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How the kidney work in excretion explanation, help

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sure.. ok first the kidney is made up tiny tubules called nephrons.. this is where filtration takes place. the kidney is made up of 3 layers, the cortex, medulla and the pelvis.. and connected to the pelvis is the ureter used to take urine to the bladder where its stored before getting removed out through the urethra.
PROCESS OF FILTRATION:
it occurs in 4 steps
1. Ultra Filtration: this is the forcing out of glucose, water, salts, urea and amino acids through the walls of the glomerelus and into the renal capsule.. the pathway is coiled and the blood vessel coming into wide but leaving is thin and narrow thus a very high pressure builds up forcing them out. however there are also tiny spaces thus only small molecules can pass through so amino acids and RBCs arent able to pass
2. Selective Re absorption: this occurs at the loop of Henley in which substances which are required by the body are absorbed back into the blood (by diffusion and by active transport) this is mainly glucose and water
3. Excretion: excreting harmful and toxic material into the blood to mix with urea to form urine. it occurs at the distal convoluted tubule and mainly consists of uretic acid, ammonia and penicillin
4. re absorption of water: this is done at the collecting duct, the kidney is actually very efficient at reabsorbing water almost 99 percent of the water is reabsorbed
 
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Thank u so much, i had a problem in understanding it for a very long time and i can't beleive i finally understood it, thank u very much :D
 
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