Скачать или смотреть Forming urine ( influencing factors), Forming dilute urine & Forming concentrated urine

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• The amount of urine produced by the nephron depends on :
• Body fluid volume.
• Body fluid composition.

• Dilute urine is formed when the body is normally hydrated.
• The medullary osmotic gradient determines the osmolarity of the filtrate.
• Filtrate osmolarity increases as it flows down the descending limb of the loop.
• The ascending limb of the loop is highly permeable to solutes, but impermeable to water.
• Filtrate osmolarity decreases as it flows up the ascending limb because the solutes leave and water cannot enter.
• As filtrate enters the distal convoluted tubule its osmolarity is much lower than blood osmolarity.
• Since the distal convoluted tubule and collecting ducts are not very permeable to water but permeable to solutes, filtrate osmolarity continues to decrease.
• Urine exiting the collecting duct has lost most of its solutes and has a very low osmolarity.
• Large volumes of dilute urine are formed.

• When the body is dehydrated, or large amounts of fluids are lost, the nephron produces concentrated urine.
▪ Filtrate production occurs much as it does when the body is not dehydrated.
▪ The high blood osmolarity that occurs during dehydration triggers the release of ADH.
• ADH promotes the production of water pores in the cells of the collecting duct in the medulla.
• As more water is reabsorbed from the collecting ducts, the filtrate osmolarity becomes higher.
• The filtrate becomes more and more concentrated, conserving water.
• The water eventually moves, via osmosis, into the blood, increasing blood volume and decreasing blood osmolarity.