gets filtered from blood to the tubular region of nephron.
- As the filterate moves in the tubular region, water and useful substances are selectively reabsorbed back into the capillaries surrounding the tubular region. These capillaries rejoin to form renal vein. Renal vein carries blood without wastes out of the kidneys.
- The filterate which is urine, is passed to collecting ducts. Collecting ducts passes urine into the ureter which in turn takes it out from kidney into the urinary bladder.
14. With the help of flow chart trace the events
from the moment blood enters kidneys till the formation of
urine. 
15. What is artificial kidney? Some times kidney infection, injury to kidneys or restricted blood flow to kidneys result in kidney damage and its malfunctioning.
In order to clean the metabolic wastes and maintain normal levels of water and minerals ions in body fluids, blood is passed and cleaned by external machine called artificial kidney.
Clean blood is again transferred back into the patient's body. 16. Name the procedure used in the working of an artificial kidney. Dialysis. 17. What is dialysis? Dialysis is the technique of removing excretory wastes and other toxic waste artificially from the blood by passing it through long cellulose tubes coiled in a tank with dialysing solution.
As the blood passes through this artificial kidney the excretory and toxic wastes diffuses out and clean blood is pumped back in to the patient. 18. Draw labelled schematic diagrams of procedure used in artificial kidney. 
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